Tesis: "Unsteady flow on film cooling"

1

Blake, Sarah Anne. "Turbine blade platform film cooling with simulated stator-rotor purge flow with varied seal width and upstream wake with vortex". [College Station, Tex. : Texas A&M University, 2007. http://hdl.handle.net/1969.1/ETD-TAMU-1340.

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2

Friedrichs, Stefan. "Endwall film-cooling in axial flow turbines". Thesis, University of Cambridge, 1997. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.627225.

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3

Golsen, Matthew J. "Investigation on interactions of unsteady wakes and film cooling on an annular endwall". Honors in the Major Thesis, University of Central Florida, 2011. http://digital.library.ucf.edu/cdm/ref/collection/ETH/id/386.

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In recent decades, greater interest in the effect of rotational wakes on gas turbine film cooling applications has produced increasing numbers of studies on these unsteady phenomena. Wakes are primarily shed from upstream components such as transition duct walls, stator vanes, and rotors. Studies have shown that in areas of unsteady flow, the best performing parameters in conventional steady investigations may not be the best for unsteady applications. One common method of modeling the unsteady wake interaction in subsonic flows is the use of spoke wheel type wake generators using cylindrical rods to produce the velocity detriment and local increase in turbulence intensity. Though the impact of wakes have been studied for decades on airfoil losses and boundary layer transition, only recently has the film cooling and wake interaction been investigated. The existing work is primarily on leading edge models and airfoil cascades. The primary parameter characterizing the unsteady wakes is the dimensionless or reduced frequency known as the Strouhal number. The film cooling jet itself has dominant frequencies resulting from the shear and the jet trailing wake shedding, depending on the injectant flow rate. There exist great deficiencies in the fundamental understanding of the interaction of these two frequencies. Heat transfer considerations are also relatively recent being studied only since the early 1990's. Heat transfer coefficients and film cooling effectiveness have been reported for leading edge and linear airfoil cascades. In the case of the linear cascade, no data can be taken near the endwall region due to the varying tangential velocity of wake generating rod. The current work expands on this initiative incorporating a sector annular duct as the test setting for the rotating wakes focusing on this endwall region.; Studies in to the effect of the rods in this alternate orientation include film cooling effectiveness using temperature sensitive paint, impact of wake rod to film cooling hole diameter ratio, and time accurate numerical predictions and comparisons with experimental work. Data are shown for a range of momentum flux ratios and Strouhal numbers. The result of this work sets the stage for the complete understanding of the unsteady wake and inclined jet interaction.
B.S.M.E.
Bachelors
Engineering and Computer Science
Mechanical Engineering

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4

Popp, Oliver. "Steady and Unsteady Heat Transfer in a Film Cooled Transonic Turbine Cascade". Diss., Virginia Tech, 1999. http://hdl.handle.net/10919/28513.

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The unsteady interaction of shock waves emerging from the trailing edge of modern turbine nozzle guide vanes and impinging on downstream rotor blades is modeled in a linear cascade. The Reynolds number based on blade chord and exit conditions (5*10^6) and the exit Mach number (1.2) are representative of modern engine operating conditions. The relative motion of shocks and blades is simulated by sending a shock wave along the leading edges of the linear cascade instead of moving the blades through an array of stationary shock waves. The blade geometry is a generic version of a modern high turning rotor blade with transonic exit conditions. The blade is equipped with a showerhead film cooling scheme. Heat flux, surface pressure and surface temperature are measured at six locations on the suction side of the central blade. Pressure measurements are taken with Kulite XCQ-062-50a high frequency pressure transducers. Heat flux data is obtained with Vatell HFM-7/L high speed heat flux sensors. High speed heat flux and pressure data are recorded during the time of the shock impact with and without film cooling. The data is analyzed in detail to find the relative magnitudes of the shock effect on the heat transfer coefficient and the recovery temperature or adiabatic wall temperature (in the presence of film cooling). It is shown that the variations of the heat transfer coefficient and the film effectiveness are less significant than the variations of recovery temperature. The effect of the shock is found to be similar in the cases with and without film cooling. In both cases the variation of recovery temperature induced by the shock is shown to be the main contribution to the overall unsteady heat flux. The unsteady heat flux is compared to results from different prediction models published in the literature. The best agreement of data and prediction is found for a model that assumes a constant heat transfer coefficient and a temperature difference calculated from the unsteady surface pressure assuming an isentropic compression.
Ph. D.

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5

Yang, Huitao. "Investigations of flow and film cooling on turbine blade edge regions". Texas A&M University, 2006. http://hdl.handle.net/1969.1/4338.

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The inlet temperature of modern gas turbine engines has been increased to achieve higher thermal efficiency and increased output. The blade edge regions, including the blade tip, the leading edge, and the platform, are exposed to the most extreme heat loads, and therefore, must be adequately cooled to maintain safety. For the blade tip, there is tip leakage flow due to the pressure gradient across the tip. This leakage flow not only reduces the blade aerodynamic performance, but also yields a high heat load due to the thin boundary layer and high speed. Various tip configurations, such as plane tip, double side squealer tip, and single suction side squealer tip, have been studied to find which one is the best configuration to reduce the tip leakage flow and the heat load. In addition to the flow and heat transfer on the blade tip, film cooling with various arrangements, including camber line, upstream, and two row configurations, have been studied. Besides these cases of low inlet/outlet pressure ratio, low temperature, non-rotating, the high inlet/outlet pressure ratio, high temperature, and rotating cases have been investigated, since they are closer to real turbine working conditions. The leading edge of the rotor blade experiences high heat transfer because of the stagnation flow. Film cooling on the rotor leading edge in a 1-1/2 turbine stage has been numerically studied for the design and off-design conditions. Simulations find that the increasing rotating speed shifts the stagnation line from the pressure side, to the leading edge and the suction side, while film cooling protection moves in the reverse direction with decreasing cooling effectiveness. Film cooling brings a high unsteady intensity of the heat transfer coefficient, especially on the suction side. The unsteady intensity of film cooling effectiveness is higher than that of the heat transfer coefficient. The film cooling on the rotor platform has gained significant attention due to the usage of low-aspect ratio and low-solidity turbine designs. Film cooling and its heat transfer are strongly influenced by the secondary flow of the end-wall and the stator-rotor interaction. Numerical predictions have been performed for the film cooling on the rotating platform of a whole turbine stage. The design conditions yield a high cooling effectiveness and decrease the cooling effectiveness unsteady intensity, while the high rpm condition dramatically reduces the film cooling effectiveness. High purge flow rates provide a better cooling protection. In addition, the impact of the turbine work process on film cooling effectiveness and heat transfer coefficient has been investigated. The overall cooling effectiveness shows a higher value than the adiabatic effectiveness does.

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6

Hosder, Serhat. "Unsteady Skin-Friction Measurements on a Maneuvering Darpa2 Suboff Model". Thesis, Virginia Tech, 2001. http://hdl.handle.net/10919/33582.

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Steady and unsteady flow over a generic Suboff submarine model is studied. The skin-friction magnitudes are measured by using hot-film sensors each connected to a constant temperature anemometer. The local minima in the skin-friction magnitudes are used to obtain the separation locations. Steady static pressure measurements on the model surface are performed at 10Â° and 20Â° angles of attack. Steady and unsteady results are presented for two model configurations: barebody and sail-on-side case. The dynamic plunge-pitch-roll model mount (DyPPiR) is used to simulate the pitchup maneuvers. The pitchup maneuver is a linear ramp from 1Â° to 27Â° in 0.33 seconds. All the tests are conducted at ReL=5,500,000 with a nominal wind tunnel speed of 42.7Â±1 m/s. Steady results show that the flow structure on the leeward side of the barebody can be characterized by the crossflow separation. In the sail-on-side case, the separation pattern of the non-sail region follow the barebody separation trend closely. The flow on the sail side is strongly affected by the presence of the sail and the separation pattern is different from the crossflow separation. The flow in the vicinity of the sail-body junction is dominated by the horseshoe type separation. Unsteady results of the barebody and the non-sail region of the sail-on-side case show significant time lags between unsteady and steady crossflow separation locations. These effects produce the difference in separation topology between the unsteady and steady flowfields. A first-order time lag model approximates the unsteady separation locations reasonably well and time lags are obtained by fitting the model equation with the experimental data. The unsteady separation pattern of the sail side does not follow the quasi-steady data with a time lag and the unsteady separation structure is different from the unsteady crossflow separation topology observed for the barebody and the non-sail region of the sail-on-side case.
Master of Science

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7

Al, Shadidi Kamilla. "Oil Cooling of Electric Motor using CFD". Thesis, KTH, Tillämpad termodynamik och kylteknik, 2014. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-149673.

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This thesis investigated the heat transfer of internally oil cooled rotors in permanent magnet electric machines which are, among other things, used in hybrid vehicles or zero emission vehicles. The magnets become sensitive and can be demagnetized at high working temperatures, hence the need of cooling. The scope of this work included CFD simulations in STAR-CCM+. Three different 3D multiphase models simulating the oil propagation in the rotor were performed. A Lagrangian multiphase model combined with a fluid film model was the most suitable model for simulating the spray of the oil and the film thickness along the inner rotor wall. It was noticed that periodic boundaries caused problems for the fluid film model, therefore a complete geometry was preferred over a truncated model. The 3D solutions provided thicker film thicknesses than the analytical solutions from the fluid film thickness theory. The maximum analytical thickness was of the same order of magnitude as the surface average film thickness provided by the multiphase models. This thickness was assumed to be constant when used as the base for the fluid region in the 2D one-phase models.The study showed that aluminum was the most suitable rotor material due to its high conductive capacity, which provided a more even distribution of the temperature in the solid and hence resulted in lower overall temperatures. The cooling power increased linearly with the volumetric flow rate, however the heat transfer coefficient decreased for the higher flow rates. A volumetric flow rate of 10dl/min was recommended. A 2D model was compared to a preliminary experiment and showed that these were not correlated. The conclusion was that more experiments and simulations are needed in order to confirm the validity of the 2D model.

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8

Veley, Emma Michelle. "Measurement of Unsteady Characteristics of Endwall Vortices Using Surface-Mounted Hot-Film Sensors". Wright State University / OhioLINK, 2018. http://rave.ohiolink.edu/etdc/view?acc_num=wright1534450563500249.

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9

Scrittore, Joseph. "Experimental Study of the Effect of Dilution Jets on Film Cooling Flow in a Gas Turbine Combustor". Diss., Virginia Tech, 2008. http://hdl.handle.net/10919/28171.

