Artículos de revistas: "Unsteady flow on film cooling"

1

Martini, P., A. Schulz, H. J. Bauer y C. F. Whitney. "Detached Eddy Simulation of Film Cooling Performance on the Trailing Edge Cutback of Gas Turbine Airfoils". Journal of Turbomachinery 128, n.º 2 (1 de febrero de 2005): 292–99. http://dx.doi.org/10.1115/1.2137739.

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The present study deals with the unsteady flow simulation of trailing edge film cooling on the pressure side cut back of gas turbine airfoils. Before being ejected tangentially on the inclined cut-back surface, the coolant air passes a partly converging passage that is equipped with turbulators such as pin fins and ribs. The film mixing process on the cut back is complicated. In the near slot region, due to the turbulators and the blunt pressure side lip, turbulence is expected to be anisotropic. Furthermore, unsteady flow phenomena like vortex shedding from the pressure side lip might influence the mixing process (i.e., the film cooling effectiveness on the cut-back surface). In the current study, three different internal cooling designs are numerically investigated starting from the steady RaNS solution, and ending with unsteady detached eddy simulations (DES). Blowing ratios M=0.5; 0.8; 1.1 are considered. To obtain both, film cooling effectiveness as well as heat transfer coefficients on the cut-back surface, the simulations are performed using adiabatic and diabatic wall boundary conditions. The DES simulations give a detailed insight into the unsteady film mixing process on the trailing edge cut back, which is indeed influenced by vortex shedding from the pressure side lip. Furthermore, the time averaged DES results show very good agreement with the experimental data in terms of film cooling effectiveness and heat transfer coefficients.

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2

Abhari, R. S. "Impact of Rotor–Stator Interaction on Turbine Blade Film Cooling". Journal of Turbomachinery 118, n.º 1 (1 de enero de 1996): 123–33. http://dx.doi.org/10.1115/1.2836593.

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The goal of this study is to quantify the impact of rotor–stator interaction on surface heat transfer of film cooled turbine blades. In Section I, a steady-state injection model of the film cooling is incorporated into a two-dimensional, thin shear layer, multiblade row CFD code. This injection model accounts for the penetration and spreading of the coolant jet, as well as the entrainment of the boundary layer fluid by the coolant. The code is validated, in the steady state, by comparing its predictions to data from a blade tested in linear cascade. In Section II, time-resolved film cooled turbine rotor heat transfer measurements are compared with numerical predictions. Data were taken on a fully film cooled blade in a transonic, high pressure ratio, single-stage turbine in a short duration turbine test facility, which simulates full-engine nondimensional conditions. Film cooled heat flux on the pressure surface is predicted to be as much as a factor of two higher in the time average of the unsteady calculations compared to the steady-state case. Time-resolved film cooled heat transfer comparison of data to prediction at two spanwise positions is used to validate the numerical code. The unsteady stator–rotor interaction results in the pulsation of the coolant injection flow out of the film holes with large-scale fluctuations. The combination of pulsating coolant flow and the interaction of the coolant with this unsteady external flow is shown to lower the local pressure side adiabatic film effectiveness by as much as 64 percent when compared to the steady-state case.

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3

Lenzi, Tommaso, Alessio Picchi, Tommaso Bacci, Antonio Andreini y Bruno Facchini. "Unsteady Flow Field Characterization of Effusion Cooling Systems with Swirling Main Flow: Comparison Between Cylindrical and Shaped Holes". Energies 13, n.º 19 (23 de septiembre de 2020): 4993. http://dx.doi.org/10.3390/en13194993.

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The presence of injectors with strongly swirled flows, used to promote flame stability in the combustion chambers of gas turbines, influences the behaviour of the effusion cooling jets and consequently of the liner’s cooling capabilities. For this reason, unsteady behaviour of the jets in the presence of swirling flow requires a characterization by means of experimental flow field analyses. The experimental setup of this work consists of a non-reactive single-sector linear combustor test rig, scaled up with respect to the real engine geometry to increase spatial resolution and to reduce the frequencies of the unsteadiness. It is equipped with a radial swirler and multi-perforated effusion plates to simulate the liner cooling system. Two effusion plates were tested and compared: with cylindrical and with laid-back fan-shaped 7-7-7 holes in staggered arrangement. Time resolved Particle Image Velocimetry has been carried out: the unsteady characteristics of the jets, promoted by the intermittent interactions with the turbulent mainstream, have been investigated as their vortex structures and turbulent decay. The results demonstrate how an unsteady analysis is necessary to provide a complete characterization of the coolant behaviour and of its turbulent mixing with mainflow, which affect, in turn, the film cooling capability and liner’s lifetime.