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Cooling combustor chambers for gas turbine engines is challenging because of the complex flow fields inherent to this engine component. This complexity, in part, arises from the interaction of high momentum dilution jets required to mix the fuel with effusion film cooling jets that are intended to cool the combustor walls. The dilution and film cooling flow have different performance criteria, often resulting in conflicting flow mechanisms. The purpose of this study is to evaluate the influence that the dilution jets have on the film cooling effectiveness and how the flow and thermal patterns in the cooling layer are affected by both the dilution flow and the closely spaced film cooling holes. This study also intends to characterize the development of the flow field created by effusion cooling injection without dilution injection. This work is unique because it allows insight into how the full-coverage discrete film cooling layer is interrupted by high momentum dilution jets and how the surface cooling is affected. The film cooling flow was disrupted along the combustor walls in the vicinity of the high momentum dilution jets and the surface cooling effectiveness was reduced with increased dilution jet momentum. This was due to the secondary flows that were intensified by the increased jet momentum. High turbulence levels were generated at the dilution jet shear layer resulting in efficient mixing. The film cooling flow field was affected by the freestream turbulence and complex flow fields created by the combined dilution and effusion cooling flows both in the near dilution jet region as well as downstream of the jets. Effusion cooling holes inclined at 20Ë created lower coolant layer turbulence levels and higher surface cooling effectiveness than 30Ë cooling holes. Results showed an insensitivity of the coolant penetration height to the diameter and angle of the cooling hole in the region downstream of the dilution mixing jets. When high momentum dilution jets were injected into crossflow, a localized region in the flow of high vorticity and high streamwise velocity was created. When film cooling air was injected the inlet flow field and the dilution jet wake were fundamentally changed and the vortex diminished significantly. The temperature field downstream of the dilution jet showed evidence of a hot region which was moderated appreciably by film cooling flow. Differences in the temperature fields were nominal compared to the large mass flow increase of the coolant. A study of streamwise oriented effusion film cooling flow without dilution injection revealed unique and scaleable velocity profiles created by the closely spaced effusion holes. The effusion cooling considered in these tests resulted in streamwise velocity and turbulence level profiles that scaled well with blowing ratio which is a finding that allows the profile shape and magnitude to be readily determined at these test conditions. Results from a study of compound angle effusion cooling injection showed significant differences between the flow field created with and without crossflow. It was found from the angle of the flow field velocity vectors that the cooling film layer grew nearly linearly in the streamwise direction. The absence of crossflow resulted in higher turbulence levels because there was a larger shear stress due to a larger velocity difference between the coolant and crossflow. The penetration height of the coolant was relatively independent of the film cooling momentum flux ratio for both streamwise oriented and compound angle cooling jets.
Ph. D.

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10

Araújo, Gomes Reinaldo [Verfasser]. "On Aerothermal Effects of Film Cooling on Turbine Blades with Flow Separation / Reinaldo Araújo Gomes". München : Verlag Dr. Hut, 2010. http://d-nb.info/100833121X/34.

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11

Tang, Brian M. T. "Unshrouded turbine blade tip heat transfer and film cooling". Thesis, University of Oxford, 2011. http://ora.ox.ac.uk/objects/uuid:f8479e89-9cd1-4aa7-b5c8-8068ad80de54.

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This thesis presents a joint computational and experimental investigation into the heat transfer to unshrouded turbine blade tips suitable for use in high bypass ratio, large civil aviation turbofan engines. Both the heat transfer to the blade tip and the over-tip leakage flow over the blade tip are characterised, as each has a profound influence on overall engine efficiency. The study is divided into two sections; in the first, computational simulations of a very large scale, low speed linear cascade with a flat blade tip were conducted. These simulations were validated against experimental data collected by Palafox (2006). A thorough assessment of turbulence models and minimum meshing requirements was performed. The standard k-ω and standard k-ϵ turbulence models significantly overpredicted the turbulence levels within the tip gap. The other models were very similar in performance; the SST k-ω and realisable k-ϵ models were found to be the most suitable for the flow environment. The second section documents the development and testing of a novel hybrid blade tip design, the squealet tip, which seeks to combine the known benefits of winglet and double squealer tips. The development of the external geometry was performed primarily through engine-representative CFD simulations at a range of tip gaps from 0.45% to 1.34% blade chord. The squealet tip was found to have a similar aerodynamic sensitivity to tip clearance as a baseline double squealer tip, with a tip gap efficiency exchange rate of 2.03, although this was 18% greater than the alternative winglet tip. The squealet tip displayed higher predicted stage efficiency than the winglet tip over the majority of the range of tip clearances investigated, however. The overall heat load was reduced by 14% compared with the winglet tip but increased by 28% over the double squealer tip, primarily due to the change in wetted surface area. The predicted local heat transfer coefficients were similar across all geometries. A realistic internal cooling plenum and an array of blade tip cooling holes were subsequently added to the squealet tip geometry and the cooling configuration refined by the selective sealing of cooling holes. Film cooling performance was largely assessed by the predicted adiabatic wall temperature distributions. A viable cooling scheme which reduced the cooling air requirement by 38% was achieved, compared to the initial case which had all cooling holes open. This was associated with just a 7% increase in blade tip heat flux and no penalty in peak temperature on the blade tip. Film cooling air ejected from holes on the blade suction side was swept away from the blade tip region, making the squealet rim at the crown of the blade particularly challenging to cool. It was demonstrated that this region could be cooled effectively by ballistic cooling from holes located on the blade tip cavity floor, although this was expensive in terms of the mass flow rate of cooling air required. The computational results were reinforced with experimental data collected in a transonic linear cascade. Downstream aerodynamic loss measurements were taken for a linearised version of the squealet tip design without cooling at nominal tip gaps of 0.45%, 0.89% and 1.34% blade chord, which was compared to similar data taken by O’Dowd (2010) for flat and winglet tips. The squealet was seen to have a similar aerodynamic loss to the flat tip and a reduced loss compared with the winglet tip. Full surface heat transfer measurements were taken for the uncooled squealet tip, at tip gaps of 0.89% and 1.34% blade chord, and for two configurations of the cooled squealet tip, at a tip clearance of 0.89% blade chord. The qualitative similarity between the measured heat transfer distributions and the those predicted by the engine-representative CFD simulations was good. A CFD simulation of the uncooled linear cascade environment at the 1.34% blade chord tip clearance was performed using a single blade with translationally periodic boundary conditions. The predicted size of the over-tip leakage vortex was smaller than had been measured, resulting in a large underprediction in the magnitude of the downstream area-averaged aerodynamic loss. The magnitudes of the predicted blade tip Nusselt number distribution were similar to those produced by the engine-representative CFD simulations and lower than that measured experimentally. Differences in the shape of the Nusselt number distribution were observed in the vicinity of regions of separated and reattaching flow, but other salient features were replicated in the computational data. The squealet tip has been shown to be a promising, viable unshrouded blade tip design with an aerodynamic performance similar to the double squealer tip but is more amenable to film cooling. It is significantly lighter than a winglet tip and incurs a reduced thermal load. The squealet tip design can now be developed into a blade tip geometry for use in real engines to provide an alternative to shrouded turbine blades and current unshrouded blade tip designs. A commercial CFD solver, Fluent 6.3, was shown to capture blade tip heat transfer and over-tip leakage flow sufficiently well to be a useful design guide. However, the sensitivity of the flow structure (and hence, heat transfer) in the forward part of the blade tip cavity suggests that physical testing cannot be eliminated from the design process entirely.

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12

Kartuzova, Olga V. "A computational study for the utilization of jet pulsations in gas turbine film cooling and flow control". Cleveland, Ohio : Cleveland State University, 2010. http://rave.ohiolink.edu/etdc/view?acc_num=csu1277733325.

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Thesis (Ph.D.)--Cleveland State University, 2010.
Abstract. Title from PDF t.p. (viewed on July 6, 2010). Includes bibliographical references (p. 154-162). Available online via the OhioLINK ETD Center and also available in print.

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13

Leung, Pak Wing. "Aerodynamic Loss Co-Relations and Flow- Field Investigations of a Transonic Film- Cooled Nozzle Guide Vane". Thesis, KTH, Kraft- och värmeteknologi, 2015. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-162130.

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Over the last two decades, most developed countries have reached a consensus that greener energy production is necessary for the world, due to the climate changes and limited fossil fuel resources. More efficient turbine is desirable and can be archived by higher turbine-inlet temperature (TIT). However, it is difficult for nozzle guide vane (NGV), which is the first stage after combustion chamber, to withstand a very high temperature. Thus, cooling methods such as film cooling have to be implemented. Film-cooled NGV of an annular sector cascade (ASC) is studied in this thesis, for getting comprehensive calculation of vorticity, and analyzing applicability of existing loss models, namely Hartsel model and Young & Wilcock model. The flow-field calculation methods from previously published studies are reviewed. Literatures focusing on Hartsel model and Young & Wilcock model are studied. Measurement data from previously published studies are analyzed and compared with the loss models. In order to get experience of how measurements take place, participation of a test run experiment is involved. Calculation of flow vector has been evaluated and modified. Actual flow angle is introduced when calculating velocity components. Thus, more exact results are obtained from the new method. Calculation of vorticity has been evaluated and made more comprehensive. Vorticity components as well as magnitude of total streamwise vorticity are calculated and visualized. Vorticity is higher and more extensive for fully cooled case than uncooled case. Highest vorticity is found at regions near the hub, tip and TE. Axial and circumferential vorticities show similar patterns, while the radial vorticity is relatively simpler. Compressibility is introduced as a new method when calculating circumferential and radial vorticities, resulting more extensive and higher vorticities than results from incompressible solutions. Hartsel model and Young & Wilcock model have been evaluated and compared to the ASC to see the applicability of the models. In general, Hartsel model cannot agree with the ASC to a satisfactory level and thus cannot be applied. Coolant velocity is found to be the dominant factor of Hartsel model. Young & Wilcock model may match SS1 and SS2 cases, or even PS and SH4 cases, but cannot match TE case. The applicability of Young & Wilcock model is much dependent on the location of cooling rows.

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14

GALETTI, MARIA REGINA DA SILVA. "HEAT AND MASS TRANSFER COOLING OF A VERTICAL SURFACE BY A LIQUID FILM WITH AIR FLOW". PONTIFÍCIA UNIVERSIDADE CATÓLICA DO RIO DE JANEIRO, 1995. http://www.maxwell.vrac.puc-rio.br/Busca_etds.php?strSecao=resultado&nrSeq=19415@1.

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Uma das características das alternativas consideradas para o desenvolvimento de reatores nucleares com características avançadas de segurança consiste na utilização de resfriamento do vaso de contenção com um fluxo de água vindo de seu topo. Este sistema forma um escoamento de um filme líquido evaporando sobre uma superfície metálica aquecida com ar escoando em contra-corrente. O presente trabalho consiste no desenvolvimento de um modelo analítico e numérico da transferência de calor e massa que ocorre na interface entre o filme líquido e a mistura ar-vapor, neste tipo de escoamento e também em escoamentos co-correntes. Devido à ausência de dados experimentais, o modelo é validado através de comparações com resultados analíticos disponíveis na literatura para situações próximas aos casos de interesse. A influência de diversos parâmetros geométricos e operacionais é analisada e são fornecidos resultados para os números de Nusselt e de Sherwood observados na interface do escoamento das fases.
The design of so called Advanced Nuclear reactors includes many features of passive safety, one of them being a water flow system for cooling the containment vessel. This system generates a counter-current flow pattern with a downward liquid film evaporating over the heated vessel surface and na upward stream of air. This work presents an analytical and numerical model for analysis of heat and mass transfer occuring in the interface formed by water film surfece anda ir-vapor mixture in counter-curent and parallel flows. Due to the lack of experimental data, the model is validated throught comparisons with analytical results found in the flow analysed and the results for Nusselt and Sherwood numbers are presented.