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4

Baek, Seung y Savas Yavuzkurt. "Effects of Flow Oscillations in the Mainstream on Film Cooling". Inventions 3, n.º 4 (24 de octubre de 2018): 73. http://dx.doi.org/10.3390/inventions3040073.

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The objective of this study is to investigate the effects of oscillations in the main flow and the coolant jets on film cooling at various frequencies (0 to 2144 Hz) at low and high average blowing ratios. Numerical simulations are performed using LES Smagorinsky–Lilly turbulence model for calculation of the adiabatic film cooling effectiveness and using the DES Realizable k-epsilon turbulence model for obtaining the Stanton number ratios (St/Sto). Additionally, multi-frequency inlet velocities are applied to the main and coolant flows to explore the effects of multi-frequency unsteady flows and the results are compared to those at single frequencies. The results show that at a low average blowing ratio (M = 0.5) if the oscillation frequency is increased from 0 to 180 Hz, the effectiveness decreases and the Stanton number ratio increases. However, when the frequency goes from 180 to 268 Hz, the effectiveness sharply increases and the Stanton number ratio increases slightly. If the frequency changes from 268 to 1072 Hz, the film cooling effectiveness decreases and the Stanton number ratio increases slightly. If the frequency goes from 1072 to 2144 Hz, the film cooling effectiveness climbs up and the Stanton number ratio decreases. The results show that at high average blowing ratio (M = 1.0) the trends of the film cooling effectiveness are similar to those at low blowing ratio (M = 0.5) except from 0 to 90 Hz. If the frequency goes from 0 to 90 Hz at M = 1.0, the film cooling effectiveness increases and the Stanton number ratio decreases. It can be said that it is important to include the effects of oscillating flows when designing film cooling systems for a gas turbine.

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5

Han, Je-Chin. "Recent Studies in Turbine Blade Cooling". International Journal of Rotating Machinery 10, n.º 6 (2004): 443–57. http://dx.doi.org/10.1155/s1023621x04000442.

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Gas turbines are used extensively for aircraft propulsion, land-based power generation, and industrial applications. Developments in turbine cooling technology play a critical role in increasing the thermal efficiency and power output of advanced gas turbines. Gas turbine blades are cooled internally by passing the coolant through several rib-enhanced serpentine passages to remove heat conducted from the outside surface. External cooling of turbine blades by film cooling is achieved by injecting relatively cooler air from the internal coolant passages out of the blade surface in order to form a protective layer between the blade surface and hot gas-path flow. For internal cooling, this presentation focuses on the effect of rotation on rotor blade coolant passage heat transfer with rib turbulators and impinging jets. The computational flow and heat transfer results are also presented and compared to experimental data using the RANS method with various turbulence models such as k-ε, and second-moment closure models. This presentation includes unsteady high free-stream turbulence effects on film cooling performance with a discussion of detailed heat transfer coef- ficient and film-cooling effectiveness distributions for standard and shaped film-hole geometry using the newly developed transient liquid crystal image method.

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6

Izmodenova, T. Yu, N. N. Kortikov y N. B. Kuznetsov. "Unsteady film cooling with imposed nonuniform pulsations of the main flow". Thermophysics and Aeromechanics 15, n.º 4 (diciembre de 2008): 583–88. http://dx.doi.org/10.1007/s11510-008-0007-1.

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7

Kim, Sung In y Ibrahim Hassan. "Unsteady Simulations of a Film Cooling Flow from an Inclined Cylindrical Jet". Journal of Thermophysics and Heat Transfer 24, n.º 1 (enero de 2010): 145–56. http://dx.doi.org/10.2514/1.33167.

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8

Muldoon, Frank. "Control of a Simplified Unsteady Film-Cooling Flow Using Gradient-Based Optimization". AIAA Journal 46, n.º 10 (octubre de 2008): 2443–58. http://dx.doi.org/10.2514/1.34120.

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9

Abhari, R. S. y A. H. Epstein. "An Experimental Study of Film Cooling in a Rotating Transonic Turbine". Journal of Turbomachinery 116, n.º 1 (1 de enero de 1994): 63–70. http://dx.doi.org/10.1115/1.2928279.

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Time-resolved measurements of heat transfer on a fully cooled transonic turbine stage have been taken in a short duration turbine test facility, which simulates full engine nondimensional conditions. The time average of this data is compared to uncooled rotor data and cooled linear cascade measurements made on the same profile. The film cooling reduces the time-averaged heat transfer compared to the uncooled rotor on the blade suction surface by as much as 60 percent, but has relatively little effect on the pressure surface. The suction surface rotor heat transfer is lower than that measured in the cascade. The results are similar over the central 3/4 of the span, implying that the flow here is mainly two dimensional. The film cooling is shown to be much less effective at high blowing ratios than at low ones. Time-resolved measurements reveal that the cooling, when effective, both reduced the dc level of heat transfer and changed the shape of the unsteady waveform. Unsteady blowing is shown to be a principal driver of film cooling fluctuations, and a linear model is shown to do a good job in predicting the unsteady heat transfer. The unsteadiness results in a 12 percent decrease in heat transfer on the suction surface and a 5 percent increase on the pressure surface.

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10

Yin, Hong. "Numerical simulation of swirling flow effect on the first stage vane film cooling distribution". International Journal of Modeling, Simulation, and Scientific Computing 07, n.º 03 (23 de agosto de 2016): 1650031. http://dx.doi.org/10.1142/s1793962316500318.

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In advanced gas turbine technology, lean premixed combustion is an effective strategy to reduce peak temperature and thus, NO[Formula: see text] emissions. The swirler is adopted to establish recirculation flow zone, enhancing mixing and stabilizing the flame. Therefore, the swirling flow is dominant in the combustor flow field and has impact on the vane. This paper mainly investigates the swirling flow effect on the turbine first stage vane cooling system by conducting a group of numerical simulations. Firstly, the numerical methods of turbulence modeling using RANS and LES are compared. The computational model of one single swirl flow field is considered. Both the RANS and LES results give reasonable recirculation zone shape. When comparing the velocity distribution, the RANS results generally match the experimental data but fail to at some local area. The LES modeling gives better results and more detailed unsteady flow field. In the second step, the RANS modeling is incorporated to investigate the vane film cooling performance under the swirling inflow boundary condition. According to the numerical results, the leading edge film cooling is largely altered by the swirling flow, especially for the swirl core-leading edge aligned case. Compared to the pressure side, the suction side film cooling is more sensitive to the swirling flow. Locally, the film cooling jet is lifted and turned by the strong swirling flow.

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11

Tyagi, Mayank y Sumanta Acharya. "Large Eddy Simulation of Film Cooling Flow From an Inclined Cylindrical Jet". Journal of Turbomachinery 125, n.º 4 (1 de octubre de 2003): 734–42. http://dx.doi.org/10.1115/1.1625397.

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Predictions of turbine blade film cooling have traditionally employed Reynolds-averaged Navier-Stokes solvers and two-equation models for turbulence. Evaluation of several versions of such models have revealed that the existing two-equation models fail to resolve the anisotropy and the dynamics of the highly complex flow field created by the jet-crossflow interaction. A more accurate prediction of the flow field can be obtained from large eddy simulations (LES) where the dynamics of the larger scales in the flow are directly resolved. In the present paper, such an approach has been used, and results are presented for a row of inclined cylindrical holes at blowing ratios of 0.5 and 1 and Reynolds numbers of 11,100 and 22,200, respectively, based on the jet velocity and hole diameter. Comparison of the time-averaged LES predictions with the flow measurements of Lavrich and Chiappetta (UTRC Report No. 90-04) shows that LES is able to predict the flow field with reasonable accuracy. The unsteady three-dimensional flow field is shown to be dominated by packets of hairpin-shaped vortices. The dynamics of the hairpin vortices in the wake region of the injected jet and their influence on the unsteady wall heat transfer are presented. Generation of “hot spots” and their migration on the film-cooled surface are associated with the entrainment induced by the hairpin structures. Several geometric properties of a “mixing interface” around hairpin coherent structures are presented to illustrate and quantify their impact on the entrainment rates and mixing processes in the wake region.