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15

Rozati, Ali. "Large Eddy Simulation of Leading Edge Film Cooling: Flow Physics, Heat Transfer, and Syngas Ash Deposition". Diss., Virginia Tech, 2007. http://hdl.handle.net/10919/30127.

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The work presented in this dissertation is the first numerical investigation conducted to study leading edge film cooling with Large Eddy Simulation (LES). A cylindrical leading edge with a flat after-body represents the leading edge, where coolant is injected with a 30Ë compound angle. Three blowing ratios of 0.4, 0.8, and 1.2 are studied. Free-stream Reynolds number is 100,000 and coolant-to-mainstream density ratio is unity. At blowing ratio of 0.4, the effect of coolant inlet condition is investigated. Results show that the fully-turbulent coolant jet increases mixing with the mainstream in the outer shear layer but does not influence the flow dynamics in the turbulent boundary layer at the surface. As a result, the turbulent jet decreases adiabatic effectiveness but does not have a substantial effect on the heat transfer coefficient. At B.R.=0.4, three types of coherent structures are identified which consist of a primary entrainment vortex at the leeward aft-side of the coolant hole, vortex tubes at the windward side of the coolant hole, and hairpin vortices typical of turbulent boundary layers produced by the turbulent interaction of the coolant and mainstream downstream of injection. At B.R. = 0.8 and 1.2, coherent vortex tubes are no longer discernable, whereas the primary vortex structure gains in strength. In all cases, the bulk of the mixing occurs by entrainment which takes place at the leeward aft-side of the coolant jet. This region is characterized by a low pressure core and the primary entrainment vortex. Turbulent shear interaction between coolant jet and mainstream increases substantially with blowing ratio and contributes to the dilution of the coolant jet. As a result of the increased mixing in the shear layer and primary structure, adiabatic effectiveness decreases and heat transfer coefficient increases with increase in blowing ratio. The dissertation also investigates the deposition and erosion of Syngas ash particles in the film cooled leading edge region. Three ash particle sizes of 1, 5, and 10 microns are investigated at all blowing ratios using Lagrangian dynamics. The 1 micron particles with momentum Stokes number St = 0.03 (based on approach velocity and cylinder diameter), show negligible deposition/erosion. The 10 micron particles, on the other hand with a high momentum Stokes number, St = 3, directly impinge and deposit on the surface, with blowing ratio having a minimal effect. The 5 micron particles with St=0.8, show the largest receptivity to coolant flow and blowing ratio. On a mass basis, 90% of deposited mass is from 10 micron particles, with 5 micron particles contributing the other 10%. Overall there is a slight decrease in deposited mass with increase in blowing ratio. About 0.03% of the total incoming particle energy can potentially be transferred as erosive energy to the surface and coolant hole, with contribution coming from only 5 micron particles at B.R.=0.4 and 0.8, and both 5 and 10 micron particles at B.R.=1.2.
Ph. D.

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16

Stathopoulos, Nicholas. "Influence of upstream turbulence on discrete-hole film cooling of a model blade in confined cross flow". Thesis, McGill University, 1994. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=26422.

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An experimental investigation of the influence of upstream turbulence on discrete-hole film cooling of a model blade in confined cross flow is presented and discussed. A model blade and test section were designed and constructed. A system for constant-temperature hot-wire anemometry was implemented. A microcomputer-based data acquisition, control, and processing system was designed and implemented. The model blade was a blunt body with a semicircular leading edge, a flat after body, and a tapered trailing edge. Local heat transfer coefficients without injection of a secondary fluid were determined using a thin-film technique. In the film cooling studies, two rows of discrete injection holes at $ pm$30$ sp circ$ from the stagnation line were used. The injection tubes were oriented normal to the surface of the model blade and were coplanar with the primary flow velocity vector.
Nominal turbulence intensities of 0.7%, 9.8%, and 14.4% at a location 1.3 diameters upstream of the stagnation line on the semicircular leading edge of the model blade were investigated. The range of Reynolds number, based on the diameter of the semicircular leading edge and upstream velocity, was 23,000 to 75,000. In the discrete-hole film cooling studies, mass flux ratios in the range 0.6 $<$ M $<$ 2.0 were considered. The heat transfer results are presented in terms of the distributions of local Nusselt number and a nondimensional temperature on the surface of the blade. The results of the film cooling studies are presented in terms of the distributions of the effectiveness.

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17

Nguyen, Cuong Quoc. "Interaction between secondary flow & film cooling jets of a realistic annular airfoil cascade (high mach number)". Doctoral diss., University of Central Florida, 2010. http://digital.library.ucf.edu/cdm/ref/collection/ETD/id/4601.

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Film cooling is investigated on a flat plate both numerically and experimentally. Conical shaped film hole are investigated extensively and contribute to the current literature data, which is extremely rare in the open public domain. Both configuration of the cylindrical film holes, with and without a trench, are investigated in detail. Design of experiment technique was performed to find an optimum combination of both geometrical and fluid parameters to achieve the best film cooling performance. From this part of the study, it shows that film cooling performance can be enhanced up to 250% with the trenched film cooling versus non-trenched case provided the same amount of coolant. Since most of the relevant open literature is about film cooling on flat plate endwall cascade with linear extrusion airfoil, the purpose of the second part of this study is to examine the interaction of the secondary flow inside a 3D cascade and the injected film cooling jets. This is employed on the first stage of the aircraft gas turbine engine to protect the curvilinear (annular) endwall platform. The current study investigates the interaction between injected film jets and the secondary flow both experimentally and numerically at high Mach number (M=0.7). Validation shows good agreement between obtained data with the open literature. In general, it can be concluded that with an appropriate film coolant to mainstream blowing ratio, one can not only achieve the best film cooling effectiveness (FCE or eta]) on the downstream endwall but also maintain almost the same aerodynamic loss as in the un-cooled baseline case. Film performance acts nonlinearly with respect to blowing ratios as with film cooling on flat plate, in the other hand, with a right blowing ratio, film cooling performance is not affect much by secondary flow. In turn, film cooling jets do not increase pressure loss at the downstream wake area of the blades.
ID: 029050151; System requirements: World Wide Web browser and PDF reader.; Mode of access: World Wide Web.; Thesis (Ph.D.)--University of Central Florida, 2010.; Includes bibliographical references (p. 146-149).
Ph.D.
Doctorate
Department of Mechanical, Materials and Aerospace Engineering
Engineering and Computer Science
Thermo-Fluid Sciences

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18

Kartuzova, Olga Valeryevna. "A computational study for the utilization of jet pulsations in gas turbine film cooling and flow control". Cleveland State University / OhioLINK, 2010. http://rave.ohiolink.edu/etdc/view?acc_num=csu1277733325.

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19

Sinitsin, David M. "A numerical and experimental study of flow and heat transfer from a flush inclined film cooling slot". Thesis, University of British Columbia, 1988. http://hdl.handle.net/2429/28064.

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Numerical and experimental results are presented for a simple, two dimensional flow from a flush, inclined slot in a flat plate. The geometry and mass flow conditions represent film cooling flows issuing from flush, inclined slots. The numerical velocity field predictions compare favourably with detailed flow measurements. Preliminary calculations of the heat transfer downstream of injection are also presented. Work done subsequent to this thesis indicates that the slot flow rate calibration may have been incorrect by 13 percent during the experiments. No correction for this possibility has been made here but a change, if made, would reduce the measured mass flow rates by 13 percent and would probably improve the agreement between measured and calculated velocity distributions. Experimental observations and measurements indicate that the velocity of the flow exiting the slot is non-uniform in both magnitude and direction. The variation of flow direction in the slot could not be measured in this study. Consequently, several assumed distributions are used to elucidate the effect of flow angle variation on film cooling performance. The flow field is shown to be essentially insensitive to the non-uniformities in magnitude and direction of the slot flow. However, the predictions of wall shear stress and wall heat transfer downstream of injection are significantly affected by the non-uniformities in the slot. Differences of 80 to 100 percent are predicted depending on the flow angle distribution. These effects are shown to be most significant within 40 slot widths of the slot. The results presented here may have important implications in prediction of the performance of various film cooling schemes. Furthermore, they point to a need for detailed flow measurements within and near modern film cooling orifices.
Applied Science, Faculty of
Mechanical Engineering, Department of
Graduate

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20

Davis, Shanon Marie. "Heat-Flux Measurements for a Realistic Cooling Hole Pattern and Different Flow Conditions". The Ohio State University, 2011. http://rave.ohiolink.edu/etdc/view?acc_num=osu1315013452.

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21

White, Jonathan Charles. "HIGH-FRAME-RATE OIL FILM INTERFEROMETRY". DigitalCommons@CalPoly, 2011. https://digitalcommons.calpoly.edu/theses/572.

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High-Frame-Rate Oil Film Interferometry Jonathan Charles White This thesis presents the design and implementation of a high-frame-rate oil film interferometry technique (HOFI) used to directly measure skin friction in time dependent flows. Experiments were performed to determine the ability of a high-speed camera to capture oil film interferometry images. HOFI was found to be able to capture these interferometry images at frequencies up to 105 Hz. Steady laminar and turbulent flows were tested. Transient flows tested consisted of a wind tunnel ramping up in velocity and a laminar boundary layer which was intermittently tripped to turbulence by puffing air out of a pressure tap. Flow speeds ranged from 0 to 108 ft/sec and 10 and 50 cSt Dow Corning 200 dimethylpolysiloxane silicone oil was used. The skin friction was determined from the rate of change of the height of the oil film using lubrication theory. The height of the oil film was determined from the high speed camera interferogram images using a MATLAB script which determined fringe spacing by fitting a four-parameter sine wave to the intensity levels in each image. The MATLAB script was able to determine the height of the oil film for thousands of interferogram images in only a few minutes with sub-pixel error in fringe spacing. The skin friction was calculated using the oil film height history allowing for the direct measurement of skin friction in time dependent flows.

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22

Grabowski, Henry Casmir. "Updating and Automating the Virginia Tech Single-Plate Interferometer". Thesis, Virginia Tech, 1999. http://hdl.handle.net/10919/35247.

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The single-plate interferometer is a powerful flow visualization and aerodynamic measurement tool. It can provide full-field data for the density distribution in a non-intrusive manner, and it can be used for highly unsteady flows. While the device itself represents a large decrease in complexity over other forms of interferometry, the data reduction procedure has traditionally been laborious and difficult. To remove these difficulties and to improve the accuracy of the Virginia Tech interferometer setup, the software has been revamped into a black box design removing the need to handle the code directly. Furthermore, the software has been made to be platform independent by implementing the algorithms using the Java programming language. New hardware has also been added which further simplifies the setup procedure.

The improved setup and the new software is used to study the flow around a film cooled turbine blade in the Virginia Tech cascade wind tunnel. The study of this flowfield is used as a validation for the new algorithms and to illustrate the ease of use of the system. Through this analysis, the density distribution for the entire flowfield is acquired. Furthermore the use of Plexiglas as window material was tried. This proved to work, however the manufacturing processing of these windows proved relatively difficult. Studying the film layer close to the surface proved difficult because of inherent limitations with the single-plate interferometer.
Master of Science

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23

Casey, Timothy. "The aerodynamic losses with the addition of film cooling in a high-speed annular cascade". Honors in the Major Thesis, University of Central Florida, 2010. http://digital.library.ucf.edu/cdm/ref/collection/ETH/id/1375.

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This item is only available in print in the UCF Libraries. If this is your Honors Thesis, you can help us make it available online for use by researchers around the world by following the instructions on the distribution consent form at http://library.ucf.edu/Systems/DigitalInitiatives/DigitalCollections/InternetDistributionConsentAgreementForm.pdf You may also contact the project coordinator, Kerri Bottorff, at kerri.bottorff@ucf.edu for more information.
Bachelors
Engineering and Computer Science
Mechanical Engineering

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24

Van, Hout Daniel Richard. "Heat Transfer and Film Cooling Performance on a Transonic Converging Nozzle Guide Vane Endwall With Purge Jet Cooling and Dual Cavity Slashface Leakage". Thesis, Virginia Tech, 2020. http://hdl.handle.net/10919/100799.

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The following study presents an experimental and computational investigation on the effects of implementing a dual cavity slashface configuration and varying slashface coolant leakage mass flow rate on the thermal performance for a 1st stage nozzle guide vane axisymmetric converging endwall. An upstream doublet staggered cylindrical hole jet cooling scheme provides additional purged coolant with consistent conditions throughout the investigation. The effects are measured in engine representative transonic mainstream and coolant flow conditions where Mexit = 0.85, Reexit = 1.5 × 106, freestream turbulence intensity of 16%, and a coolant density ratio of 1.95. Four combinations of slashface Fwd and Aft cavity mass flow rate are experimentally analyzed by comparing key convective heat transfer parameters. Data is collected and reduced using a combination of IR thermography and a linear regression technique to map endwall heat transfer performance throughout the passage. A flow visualization study is employed using 100 cSt oil-based paint to gather qualitative insights into the endwall flow field. A complimentary CFD study is carried out to gather additional understanding of the endwall flow ingestion and egression behavior as well as comparing performance against a conventional cavity configuration. Experimental comparisons indicate slashface mass flow rate variations have a minor effect on passage film cooling coverage. Instead, coolant coverage across the passage is primarily driven by upstream purge coolant. However, endwall heat transfer coefficient is reduced as much as 20% in mid-passage areas as leakage flow decreases. This suggests that changes in leakage flow maintains a first order correlation in altering passage aerodynamics that, despite relatively consistent film cooling coverage, also leads to significant changes in net heat flux reduction in the passage. Endwall flow behavior proves to be complex along the gap interface showing signs of ingestion, egression, and tangential flow varying spatially throughout the gap. CFD comparisons suggests that a dual cavity configuration varies the gap static pressure distribution closer to the mainstream pressure throughout the passage in high speed applications compared to a single cavity configuration. The resulting decelerating flow creates a more stable endwall flow profile and favorable coolant environment by reducing boundary layer thinning and shear interaction in near gap endwall tangential flow.
Master of Science
Gas turbines are often exposed to high temperatures as they convert hot, energetic gas streams into mechanical motion. As turbines receive higher temperature gases, their efficiency increases and reduces waste. However, these temperatures can get too hot for turbine parts. To survive these high temperatures, turbine components are often assembled with a gap in between to allow the part to expand and contrast when it heats and cools. Relatively cold air is also fed into the gap to help prevent hot gases from entering. This cold air can also feed into other pathways to flow onto the turbine component's surface and act as an insulating layer to the hot gas and protect the component from overheating. The study presented investigates an assembly gap, referred to as a slashface gap, found in the middle of a vane located immediately after gas combustion with cold air leaking through. One unique aspect of this study is that there are two pathways for cold air, or coolant, to leak through when, typically, there is only one. The slashface gap lies on a wall which the vanes are attached to, referred to as the endwall. Multiple small holes on the endwall in between the combustor and vanes jet out coolant to try and protect the endwall from hot gases. These holes, called jump cooling holes, point out towards the vanes and angled more shallowly so that the holes do not face directly up from the endwall. The holes are angled as they are meant to gracefully spray coolant to cover and insulate the endwall instead of mixing with the hot air above. The experiments found that changing how much coolant is leaked through the slashface has little effect on how much coolant from jump cooling holes covered the endwall. However, smaller slashface leaks better protect the endwall from the hot gas by forcing it to move smoother and give off less heat across the endwall rather than a tumbling like manner. The experiment is modeled on a computer simulation to determine the differences of a slashface gap with the typical one coolant pathway and the coolant dual pathway configuration that is tested in the experiments. This simulation discovered that having two coolant pathways significantly reduces how much hot gas and jump cooling coolant enters and leaves the slashface gap. This makes the surrounding airflow along the endwall travel more smoothly and does not give off as much heat as if a single coolant pathway configuration is used instead.

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25

Boehler, Michael David. "Transient Aerothermodynamics of Flow Initialization for a Flat Plate Film Cooling Experiment in a Medium Duration Blowdown Wind Tunnel Facility". The Ohio State University, 2010. http://rave.ohiolink.edu/etdc/view?acc_num=osu1284767673.

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26

Saha, Ranjan. "Aerodynamic Investigation of Leading Edge Contouring and External Cooling on a Transonic Turbine Vane". Doctoral thesis, KTH, Kraft- och värmeteknologi, 2014. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-150458.

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Efficiency improvement in turbomachines is an important aspect in reducing the use of fossil-based fuel and thereby reducing carbon dioxide emissions in order to achieve a sustainable future. Gas turbines are mainly fossil-based turbomachines powering aviation and land-based power plants. In line with the present situation and the vision for the future, gas turbine engines will retain their central importance in coming decades. Though the world has made significant advancements in gas turbine technology development over past few decades, there are yet many design features remaining unexplored or worth further improvement. These features might have a great potential to increase efficiency. The high pressure turbine (HPT) stage is one of the most important elements of the engine where the increased efficiency has a significant influence on the overall efficiency as downstream losses are substantially affected by the prehistory. The overall objective of the thesis is to contribute to the development of gas turbine efficiency improvements in relation to the HPT stage. Hence, this study has been incorporated into a research project that investigates leading edge contouring near endwall by fillet and external cooling on a nozzle guide vane with a common goal to contribute to the development of the HPT stage. In the search for HPT stage efficiency gains, leading edge contouring near the endwall is one of the methods found in the published literature that showed a potential to increase the efficiency by decreasing the amount of secondary losses. However, more attention is necessary regarding the realistic use of the leading edge fillet. On the other hand, external cooling has a significant influence on the HPT stage efficiency and more attention is needed regarding the aerodynamic implication of the external cooling. Therefore, the aerodynamic influence of a leading edge fillet and external cooling, here film cooling at profile and endwall as well as TE cooling, on losses and flow field have been investigated in the present work. The keystone of this research project has been an experimental investigation of a modern nozzle guide vane using a transonic annular sector cascade. Detailed investigations of the annular sector cascade have been presented using a geometric replica of a three dimensional gas turbine nozzle guide vane. Results from this investigation have led to a number of new important findings and also confirmed some conclusions established in previous investigations to enhance the understanding of complex turbine flows and associated losses. The experimental investigations of the leading edge contouring by fillet indicate a unique outcome which is that the leading edge fillet has no significant effect on the flow and secondary losses of the investigated nozzle guide vane. The reason why the leading edge fillet does not affect the losses is due to the use of a three-dimensional vane with an existing typical fillet over the full hub and tip profile. Findings also reveal that the complex secondary flow depends heavily on the incoming boundary layer. The investigation of the external cooling indicates that a coolant discharge leads to an increase of profile losses compared to the uncooled case. Discharges on the profile suction side and through the trailing edge slot are most prone to the increase in profile losses. Results also reveal that individual film cooling rows have a weak mutual effect. A superposition principle of these influences is followed in the midspan region. An important finding is that the discharge through the trailing edge leads to an increase in the exit flow angle in line with an increase of losses and a mixture mass flow. Results also indicate that secondary losses can be reduced by the influence of the coolant discharge. In general, the exit flow angle increases considerably in the secondary flow zone compared to the midspan zone in all cases. Regarding the cooling influence, the distinct change in exit flow angle in the area of secondary flows is not noticeable at any cooling configuration compared to the uncooled case. This interesting zone requires an additional, accurate study. The investigation of a cooled vane, using a tracer gas carbon dioxide (CO2), reveals that the upstream platform film coolant is concentrated along the suction surfaces and does not reach the pressure side of the hub surface, leaving it less protected from the hot gas. This indicates a strong interaction of the secondary flow and cooling showing that the influence of the secondary flow cannot be easily influenced. The overall outcome enhances the understanding of complex turbine flows, loss behaviour of cooled blade, secondary flow and interaction of cooling and secondary flow and provides recommendations to the turbine designers regarding the leading edge contouring and external cooling. Additionally, this study has provided to a number of new significant results and a vast amount of data, especially on profile and secondary losses and exit flow angles, which are believed to be helpful for the gas turbine community and for the validation of analytical and numerical calculations.
Ökad verkningsgrad i turbomaskiner är en viktig del i strävan att minska användningen av fossila bränslen och därmed minska växthuseffekten för att uppnå en hållbar framtid. Gasturbinen är huvudsakligen fossilbränslebaserad, och driver luftfart samt landbaserad kraftproduktion. Enligt rådande läge och framtidsutsikter bibehåller gasturbinen denna centrala roll under kommande decennier. Trots betydande framsteg inom gasturbinteknik under de senaste årtionden finns fortfarande många designaspekter kvar att utforska och vidareutveckla. Dessa designaspekter kan ha stor potential till ökad verkningsgrad. Högtrycksturbinsteget är en av de viktigaste delarna av gasturbinen, där verkningsgraden har betydande inverkan på den totala verkningsgraden eftersom förluster kraftigt påverkas av tidigare förlopp. Huvudsyftet med denna studie är att bidra till verkningsgradsförbättringar i högtrycksturbinsteget. Studien är del i ett forskningsprojekt som undersöker ledskenans framkantskontur vid ändväggarna samt extern kylning, i jakten på dessa förbättringar. Den aerodynamiska inverkan av en förändrad geometri vid ledskenans ändväggar har i tidigare studier visat potential för ökad verkningsgrad genom minskade sekundärförluster. Ytterligare fokus krävs dock, med användning av en rimlig hålkälsradie. Samtidigt har extern kylning i form av filmkylning stor inverkan på verkningsgraden hos högtrycksturbinsteget och forskning behövs med fokus på den aerodynamiska inverkan. Av denna anledning studeras här inverkan både av ändrad hålkälsradie vid ledskenans framkant samt extern kylning i form av filmkylning av skovel, ändvägg och bakkant på aerodynamiska förluster och strömningsfält. Huvudpelaren i detta forskningsprojekt har varit en experimentell undersökning av en geometrisk replika av en modern tredimensionell gasturbinstator i en transonisk annulärkaskad. Detaljerade undersökningar i annulärkaskaden har gett betydande resultat, och bekräftat vissa tidigare studier. Detta har lett till ökad förståelsen för de komplexa flöden och förluster som karakteriserar gasturbiner. De experimentella undersökningarna av förändrad framkantsgeometri leder till den unika slutsatsen att den modifierade hålkälsradien inte har någon betydande inverkan på strömningsfältet eller sekundärförluster av den undersökta ledskenan. Anledningen till att förändringen inte påverkar förlusterna är i detta fall den tredimensionella karaktären hos ledskenan med en redan existerande typisk framkantsgeometri. Undersökningarna visar också att de komplexa sekundärströmningarna är kraftigt beroende av det inkommande gränsskiktet. Undersökning av extern kylning visar att kylflödet leder till en ökad profilförlust. Kylflöde på sugsidan samt bakkanten har störst inverkan på profilförlusten. Resultaten visar också att individuella filmkylningsrader har liten påverkan sinsemellan och kan behandlas genom en superpositionsprincip längs mittsnittet. En viktig slutsats är att kylflöde vid bakkanten leder till ökad utloppsvinkel tillsammans med ökade förluster och massflöde. Resultat tuder på att sekundärströmning kan minskas genom ökad kylning. Generellt ökar utloppsvinkeln markant i den sekundära flödeszonen jämfört med mittsnittet för alla undersökta fall. Den kraftiga förändringen i utloppsvinkel är dock inte märkbar i den sekundära flödeszonen i något av kylfallen jämfört med de okylda referensfallet. Denna zon fordrar ytterligare studier. Spårgasundersökning av ledskenan med koldioxid (CO2) visar att plattformskylning uppströms ledskenan koncentreras till skovelns sugsida, och når inte trycksidan som därmed lämnas mer utsatt för het gas. Detta påvisar den kraftiga interaktionen mellan sekundärströmning och kylflöden, och att inverkan från sekundärströmningen ej enkelt kan påverkas. De generella resultaten från undersökningen ökar förståelsen av komplexa turbinflöden, förlustbeteenden för kylda ledskenor, interaktionen mellan sekundärströmning och kylflöden, och ger rekommendationer för turbinkonstruktörer kring förändrad framkantsgeometri i kombination med extern kylning. Dessutom har studien gett betydande resultat och en stor mängd data, särskilt rörande profil- och sekundärförluster och utloppsvinkel, vilket tros kunna vara till stor hjälp för gasturbinssamfundet vid validering av analytiska och numeriska beräkningar.