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12

Sarkar, S. "Flow structures and thermal field with modulated jet near the semi-circular leading edge". Proceedings of the Institution of Mechanical Engineers, Part A: Journal of Power and Energy 234, n.º 5 (7 de septiembre de 2019): 594–610. http://dx.doi.org/10.1177/0957650919873172.

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Influence of external modulation on unsteady flow and heat transfer near the leading edge of a constant thickness aerofoil has been described through large eddy simulation. This is a simplified approach to study film cooling activities near the leading edge of a turbine blade. Discrete jets, which are forced at a Strouhal number (St) of 0.37 with an averaged blowing ratio of unity, are ejected normally from a series of film cooling holes to a separated boundary layer. The results are compared against the corresponding steady injection. Larger coherent structures appear for a forced jet with an augmented vortex dynamics resulting in high jet lift-off, earlier break down, enhanced mixing with the cross flow and dilution of coolant layer. Resolved hairpins, which are the signature of coherent structures, illustrate that the vorticity and thermal field are highly correlated. Furthermore, evolution of hairpins and their advection control scalar transport and mixing. In brief, the modulation of coolant jet near the leading edge appears not beneficial for the combination of blowing ratio and frequency considered here.

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13

Rouina, S., M. Miranda y G. Barigozzi. "Experimental Investigation of the Unsteady Flow Behavior on a Film Cooling Flat Plate". Energy Procedia 101 (noviembre de 2016): 726–33. http://dx.doi.org/10.1016/j.egypro.2016.11.092.

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14

Abdullah, Kamil, Osama H. Abdulguad, Akmal Nizam Mohammed y Zaid Suleiman. "Comparison of RANS and U-RANS for Flat Plate Film Cooling". Applied Mechanics and Materials 773-774 (julio de 2015): 353–57. http://dx.doi.org/10.4028/www.scientific.net/amm.773-774.353.

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Film cooling has been extensively used to provide thermal protection for the external surfaces of gas turbine components. For the past 40 years, numerous number of film cooling hole designs and arrangements have been introduced. Due to broad designs and arrangements of film cooling, numerical investigation has been utilized to provide initial insight on the aerodynamics and thermal performance of the new film cooling designs or arrangements. The present work focuses on the numerical investigation of RANS and URANS analyses on a flat plate film cooling. The investigation aims to provide comparison between various turbulent models available for the Reynolds Average Navier Stokes (RANS) analyses and extended to unsteady Reynolds Average Navier Stokes (URANS). The numerical investigations make used of ANSYS CFX ver. 14 and were carried out at Reynolds Number, Re = 7,000 based on the hole diameter at blowing ratio, BR = 0.5. The results of the RANS analyses show significant influence of the turbulent models on the predicted aerodynamics and thermal performance of the film cooling. The result of URANS indicates limitation of RANS analyses to provide details on the eddied and vortices formation in film cooling flow structure.

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15

Gottlieb, Joshua, Roger Davis y John Clark. "Conjugate rotor-stator interaction procedure for film-cooled turbine sections". Aircraft Engineering and Aerospace Technology 89, n.º 3 (2 de mayo de 2017): 365–74. http://dx.doi.org/10.1108/aeat-10-2014-0159.