QC 20140909

Turbopower, Sector rig

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27

Peterson, Blair A. "A Study of Blockage due to Ingested Airborne Particulate in a Simulated Double-Wall Turbine Internal Cooling Passage". The Ohio State University, 2015. http://rave.ohiolink.edu/etdc/view?acc_num=osu1429738411.

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Johnson, Perry L. "Toward increasing performance and efficiency in gas turbines for power generation and aero-propulsion unsteady simulation of angled discrete-injection coolant in a hot gas path crossflow". Honors in the Major Thesis, University of Central Florida, 2011. http://digital.library.ucf.edu/cdm/ref/collection/ETH/id/444.

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This thesis describes the numerical predictions of turbine film cooling interactions using Large Eddy Simulations. In most engineering industrial applications, the Reynolds-Averaged Navier-Stokes equations, usually paired with two-equation models such as k-Greek lowercase letter epsilon] or k-Greek lowercase letter omega], are utilized as an inexpensive method for modeling complex turbulent flows. By resolving the larger, more influential scale of turbulent eddies, the Large Eddy Simulation has been shown to yield a significant increase in accuracy over traditional two-equation RANS models for many engineering flows. In addition, Large Eddy Simulations provide insight into the unsteady characteristics and coherent vortex structures of turbulent flows. Discrete hole film cooling is a jet-in-cross-flow phenomenon, which is known to produce complex turbulent interactions and vortex structures. For this reason, the present study investigates the influence of these jet-crossflow interactions in a time-resolved unsteady simulation. Because of the broad spectrum of length scales present in moderate and high Reynolds number flows, such as the present topic, the high computational cost of Direct Numerical Simulation was excluded from possibility.
B.S.M.E.
Bachelors
Engineering and Computer Science
Mechanical Engineering

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29

Sibold, Ridge Alexander. "The Effect of Density Ratio on Steep Injection Angle Purge Jet Cooling for a Converging Nozzle Guide Vane Endwall at Transonic Conditions". Thesis, Virginia Tech, 2019. http://hdl.handle.net/10919/102650.

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The study presented herein describes and analyzes a detailed experimental investigation of the effects of density ratio on endwall thermal performance at varying blowing rates for a typical nozzle guide vane platform purge jet cooling scheme. An axisymmetric converging endwall with an upstream doublet staggered cylindrical hole purge jet cooling scheme was employed. Nominal exit flow conditions were engine representative and as follows: {rm Ma}_{Exit} = 0.85, {rm Re}_{Exit,C_{ax}} = 1.5 times {10}^6, and large-scale freestream Tu = 16%. Two blowing ratios were investigated corresponding to the upper and lower engine extrema. Each blowing ratio was investigated amid two density ratios; one representing typical experimental neglect of density ratio, at DR = 1.2, and another engine representative density ratio achieved by mixing foreign gases, DR = 1.95. All tests were conducted on a linear cascade in the Virginia Tech Transonic Blowdown Wind Tunnel using IR thermography and transient data reduction techniques. Oil paint flow visualization techniques were used to gather quantitative information regarding the alteration of endwall flow physics due two different blowing rates of high-density coolant. High resolution endwall adiabatic film cooling effectiveness, Nusselt number, and Net Heat Flux Reduction contour plots were used to analyze the thermal effects. The effect of density is dependent on the coolant blowing rate and varies greatly from the high to low blowing condition. At the low blowing condition better near-hole film cooling performance and heat transfer reduction is facilitated with increasing density. However, high density coolant at low blowing rates isn't adequately equipped to penetrate and suppress secondary flows, leaving the SS and PS largely exposed to high velocity and temperature mainstream gases. Conversely, it is observed that density ratio only marginally affects the high blowing condition, as the momentum effects become increasingly dominant. Overall it is concluded density ratio has a first order impact on the secondary flow alterations and subsequent heat transfer distributions that occur as a result of coolant injection and should be accounted for in purge jet cooling scheme design and analysis. Additionally, the effect of increasing high density coolant blowing rate was analyzed. Oil paint flow visualization indicated that significant secondary flow suppression occurs as a result of increasing the blowing rate of high-density coolant. Endwall adiabatic film cooling effectiveness, Nusselt number, and NHFR comparisons confirm this. Low blowing rate coolant has a more favorable thermal impact in the upstream region of the passage, especially near injection. The low momentum of the coolant is eventually dominated and entrained by secondary flows, providing less effectiveness near PS, near SS, and into the throat of the passage. The high momentum present for the high blowing rate, high-density coolant suppresses these secondary flows and provides enhanced cooling in the throat and in high secondary flow regions. However, the increased turbulence impartation due to lift off has an adverse effect on the heat load in the upstream region of the passage. It is concluded that only marginal gains near the throat of the passage are observed with an increase in high density coolant blowing rate, but severe thermal penalty is observed near the passage onset.
Master of Science

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30

Boháček, Jan. "EFFECT OF FLOW PARAMETERS OF WATER AND AIR ATOMIZED SPRAYS ON COOLING INTENSITY OF HOT SURFACES". Doctoral thesis, Vysoké učení technické v Brně. Fakulta strojního inženýrství, 2011. http://www.nusl.cz/ntk/nusl-233959.

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Práce komplexně popisuje vodní a vodovzdušné chlazení pomocí metod CFD (Computational Fluid Dynamics) konkrétně s využitím software ANSYS FLUENT. Skládá se ze dvou hlavních částí, z nichž první se zabývá numerickým popisem jediné vodní kapky a druhá popisem směsí kapek představující paprsek válcové a ploché trysky. Je založena převážně na vícefázových modelech proudění a vlastních uživatelsky definovaných funkcí (User Defined Functions, UDF) představujících stěžejní část práce. Uvedené výpočtové modely jsou ve většině případů verifikovány pomocí experimentálních dat nebo jiných numerických modelů. V první části práce jsou teoreticky postupně rozebrány všechny tři použité vícefázové modely proudění. První z nich, Volume Of Fluid model (VOF), byl použit pro modelování jediné kapky (mikromodel). Zatímco zbývající dva, Euler-Euler model a Euler-Lagrange model, byly aplikovány v modelu celého paprsku trysky (makromodel). Mikromodel popisuje dynamiku volného pádu vodní kapky. Pro malé průměry kapek (~100µm) standardní model povrchového napětí (Continuum Surface Force, CSF) způsoboval tzv. parazitní proudy. Z toho důvodu je v práci rozebrána problematika výpočtu normál, křivostí volných povrchů a povrchového napětí jako zdroje objemových sil v pohybových rovnicích. Makromodel se zabývá studiem dynamiky celého paprsku tj. oblastí od ústí trysky po dopad na horký povrch, bere v úvahu kompletní geometrii, tzn. např. podpůrné válečky, bramu, spodní část krystalizátoru apod. V práci je rozebrána 2D simulace dopadu paprsku válcové trysky pomocí VOF modelu Euler-Lagrange modelu na horký povrch. Pro případ s VOF modelem byl navržen model blánového varu. Euler-Euler model a Euler-Lagrange model byly využity pro simulaci paprsku ploché trysky horizontálně ostřikující horkou bramu přímo pod krystalizátorem nad první řadou válečků. Pro Euler-Euler model byl navržen model sekundárního rozpadu paprsku založený na teorii nejstabilnější vlnové délky (Blob jet model). Jelikož diskrétní Lagrangeovy částice tvořily v určitých místech spíše kontinuální fázi, byl navržen a otestován model pro konverzi těchto částic do VOF.

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31

Arisi, Allan Nyairo. "Heat Transfer and Flow Characteristics on the Rotor Tip and Endwall Platform Regions in a Transonic Turbine Cascade". Diss., Virginia Tech, 2016. http://hdl.handle.net/10919/64501.

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This dissertation presents a detailed experimental and numerical analysis of the aerothermal characteristics of the turbine extremity regions i.e. the blade tip and endwall regions. The heat transfer and secondary flow characteristics were analyzed for different engine relevant configurations and exit Mach/Reynolds number conditions. The experiments were conducted in a linear blowdown cascade at transonic high turbulence conditions of Mexit ~ 0.85, 0.60 and 1.0, with an inlet turbulence intensity of 16% and 12% for the vane and blade cascade respectively. Transient infrared (IR) thermography technique and surface pressure measurement were used to map out the surface heat transfer coefficient and aerodynamic characteristics. The experiments were complemented with computational modeling using the commercial RANS equation solver ANSYS Fluent. The CFD results provided further insight into the local flow characteristics in order to elucidate the flow physics which govern the measured heat transfer characteristics. The results reveal that the highest heat transfer exists in regions with local flow reattachment and new-boundary layer formation. Conversely, the lowest heat transfer occurs in regions with boundary layer thickening and separation/lift-off flow. However, boundary layer separation results in additional secondary flow vortices, such as the squealer cavity vortices and endwall auxiliary vortex system, which significantly increase the stage aerodynamic losses. Furthermore, these vortices result in a low film-cooling effectiveness as was observed on a squealer tip cavity with purge flow. Finally, the importance of transonic experiments in analyzing the turbine section heat transfer and flow characteristics was underlined by the significant shock-boundary layer interactions that occur at high exit Mach number conditions.
Ph. D.

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32

DeMoss, Joshua Andrew. "Skin Friction and Cross-flow Separation on an Ellipsoidal Body During Constant Yaw Turns and a Pitch-up Maneuver with Roll Oscillation". Diss., Virginia Tech, 2010. http://hdl.handle.net/10919/29063.

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The skin friction and cross-flow separation location on a non-body-of-revolution (non-BOR) ellipsoidal model performing constant-yaw turns and a pitch-up maneuver, each with roll oscillation were studied for the first time. The detailed, low uncertainty, flow topology data provide an extensive experimental database on the flow over non-BOR hull shapes that does not exist anywhere else in the world and serves as a crucial tool for computational validation. The ellipsoidal model was mounted on a roll oscillation machine in the Virginia Tech Stability Wind Tunnel slotted wall test section. Hot-film sensors with constant temperature anemometers provided skin friction magnitudes on the body's surface for thirty-three steady flow model orientations and three unsteady maneuvers at a constant Reynolds number of 2.5 million. Cross-flow separation locations on the model were determined from span-wise minima in the skin friction magnitude for both the steady orientations and unsteady maneuvers. Steady hot-film data were obtained over roll angles between Â±25Â° in 5Â° increments with the model mounted at 10Â° and 15Â° yaw and at 7Â° pitch with respect to the flow. The roll oscillation machine was used to create a near sinusoidal unsteady roll motion between Â±26Â° at a rate of 3 Hz, which corresponded to a non-dimensional roll period of 5.4. Unsteady data were obtained with the ellipsoidal model mounted at 10Â° and 15Â° yaw and at 7Â° pitch during the rolling maneuver. Cross-flow separation was found to dominate the leeside flow of the model for all orientations. For the yaw cases, the separation location moved progressively more windward and inboard as the flow traveled downstream. Increasing the model roll or yaw angle increased the adverse pressure gradient on the leeward side, creating stronger cross-flow separation that began further upstream and migrated further windward on the model surface. For the pitch flow case, the cross-flow separation remained straight as the flow moved axially downstream. The strongest pitch cross-flow separation was observed at the most negative roll angle and dissipated, moving further downstream and inboard as the modelâ s roll angle was increased. The unsteady flow maneuvers exhibited the same flow topology observed in the quasi-steady conditions. However, the unsteady skin friction and separation locations lagged their quasi-steady counterparts at equivalent roll angles during the oscillation cycle. A first order time lag model and sinusoidal fit to the separation location data quantified the time lags that were observed.
Ph. D.

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33

Araújo, Gomes Reinaldo [Verfasser], Reinhard [Akademischer Betreuer] Niehuis y Dietmar [Akademischer Betreuer] Hennecke. "On Aerothermal Effects of Film Cooling on Turbine Blades with Flow Separation / Reinaldo Araújo Gomes. Reinhard Niehuis. Dietmar Hennecke. Universität der Bundeswehr München, Fakultät für Luft- und Raumfahrttechnik". Neubiberg : Universitätsbibliothek der Universität der Bundeswehr, 2010. http://d-nb.info/1005897514/34.

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34

Boccaletto, Luca. "Maîtrise du décollement de tuyère. Analyse du comportement d'une tuyère de type TOC et définition d'un nouveau concept : le BOCCAJET". Thesis, Aix-Marseille 1, 2011. http://www.theses.fr/2011AIX10012/document.

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Cette recherche s’articule en deux parties. L’objectif de la première partie est d’analyser par voie expérimentale et numérique la phénoménologie du décollement interne, dit décollement de jet (en regimes transitoire et établi) dans les tuyères supersoniques refroidies par film fluide. La deuxième partie porte sur la réinterprétation des concepts de tuyère existants pour aboutir à la proposition d’un nouveau dispositif de détente supersonique, qui offre une résistance accrue au décollement de jet. La première partie de cette thèse est basée sur l’analyse des résultats expérimentaux obtenus lors de la campagne d’essais réalisée à l’ONERA. Ces essais, ont mis en évidence des spécificités de comportement de la tuyère, inhérentes à la manière d’amorcer le jet supersonique principal par rapport à l’établissement du film pariétal. Ces mêmes expériences ont permis d’étudier le comportement instationnaire du décollement de jet lorsque les conditions d’alimentation sont maintenues en régime établi. L’apparition de fréquences caractéristiques a été mise en évidence et leur origine a été étudiée à l’aide de simulations numériques. En nous appuyant sur les considérations issues de la première partie de l’étude, une revue critique des concepts de tuyère existants a été menée. Ce travail a permis d’identifier une lacune majeure dans la définition des tuyères à écoulement interne, à savoir l’absence d’une « barrière » qui puisse prévenir l’occurrence du décollement de jet. Ainsi, nous avons proposé la conjonction d’un dispositif à écoulement externe (aerospike) et d’une tuyère classique afin de résoudre cette problématique in nuce, en créant une barrière fluidique continue tout autour du plan de sortie de la tuyère principale. L’efficacité de ce concept a donc été prouvée par calcul, puis une campagne expérimentale a été organisée afin de valider les résultats obtenus
This research is in two parts. The objective of the first part is to analyse by experimental and numerical means the phenomenology of nozzle flow separation in transient and steady state conditions. The second part of this research work focuses on the reinterpretation of existing concepts of converging-diverging nozzles, leading to the proposal of a new supersonic expansion device, with improved flow separation characteristics.Experimental data, collected during the test campaign conducted at ONERA, have been analysed and are presented in the first part of this thesis. Obtained results highlight some peculiarities of the transient behavior of the nozzle, mostly dependent on the synchronisation between the start-up phase of the main jet and the grow-up of the wall film. These same experiments have been also used to investigate the unsteadiness of the flow separation, when nozzle feeding conditions are maintained constant. Appearance of characteristic frequencies has been highlighted and their origin has been investigated by CFD simulations.In the second part, a critical review of existing nozzle concepts was conducted. This allowed identifying a major gap in the definition of traditional supersonic nozzles, namely the absence of a "barrier" that can prevent the occurrence of the flow separation. Thus, in the second part of this thesis we propose a new nozzle concept. It is based on the combination of a small aerospike and a conventional nozzle (main flow). Such an arrangement allows solving the flow separation problem in nuce. The effectiveness of this concept has been proved by calculation and by an experimental test campaign

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35

Trigell, Emelie. "CFD-simulations of urea-waterspray in an after-treatment systemusing Star-CCM+". Thesis, KTH, Mekanik, 2018. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-250015.

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The legislation has forced the vehicle industry to reduce tail-end emissions. The air pollutant nitrogen oxide (NOX) has been shown to have a negative impact on human health and the environment. One of the key technologies to reduce the levels of NOX emitted from a vehicle is by implementing an after-treatment system. The after-treatment system includes catalysts, a particle filter and an evaporation system. In the evaporation system a liquid jet containing a urea-water solution known as AdBlue is injected into the hot exhaust gases to evaporate into gaseous ammonia NH3 and water H2O. Then NH3 enters the Selective Catalytic Reduction (SCR) catalyst where it chemically reacts with NOX to form N2 and H2O. Problems can arise if an excessive amount of AdBlue is injected and a fluid film is formed on evaporation surfaces. At certain operating conditions the fluid film can crystallise and form solid deposits. The solid deposits can cause high back-pressure, material deterioration and ammonia slip. This project is done in collaboration with Scania CV AB. Scania is a world-leading manufacturer of heavy-duty vehicles, busses and engines. Scania works continuously to develop new simulation methods to capture the complex phenomena of AdBlue spray, wall film dynamics and risk of solid deposits, to use in the development process of new components. The aim of this project is to implement and evaluate a new method to predict the risk of crystallisation of urea (AdBlue) using the software Star-CCM+. Two different geometries are studied, a test rig and a Scania silencer. Different operating conditions, parameter settings and a speed-up method are analysed. During the project a base-line model has been created and the results have been compared with measurement results and the software AVL Fire. The results on the test rig show the effect of altering the mesh and important model parameters. Injected particles are grouped into parcels with the same properties. The number of parcels is a crucial factor for the wall film formation and should be sufficiently high to get a statistical representation of the droplet size distribution. The results from the real silencer show strong evaporation and thin wall film formation with the suggested method. The method is shown to be stable and the software is user-friendly. A speed-up method was investigated to decrease the computational time. The computational time was reduced by a factor 20. The outcome of this project is a guide for set-up of AdBlue spray and wall film simulations. Recommendations to future work includes further validation of the settings, investigation of the evaporation rate and droplet size distribution and the application to other cases. The next step is also to tune the critical thresholds for deposit risk assessment.
Lagstiftning har tvingat fordonstillverkare att minska avgasutsläppen. Luftföroreningen kväveoxid (NOX) har visat sig ha en negativ inverkan på människors hälsa och på miljön. En viktig teknik för att minska utsläppen av NOX ¨ar att implementera ett efterbehandlingssystem. Efterbehandlingssystemet tar hand om avgaserna genom substrat, filter och ett förångningssystem. I förångningssystemet sprutas en urea-vattenlösning, som kallas AdBlue, in i de heta avgaserna där den förångas till ammoniak NH3 och vatten H2O. Ammoniakgasen leds därefter in till SCR katalysatorn där den kemiskt reagerar med NOX och bildar kvävgas N2 och vattenånga. Problem kan uppstå om fel mängd AdBlue sprutas in, då kan vätska byggas upp på förångsningsytor, kristallisera och bilda avlagringar. Avlagringarna kan bygga upp en solid klump som kan orsaka ett högt mottryck, nedbrytning av material och ammoniakslip. Detta arbete är ett samarbete med Scania CV AB som är en världsledande producent av lastbilar, bussar och motorer. Scania arbetar kontinuerligt med att utveckla nya simuleringsvertyg för att beskriva uppkomsten av Urea avlagringar för att använda i utvecklingen av nya komponenter. Syftet med detta arbete är att implementera och utvärdera en ny metod för att prediktera klump mha simuleringsverktyget Star-CCM+. Två olika geometrier är använd i arbetet: en testrigg och en av Scanias ljuddämpare. Olika driftspunkter, parametrar och en uppsnabbad metod är studerade. Under projektets gång har en modell byggts upp och jämförts med mätningar och simuleringar från programvaran AVL Fire. Resultatet från simuleringarna på testriggen visar effekten av att variera olika parametrar. Partiklarna som sprutas in i systemet är grupperade i paket med liknande egenskaper. Antalet paket påverkar uppbyggnaden av väggfilm och det rekommenderas att denna parameter hålls hög för att statistiskt beskriva droppfördelningen av partiklar. Resultaten på ljuddämparen visar en stark förångning och en tunn väggfilm för samtliga driftspunkter. Den implementerade metoden har visat sig vara stabil och användarvänlig. En uppsnabbad metod har utvärderats för att minska beräkningstiden. Beräkningstiden kunde minskas med en faktor 20. Resultatet av arbetet är en guide för hur metoden implementeras och bör användas. Rekommendationer till framtida arbete är en fortsatt undersökning av parametrar, utvärdering av förångningsmodellen, validering av droppstorleksfördelningen och tillämpningen på andra geometrier. Nästa steg i utvecklingen skulle vara att kalibrera tröskelvärden för prediktering av klump.