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Purpose The authors aim to present a procedure for the parallel, steady and unsteady conjugate, Navier–Stokes/heat-conduction rotor-stator interaction analysis of multi-blade-row, film-cooled, turbine airfoil sections. A new grid generation procedure for multiple blade-row configurations, including walls, thermal barrier coatings, plenums, and cooling tubes, is discussed. Design/methodology/approach Steady, multi-blade-row interaction effects on the flow and wall thermal fields are predicted using a Reynolds’s-averaged Navier–Stokes (RANS) simulation in conjunction with an inter-blade-row mixing plane. Unsteady, aero-thermal interaction solutions are determined using time-accurate sliding grids between the stator and rotor with an unsteady RANS model. Non-reflecting boundary condition treatments are utilized in both steady and unsteady approaches at all inlet, exit and inter-blade-row boundaries. Parallelization techniques are also discussed. Findings The procedures developed in this research are compared against experimental data from the Air Force Research Laboratory’s turbine research facility. Practical implications The software presented in this paper is useful as both the design and analysis tool for fluid system and turbomachinery engineers. Originality/value This research presents a novel approach for the simultaneous solution of fluid flow and heat transfer in film-cooled rotating turbine sections. The software developed in this research is validated against experimental results for 2D flow, and the methods discussed are extendable to 3D.

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16

Colban, W. F., A. T. Lethander, K. A. Thole y G. Zess. "Combustor Turbine Interface Studies—Part 2: Flow and Thermal Field Measurements". Journal of Turbomachinery 125, n.º 2 (1 de abril de 2003): 203–9. http://dx.doi.org/10.1115/1.1561812.

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Most turbine inlet flows resulting from the combustor exit are nonuniform in the near-platform region as a result of cooling methods used for the combustor liner. These cooling methods include injection through film-cooling holes and injection through a slot that connects the combustor and turbine. This paper presents thermal and flow field measurements in the turbine vane passage for a combustor exit flow representative of what occurs in a gas turbine engine. The experiments were performed in a large-scale wind tunnel facility that incorporates combustor and turbine vane models. The measured results for the thermal and flow fields indicate a secondary flow pattern in the vane passage that can be explained by the total pressure profile exiting the combustor. This secondary flow field is quite different than that presented for past studies with an approaching flat plate turbulent boundary layer along the upstream platform. A counter-rotating vortex that is positioned above the passage vortex was identified from the measurements. Highly turbulent and highly unsteady flow velocities occur at flow impingement locations along the stagnation line.

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17

Zhou, Wenwu, Han Chen, Yingzheng Liu, Xin Wen y Di Peng. "Unsteady analysis of adiabatic film cooling effectiveness for discrete hole with oscillating mainstream flow". Physics of Fluids 30, n.º 12 (diciembre de 2018): 127103. http://dx.doi.org/10.1063/1.5055028.

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18

Yuan, He-Peng, Hui-Ren Zhu, Man-Zhao Kong y Hai-Yong Liu. "Unsteady numerical investigation of back-step three-dimensional slots on film cooling effectiveness". Heat Transfer-Asian Research 38, n.º 1 (enero de 2009): 15–24. http://dx.doi.org/10.1002/htj.20236.

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19

Rasheed, Haroon, Zeeshan Khan, Ilyas Khan, Dennis Ching y Kottakkaran Nisar. "Numerical and Analytical Investigation of an Unsteady Thin Film Nanofluid Flow over an Angular Surface". Processes 7, n.º 8 (1 de agosto de 2019): 486. http://dx.doi.org/10.3390/pr7080486.

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In the present study, we examine three-dimensional thin film flow over an angular rotating disk plane in the presence of nanoparticles. The governing basic equations are transformed into ordinary differential equations by using similarity variables. The series solution has been obtained by the homotopy asymptotic method (HAM) for axial velocity, radial velocity, darning flow, induced flow, and temperature and concentration profiles. For the sake of accuracy, the results are also clarified numerically with the help of the BVPh2- midpoint method. The effect of embedded parameters such as the Brownian motion parameter Nb, Schmidt number Sc, thermophoretic parameter and Prandtl number Pr are explored on velocity, temperature and concentration profiles. It is observed that with the increase in the unsteadiness factor S, the thickness of the momentum boundary layer increases, while the Sherwood number Sc, with the association of heat flow from sheet to fluid, reduces with the rise in S and results in a cooling effect. It is also remarkable to note that the thermal boundary layer increases with the increase of the Brownian motion parameter Nb and Prandtl number Pr, hindering the cooling process resulting from heat transfer.