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36

O'Dowd, Devin Owen. "Aero-thermal performance of transonic high-pressure turbine blade tips". Thesis, University of Oxford, 2010. http://ora.ox.ac.uk/objects/uuid:e7b8e7d0-4973-4757-b4df-415723e7562f.

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37

Li, Shiou-Jiuan. "Experimental Investigation of Film Cooling Effectiveness on Gas Turbine Blades". Thesis, 2012. http://hdl.handle.net/1969.1/148288.

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High turbine inlet temperature becomes necessary for increasing thermal efficiency of modern gas turbines. To prevent failure of turbine components, advance cooling technologies have been applied to different portions of turbine blades. The detailed film cooling effectiveness distributions along a rotor blade has been studied under combined effects of upstream trailing edge unsteady wake with coolant ejection by the pressure sensitive paint (PSP). The experiment is conducted in a low speed wind tunnel with a five blade linear cascade and exit Reynolds number is 370,000. The density ratios for both blade and trailing edge coolant ejection range from 1.5 to 2.0. Blade blowing ratios are 0.5 and 1.0 on suction surface and 1.0 and 2.0 on pressure surface. Trailing edge jet blowing ratio and Strouhal number are 1.0 and 0.12, respectively. Results show the unsteady wake reduces overall effectiveness. However, the unsteady wake with trailing edge coolant ejection enhances overall effectiveness. Results also show that the overall effectiveness increases by using heavier coolant for ejection and blade film cooling. Leading edge film cooling has been investigated using PSP. There are two test models: seven and three-row of film holes for simulating vane and blade, respectively. Four film holes’ configurations are used for both models: radial angle cylindrical holes, compound angle cylindrical holes, radial angle shaped holes, and compound angle shaped holes. Density ratios are 1.0 to 2.0 while blowing ratios are 0.5 to 1.5. Experiments were conducted in a low speed wind tunnel with Reynolds number 100,900. The turbulence intensity near test model is about 7%. The results show the shaped holes have overall higher effectiveness than cylindrical holes for both designs. As increasing density ratio, density effect on shaped holes becomes evident. Radial angle holes perform better than compound angle holes as increasing blowing and density ratios. Increasing density ratio generally increases overall effectiveness for all configurations and blowing ratios. One exception occurs for compound angle and radial angle shaped hole of three-row design at lower blowing ratio. Effectiveness along stagnation row reduces as increasing density ratio due to coolant jet with insufficient momentum caused by heavier density coolant, shaped hole, and stagnation row.

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38

Li, Haoming. "The Counter-Rotating Vortex Pair in Film-Cooling Flow and its Effect on Cooling Effectiveness". Thesis, 2011. http://spectrum.library.concordia.ca/36295/1/Li_MSc_F2011.pdf.

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A fundamental investigation on a key vortical structure in film cooling flow, which is called counter-rotating vortex pair (CRVP), has been performed. Traditionally, the coolant’s momentum flux ratio is thought as the most critical parameter on film cooling effectiveness, which is the index of film cooling performance, and this performance is also influenced notably by CRVP. About the sources of CRVP, the in-tube vortex, the in-tube boundary layer vorticity, the jet/mainstream interaction effect, alone or combined, are proposed as the main source in the literature. A numerical approach was applied in present study. By simulating a general inclined cylindrical cooling hole on a flat plate (the baseline case), the CRVP was visualized as well as the in-tube vortex. Another case, which is identical with the baseline except the boundary condition of the in-tube wall was set as free-slip to isolate its boundary layer effect, was simulated for comparing. Their comparisons have clarified that the jet/mainstream interaction is the only essential source of CRVP. Through further analyzing its mechanism, CRVP was found to be a pair of x direction (mainstream wise direction) vortices. Hence, the velocity gradients -v/z and w/y were the promoters of CRVP. Applying this mechanism, a new scheme named nozzle scheme was designed to control the CRVP intensity and isolate the overall momentum flux ratio Iov, a parameter used in literature. Analysis of the effects of CRVP intensity and momentum flux ratio on film cooling effectiveness has demonstrated that the CRVP intensity, instead of the momentum flux ratio, was the most critical factor governing the film cooling performance.

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39

Lee, Jian-shine y 李建興. "Numerical analyses on film cooling under spray combustion flow of an afterburner". Thesis, 2007. http://ndltd.ncl.edu.tw/handle/45663962570976022966.

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碩士
國立成功大學
航空太空工程學系碩博士班
95
The afterburner is usually operated under the high-speed and high-temperature conditions. In order to reduce the costly experimental attempts for parameter analyses, a simulation model was proposed to investigate the combustion and heat transfer phenomena in the flow field of the afterburner. In this study, the interaction of flow-field variation and liner under spray combustion was calculated by the simulation model. The results shown that the variation of liner leaded to different cooling effect. In this study, the different inlet velocities of cooling flow were applied. Consequently, the effects of different slot liners were also discussed. The results indicated that the faster cooling flow velocity and wider liner slot leaded to better cooling performance. The model proposed by this study, which takes into account the flame holder, liner those in spray combustion, and operation under the conditions similar to the real afterburner, can be utilized as an auxiliary tool to the experimental investigation.

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40

Zheng, Yingjie. "A Flow Field Study of a Film Cooling Hole Featuring an Orifice". Thesis, 2013. http://spectrum.library.concordia.ca/978113/1/Zheng_MASc_S2014.pdf.

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Film cooling is a jet-in-crossflow application in gas turbines used to protect high temperature parts. Understanding the physical phenomena in the flow field, for example the detrimental counter-rotating vortex pair, is highly critical. Experimental investigations were conducted using stereoscopic PIV to study the flow field downstream from film cooling holes featuring an orifice, under blowing ratios from 0.5 to 2.0. The original geometry of a short injection hole that was proposed in a previous numerical study was examined. The results reported a significant reduction in counter-rotating vortex pair strength of nozzle hole injection in comparison with cylindrical hole injection. The streamwise vorticity of the nozzle hole jet averaged a drop of 55% at a low blowing ratio of 0.5, and a 30%–40% drop at high blowing ratios of 1.0, 1.5 and 2.0. Due to the reduction in counter-rotating vortex pair strength, a round jet bulk was observed forming from the two legs of a typical kidney-shaped jet. The merged jet bulk delivered better coverage over the surface. The effect of the geometrical parameters of the orifice and the effect of the blowing ratio were also investigated using long injection hole geometry to isolate the impact of the short hole length. It was found that under high blowing ratio conditions, no structural difference occurred in the jet when altering the value of blowing ratio. The most important geometrical parameters were the opening width and the in-hole position of the orifice. The measurement results suggested that the width of the orifice had a major impact on downstream counter-rotating vortex pair strength, and the in-hole position of the orifice mainly affected the penetration characteristics of the jet. The mechanism of the counter-rotating vortex suppressing effect of the orifice was studied from the flow field data. It is proven that the orifice greatly eliminated the hanging vortices developing from the in-hole boundary layer vorticity, which was the major contributor to counter-rotating vortex formation in inclined jets.

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41

Sriram, R. "Investigations On Film Cooling At Hypersonic Mach Number Using Forward Facing Injection From Micro-Jet Array". Thesis, 2008. http://hdl.handle.net/2005/763.

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A body in a hypersonic flow field will experience very high heating especially during re-entry. Conventionally this problem is tackled to some extent by the use of large angle blunt cones. At the cost of increased drag, the heat transfer rate is lower over most parts of the blunt body, except in a region around the stagnation point. Thus even with blunt cones, management of heat transfer rates and drag on bodies at hypersonic speeds continues to be an interesting research area. Various thermal protection systems have been proposed in the past, like heat sink cooling, ablation cooling and aerospikes. The ablative cooling system becomes extremely costly when reusability is the major concern. Also the shape change due to ablation can lead to issues with the vehicle control. The aerospikes themselves may become hot and ablate at hypersonic speeds. Hence an alternate form of cooling system is necessary for hypersonic flows, which is more feasible, cost effective and efficient than the conventional cooling systems. Injection of a mass of cold fluid into the boundary layer through the surface is one of the potential cooling techniques in the hypersonic flight corridors. These kinds of thermal protection systems are called mass transfer cooling systems. The injection of the mass may be through discrete slots or through a porous media. When the coolant is injected through a porous media over the entire surface, the coolant comes out as a continuous mass. Such a cooling system is also referred as “transpiration cooling system”. When the fluid is injected through discrete slots, the system is called as “film cooling system”. In either case, the coolant absorbs the incoming heat through its rise in enthalpy and thus modifies the boundary layer characteristics in such a way that the heat flow rate to the surface is less. Injection of a forward facing jet (opposite to the freestream direction) from the stagnation point of a blunt body can be used for mitigating both the aerodynamic drag and heat transfer rates at hypersonic Mach numbers. If the jet has enough momentum it can push the bow shock forward, resulting in reduced drag. This will also reduce heat transfer rate over most part of the body except around the jet re-attachment region. A reattachment shock impinging on the blunt body invariably increases the local heat flux. At lower momentum fluxes the forward facing jet cannot push the bow shock ahead of the blunt body and spreads easily over the boundary layer, resulting in reduced heat transfer rates. While the film cooling performance improves with mass flow rate of the jet, higher momentum flow rates can lead to a stronger reattachment leading to higher heat transfer rate at the reattachment zone. If we are able to reduce the momentum flux of the coolant for the same mass flow rate, the gas coming out can easily spread over the boundary layer and it is possible to improve the film cooling performance. In all the reported literature, the mass flow rate and the momentum flux are not varied independently. This means, if the mass flow rate is increased, there is a corresponding increase in the momentum flux. This is because the injection (from a particular orifice and for a particular coolant gas) is controlled only by the total pressure of injection and free stream conditions. The present investigation is mainly aimed at demonstrating the effect of reduction in momentum of the coolant (injected opposing a hypersonic freestream from the stagnation point of a blunt cone), keeping the mass flow rate the same, on the film cooling performance. This is achieved by splitting a single jet into a number of smaller jets of same injection area (for same injection total pressure and same free stream conditions). To the best of our knowledge there is no report on the use of forward facing micro-jet array for film cooling at hypersonic Mach numbers. In this backdrop the main objectives of the present study are: • To experimentally demonstrate the effect of splitting a single jet into an array of closely spaced smaller micro-jets of same effective area of injection (injected opposite to a hypersonic freestream from the stagnation zone), on the reduction in surface heat transfer rates on a large angle blunt cone. · Identifying various parameters that affect the flow phenomenon and doing a systematic investigation of the effect of the different parameters on the surface heat transfer rates and drag. Experimental investigations are carried out in the IISc hypersonic shock tunnel on the film cooling effectiveness. Coolant gas (nitrogen and helium) is injected opposing hypersonic freestream as a single jet (diameter 2 mm and 0.9 mm), and as an array of iv micro jets (diameter 300 micron each) of same effective area (corresponding to the respective single jet). The coolant gas is injected from the stagnation zone of a blunt cone model (58o apex angle and nose radius of 35 mm). Experiments are performed at a flow freestream Mach number of 5.9 at 0o angle of attack, with a stagnation enthalpy of 1.84 MJ/Kg, with and without injections. The ratios of the jet stagnation pressure to the pitot pressure (stagnation pressure ratio) used in the present study are 1.2 and 1.45. Surface convective heat transfer measurements using platinum thin film sensors, time resolved schlieren flow visualization and aerodynamic drag measurements using accelerometer force balance are used as flow diagnostics in the present study. The theoretical stagnation point heat transfer rate without injection for the given freestream conditions for the test model is 79 W/cm2 and the corresponding aerodynamic drag from Newtonian theory is 143 N. The measured drag value without injection (125 N) shows a reasonable match with theory. As the injection is from stagnation zone it is not possible to measure the surface heat transfer rates at the stagnation point. The sensors thus are placed from the nearest possible location from the stagnation point (from 16 mm from stagnation point on the surface). The sensors near the stagnation point measures a heat transfer rate of 65 W/cm2 on an average without any injection. Some of the important conclusions from the study are: • Up to 40% reduction in surface heat transfer rate has been measured near the stagnation point with the array of micro jets, nitrogen being the coolant, while the corresponding reduction was up to 30% for helium injection. Considering the single jet injection, near the stagnation point there is either no reduction in heat transfer rate or a slight increase up to 10%. · Far away from stagnation point the reduction in heat transfer with array of micro-jets is only slightly higher than corresponding single jet for the same pressure ratio. Thus the cooling performance of the array of closely spaced micro jets is better than the corresponding single jet almost over the entire surface. • The time resolved flow visualization studies show no major change in the shock standoff distance with the low momentum gas injection, indicating no major changes in other aerodynamic aspects such as drag. · The drag measurements also indicate that there is virtually no change in the overall aerodynamic drag with gas injection from the micro-orifice array. · The spreading of the jets injected from the closely spaced micro-orifice array over the surface is also seen in the visualization, indicating the absence of a region of strong reattachment. · The reduction in momentum flux of the injected mass due to the interaction between individual jets in the case of closely spaced micro-jet array appears to be the main reason for better performance when compared to a single jet. The thesis is organized in six chapters. The importance of film cooling at hypersonic speeds and the objectives of the investigation are concisely presented in Chapter 1. From the knowledge of the flow field with counter-flow injection obtained from the literature, the important variables governing the flow phenomena are organized as non-dimensional parameters using dimensional analysis in Chapter 2. The description of the shock tunnel facility, diagnostics and the test model used in the present study is given in Chapter 3. Chapter 4 describes the results of drag measurements and flow visualization studies. The heat transfer measurements and the observed trends in heat transfer rates with and without coolant injection are then discussed in detail in Chapter 5. Based on the obtained results the possible physical picture of the flow field is discussed in Chapter 6, followed by the important conclusions of the investigation.