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20

Lee, S. L., Z. H. Yang y Y. Hsyua. "Cooling of a Heated Surface by Mist Flow". Journal of Heat Transfer 116, n.º 1 (1 de febrero de 1994): 167–72. http://dx.doi.org/10.1115/1.2910851.

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Cooling requirements in modern industrial applications, such as the removal of heat from electronic equipments, often demand the simultaneous attainment of a high heat flux and a low and relatively uniform and steady temperature of the heated surface to be cooled. The conventional single-phase convection cooling obviously cannot be expected to function adequately, since the heat flux there is directly proportional to the temperature difference between the heated surface and the surrounding medium. To maintain a high heat flux, the temperature of the heated surface usually must be kept at a high level. An attractive alternative is cooling by a spray, which takes advantage of the significant latent heat of evaporation of the liquid. However, in conventional industrial spray coolings, such as in the case of the cooling tower of a power plant, the temperature of the heated surface usually remains relatively high and is nonuniform and unsteady containing numerous flashy hot spots. In order to optimize the performance of the spray cooling of a heated surface by a mist flow, a clear understanding is required of (1) the dynamic interaction between the droplets and the carrier fluid and (2) the thermal reception of the droplets at the heated surface. It is the dynamic interaction between the phases that is causing the droplets to deposit onto the heated surface. The thermal reception at the heated wall develops mass and heat transfer leading to the mode of cooling of the heated surface. In the present study, an experimental investigation was made of the combination of the dynamic depositional behavior of droplets in a water droplet-air mist flow with the use of a specially designed particle-sizing two-dimensional laser-Doppler anemometer. Also, the heat transfer characteristics at the heated surface were investigated in relation to droplet deposition on the heated surface for wide ranges of droplet size, droplet concentration, mist flow velocity, and heat flux. It was discovered that over a certain suitable range of combination of these parameters, a superbly effective cooling scheme could be established by the evaporation on the outside surface of an ultrathin liquid film. Such a film was formed on the heated surface by the continuous deposition of fine droplets from the mist flow. Under these conditions, the heat flux is primarily related to the evaporation of the ultrathin liquid film on the heated surface and thus depends less on the temperature difference between the heated surf ace and the ambient mist flow. The heated surface is quenched to a low, relatively uniform and steady temperature at a very high level of heat flux. Heat transfer enhancement as high as seven times has been found so far. This effective heat transfer scheme is here termed mist cooling.

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21

Gao, Yan, Xin Yan, Jun Li y Kun He. "Investigations into film cooling and unsteady flow characteristics in a blade trailing-edge cutback region". Journal of Mechanical Science and Technology 32, n.º 10 (octubre de 2018): 5015–29. http://dx.doi.org/10.1007/s12206-018-0949-3.

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22

Zhou, Wenwu, Di Peng, Xin Wen, Yingzheng Liu y Hui Hu. "Unsteady analysis of adiabatic film cooling effectiveness behind circular, shaped, and sand-dune–inspired film cooling holes: Measurement using fast-response pressure-sensitive paint". International Journal of Heat and Mass Transfer 125 (octubre de 2018): 1003–16. http://dx.doi.org/10.1016/j.ijheatmasstransfer.2018.04.126.

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23

Shangguan, Yanqin, Xian Wang, Hu Zhang y Yueming Li. "LBM study on unsteady flow and heat-transfer behaviors of double-row film cooling with various row spacings". International Journal of Heat and Mass Transfer 138 (agosto de 2019): 1251–63. http://dx.doi.org/10.1016/j.ijheatmasstransfer.2019.04.115.

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24

Zamiri, Ali, Sung Jin You y Jin Taek Chung. "Large eddy simulation of unsteady turbulent flow structures and film-cooling effectiveness in a laidback fan-shaped hole". Aerospace Science and Technology 100 (mayo de 2020): 105793. http://dx.doi.org/10.1016/j.ast.2020.105793.

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25

Mirhosseini, Mojtaba, Alireza Rezania, Bo Iversen y Lasse Rosendahl. "Energy Harvesting from a Thermoelectric Zinc Antimonide Thin Film under Steady and Unsteady Operating Conditions". Materials 11, n.º 12 (24 de noviembre de 2018): 2365. http://dx.doi.org/10.3390/ma11122365.