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42

Hassan, Othman. "Thermal and Flow Field Investigations of a Micro-Tangential-Jet Film Cooling Scheme on Gas Turbine Components". Thesis, 2013. http://spectrum.library.concordia.ca/977393/1/Hassan_PhD_F2013.pdf.

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Thermal and Flow Field Investigations of a Micro-Tangential-Jet Film Cooling Scheme on Gas Turbine Components Othman Hassan, Ph.D. Concordia University, 2013 Gas turbines play a major role in modern aerospace and in industrial power generation nowadays. Advanced gas turbines are designed to operate at increasingly higher inlet turbine gas temperature to increase their efficiency and specific power output. In order to enable this increase in the operating temperature, high-temperature resistant materials, Thermal-Barrier Coatings (TBCs), and advanced cooling techniques, are employed. Internal cooling, impingement cooling, and film cooling, are the typical cooling techniques that are being used nowadays for gas turbine engines cooling. For the past five decades, significant efforts have been implemented in the area of film cooling to design and investigate the performance of numerous cooling schemes at various operating conditions and geometries. However, the achieved effectiveness to date, especially over actual airfoil geometries, is still relatively low. Further efforts are essential to propose novel designs that are capable of providing the required cooling loads. The present study investigates the thermal performance and flow characteristics downstream a new film cooling scheme over a gas turbine vane and a flat plate. The state-of-the-art transient Thermochromic Liquid Crystal (TLC) technique has been employed for film cooling measurements, while the Particle Image Velocimetry (PIV) technique has been employed for flow field investigations. Validation of all measurement techniques were conducted and good agreement with literature works has been achieved. The Micro-Tangential-Jet (MTJ) scheme is a discrete-holes shaped cooling scheme with micro sized exit height that supplies the jet parallel to the surface. The MTJ scheme consists of two main parts, a circular supply micro-tube, and a shaped exit parallel to the vane surface. The shaped exit of the scheme starts with a circular cross section. Lateral expansion angles are then applied in both directions and a relatively constant height is maintained throughout the scheme yielding a squared exit. Due to the micro thickness of the jet, a deep penetration inside the main stream is achievable, while maintaining a tangential injection direction to the surface, thereby avoiding jet lift off. The film cooling performance of one row of MTJ scheme on the vane pressure side and another row on the suction side is investigated at different blowing ratios using the transient TLC technique. Comparisons with the film cooling performance of previously proposed shaped schemes are carried out to highlight the advantages and disadvantages of the new design. Mach number distributions over the airfoil surface are determined with and without the MTJ scheme to investigate the effect of the added material on the airfoil characteristics. A comprehensive analysis based on the current findings, previous efforts in the literature, and the flow field investigations using the PIV technique downstream the MTJ scheme is presented. Overall, the new design showed superior film cooling performance, compared to the best achieved results in literature. The effectiveness distribution downstream the MTJ scheme was characterized with superior lateral spreading over both pressure and suction surfaces. The measurements showed similarity in the characteristics of the 2-D film downstream the MTJ scheme and the one that accompanies the injection from continuous slot schemes. Moreover, the investigations showed that the presence of the MTJ scheme over the vane pressure or suction sides did not result in significant HTC augmentation, especially at blowing ratios less than unity. The MTJ scheme could be the first of a new generation of film cooling schemes over airfoil geometries.

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43

Chang, Shun-Fu y 張順富. "An Experimental Study of Heat Transfer and Effectiveness on the Endwall of a Vane Passage Using Paired Film Cooling Flow Impinging to Each Other". Thesis, 2006. http://ndltd.ncl.edu.tw/handle/12763347164552777971.

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碩士
大葉大學
機械工程研究所碩士班
94
This research concerns about a new film cooling technique and the feasibility of its application to the protection of the endwall in a vane passage. This new technique utilizes pairs of coolant jets impinging against each other to form more aggregated and more uniform distribution of the film cooling effectiveness. The experimental results by using this technique are compared to those with parallel jets at the same coolant flow rate, endwall entrance condition, and the blowing ratio. In the experiments, the endwall of a vane passage was tested. Liquid crystal thermography was employed to measuring the distributions of local heat transfer coefficient（HTC）and film cooling effectiveness. The Reynolds number of the main flow was fixed at . The blowing ratio was set be 0.5, 1.0, 2.0. The investigated entrance conditions include a smooth endwall, an endwall with a forward-facing entrance step, and an endwall with a backward-facing step. 　　Results show that the pattern of the HTC distribution could be altered by the overall arrangement of the cooling holes. However, the HTC values did not change much. In the case of film cooling, the new technique with offset impinging cooling jets provides longer coverage area by the coolant, and the protected region is shifted towards the suction wall. This new technique is less sensitive to the blowing ratio and the entrance condition of the endwall compared to the design with parallel coolant jets. Hence, it is a better technique.

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44

Chien, Chia-hung y 簡嘉宏. "Application of the CFD method to Thin Liquid Film Flow between Two Forward and Reversed Rollers and Thermal-Hydraulic Analysis of Water Cooling Channel for a High Speed Spindle". Thesis, 2008. http://ndltd.ncl.edu.tw/handle/56570792049605231454.

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博士
國立成功大學
機械工程學系碩博士班
96
In this study the three dimensional non-Newtonian flow in forward and reversed roll coating process had been studied by both experimental and numerical simulations. The non-Newtonian behavior of the coating fluid had also been accounted using Ostwald’s power law model with power index values of n = 0.95, 1.05 and 1.15. Experiments were conducted on three roll coating system of pick up roll , applicator roll and panel roll with non-Newtonian coating fluid. In the forward and reversed coating, the gap between two rollers was maintained at 100 and 25 μm, respectively. The coating film thickness were measured during the experiments. In the forward coating process, the speed ratio was the most important factor which affects the coating film thickness. The results shown that the distance from nip point to film splitting point and the film thickness on the application roll increases with increasing roll speed ratio, but the film thickness on pick up roll decreases with increasing roll speed ratio. Comparison of experimental results and numerical simulation results shown that the numerical computations over predict the coating film thickness and error between the experimental and numerical results being 5-10%. In the reversed coating process, it was found that as the speed ratio was increased, the transferred film thickness was reduced, while the leakage film thickness was increased. As the power index was increased, the transferred film thickness was increased, while the leakage film thickness was decreased and the film splitting point moves further away from the gap centre between two rolls. The pressure distribution increases with rising the power-law index. It was also shown that dilatant fluid (n>1) exhibits ribbing instability with more waviness on the film surface. In addition, this study also used numerically and experimentally analyze the three-dimensional fluid motion and temperature distributions in a built-in motorized high-speed spindle with a helical water cooling channel. The effects of different heat sources and cooling water flow rate were examined in detail. The results indicated that almost all the hot spots were concentrated near the center of the spindle axis, and temperature increase can be significantly reduced with helical water-cooling. The predicted temperature distribution of the spindle housing was in good agreement with the result obtained from experiments. It was also shown that the heat transfer coefficient h varies with V 0.184. Regression analysis was conducted to obtain Nu =4.63 Re 0.184, which can be applied for 5 x 10 4 < Re < 1.5 x 105 .

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45

Mosberg, Noah Avram. "Experimental investigation of the performance of a fully cooled gas turbine vane with and without mainstream flow and experimental analysis supporting the redesign of a wind tunnel test section". Thesis, 2013. http://hdl.handle.net/2152/28499.

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This study focused on experimentally determining the cooling performance of a fully cooled, scaled-up model of a C3X turbine vane. The primary objective was to determine the differences in overall effectiveness in the presence and absence of a hot mainstream flowing over the vane. Overall effectiveness was measured using a thermally scaled matched Biot number vane with an impingement plate providing the internal cooling. This is the first study focused on investigating the effect of removing the mainstream flow and comparing the contour and laterally-averaged effectiveness data in support of the development of an assembly line thermal testing method. It was found that the proposed method of factory floor testing of turbine component cooling performance did not provide comparable information to traditional overall effectiveness test methods. A second experiment was performed in which the effect of altering the angle of attack of a flow into a passive turbulence generator was investigated. Measurements in the approach flow were taken using a single wire hot-wire anemometer. This study was the first to investigate the effects such a setup would have on fluctuating flow quantitates such as turbulence intensity and integral length scale rather than simply the mean quantities. It was found that both the downstream turbulence intensity and the turbulence integral length scale increase monotonically with approach flow incidence angle at a specified distance downstream of the turbulence generator.
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Tesis sobre el tema "Unsteady flow on film cooling"

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