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In practice, there are some considerations to study stability, reliability, and output power optimization of a thermoelectric thin film operating dynamically. In this study stability and performance of a zinc antimonide thin film thermoelectric (TE) specimen is evaluated under transient with thermal and electrical load conditions. Thermoelectric behavior of the specimen and captured energy in each part of a thermal cycle are investigated. Glass is used as the substrate of the thin film, where the heat flow is parallel to the length of the thermoelectric element. In this work, the thermoelectric specimen is fixed between a heat sink exposed to the ambient temperature and a heater block. The specimen is tested under various electrical load cycles during a wide range of thermal cycles. The thermal cycles are provided for five different aimed temperatures at the hot junction, from 160 to 350 °C. The results show that the specimen generates approximately 30% of its total electrical energy during the cooling stage and 70% during the heating stage. The thin film generates maximum power of 8.78, 15.73, 27.81, 42.13, and 60.74 kW per unit volume of the thermoelectric material (kW/m3), excluding the substrate, corresponding to hot side temperature of 160, 200, 250, 300, and 350 °C, respectively. Furthermore, the results indicate that the thin film has high reliability after about one thousand thermal and electrical cycles, whereas there is no performance degradation.

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26

Khan, Noor Saeed y Samina Zuhra. "Boundary layer flow and heat transfer in a thin-film second-grade nanoliquid embedded with graphene nanoparticles". Advances in Mechanical Engineering 11, n.º 11 (noviembre de 2019): 168781401988442. http://dx.doi.org/10.1177/1687814019884428.

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The two-dimensional magnetohydrodynamic unsteady movement and transmission of energy confined to finite domain layer of the second-grade nanofluid embedded with graphene nanoparticles on an expanding space are studied. Graphene nanoparticles have continuous electrical conductivity because the charge carrier movement in graphene bears extremely peak points compared to the available nanomaterials. The well-known system of equations for movement and energy of the second-grade nanofluid film accompanying the additional information have been transformed into the fourth-order coupled differential systems accompanying the auxiliary facts on behalf of simplifying substitutions. The simplified systems are evaluated via an efficient approach through homotopy analysis method which provides very clear relations for the motion and energy representatives. All the potential factors of the output are debated and portrayed pictorially. The results are useful in the analysis, design of coating, and cooling/heating processes.

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27

Hao, Z., X. Yang y Z. Feng. "Unsteady simulations of migration and deposition of fly-ash particles in the first-stage turbine of an aero-engine". Aeronautical Journal 125, n.º 1291 (12 de abril de 2021): 1566–86. http://dx.doi.org/10.1017/aer.2021.27.

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AbstractParticulate deposits in aero-engine turbines change the profile of blades, increase the blade surface roughness and block internal cooling channels and film cooling holes, which generally leads to the degradation of aerodynamic and cooling performance. To reveal particle deposition effects in the turbine, unsteady simulations were performed by investigating the migration patterns and deposition characteristics of the particle contaminant in a one-stage, high-pressure turbine of an aero-engine. Two typical operating conditions of the aero-engine, i.e. high-temperature take-off and economic cruise, were discussed, and the effects of particle size on the migration and deposition of fly-ash particles were demonstrated. A critical velocity model was applied to predict particle deposition. Comparisons between the stator and rotor were made by presenting the concentration and trajectory of the particles and the resulting deposition patterns on the aerofoil surfaces. Results show that the migration and deposition of the particles in the stator passage is dominated by the flow characteristics of fluid and the property of particles. In the subsequential rotor passage, in addition to these factors, particles are also affected by the stator–rotor interaction and the interference between rotors. With higher inlet temperature and larger diameter of the particle, the quantity of deposits increases and the deposition is distributed mainly on the Pressure Side (PS) and the Leading Edge (LE) of the aerofoil.

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28

Mehendale, A. B., J. C. Han, S. Ou y C. P. Lee. "Unsteady Wake Over a Linear Turbine Blade Cascade With Air and CO2 Film Injection: Part II—Effect on Film Effectiveness and Heat Transfer Distributions". Journal of Turbomachinery 116, n.º 4 (1 de octubre de 1994): 730–37. http://dx.doi.org/10.1115/1.2929466.

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The effect of unsteady wake flow and air (D.R. = 0.97) or CO2 (D.R. = 1.48) film injection on blade film effectiveness and heat transfer distributions was experimentally determined. A spoked wheel type wake generator produced the unsteady wake. Experiments were performed on a five-airfoil linear cascade in a low-speed wind tunnel at the chord Reynolds number of 3 × 105 for the no wake case and at the wake Strouhal numbers of 0.1 and 0.3. A model turbine blade with several rows of film holes on its leading edge, and pressure and suction surfaces ( −0.2<X/C< 0.4) was used. Results show that the blowing ratios of 1.2 and 0.8 provide the best film effectiveness over most of the blade surface for CO2 and air injections, respectively. An increase in the wake Strouhal number causes a decrease in film effectiveness over most of the blade surface for both density ratio injectants and at all blowing ratios. On the pressure surface, CO2 injection provides higher film effectiveness than air injection at the blowing ratio of 1.2; however, this trend is reversed at the blowing ratio of 0.8. On the suction surface, CO2 injection provides higher film effectiveness than air injection at the blowing ratio of 1.2; however, this trend is reversed at the blowing ratio of 0.4. Co2 injection provides lower heat loads than air injection at the blowing ratio of 1.2; however, this trend is reversed at the blowing ratio of 0.4. Heat load ratios under unsteady wake conditions are lower than the no wake case. For an actual gas turbine blade, since the blowing ratios can be greater than 1.2 and the density ratios can be up to 2.0, a higher density ratio coolant may provide lower heat load ratios under unsteady wake conditions.

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29

Zhou, Yu, Yuan Huang y Zhongqiang Mu. "Large eddy simulation of the influence of synthetic inlet turbulence on a practical aeroengine combustor with counter-rotating swirler". Proceedings of the Institution of Mechanical Engineers, Part G: Journal of Aerospace Engineering 233, n.º 3 (25 de diciembre de 2017): 978–90. http://dx.doi.org/10.1177/0954410017745900.

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To study the influence of inlet turbulence on the prediction of flow structure in practical aeroengine combustor, large eddy simulation with dynamic Smagorinsky subgrid model is used to explore the complex unsteady flow field in a single burner of a typical aeroengine combustor with two-stage counter-rotating swirler. The complex geometric configuration including all film cooling holes is fully simulated without any conventional simplification in order to reduce the modeling errors. First, unsteady process that flow developing from static to statistically stationary state is fully simulated under laminar inlet condition to obtain a fundamental understanding of flow characteristics in the combustor. Afterwards, synthetic eddy method is utilized to generate a turbulent inlet condition so that a perturbation with about 5% turbulence intensity is superimposed to the inlet plane. Simulation result shows that for the laminar inflow case, flow separation occurs in the near-wall region of the diffusion section, inducing a boundary layer transition and consequently introducing turbulence with nonuniformity in space before the swirler. In contrast, synthesized inflow generated under turbulent inlet condition by synthetic eddy method is more spatially homogeneous. Time-averaged flow field inside the swirler cup reveals that turbulent inflow ultimately causes the swirling flow with higher rotating speed in central region and more uniform distribution along the circumferential direction. It also enhances the transverse jet flow from primary holes and reverse flow in the central recirculation zone, and makes streamlines corresponding to the recirculation vortices more symmetrical on central profile. Maximum recirculating velocity predicted in central recirculation zone is −27.65 m/s and −17.86 m/s in turbulent and laminar case respectively, and corresponding total pressure recovery coefficient is 96.03% and 96.81%.

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30

Bons, J. P. y J. L. Kerrebrock. "1998 Heat Transfer Committee Best Paper Award: Complementary Velocity and Heat Transfer Measurements in a Rotating Cooling Passage With Smooth Walls". Journal of Turbomachinery 121, n.º 4 (1 de octubre de 1999): 651–62. http://dx.doi.org/10.1115/1.2836717.

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An experimental investigation was conducted on the internal flowfield of a simulated smooth-wall turbine blade cooling passage. The square cross-sectioned passage was manufactured from quartz for optical accessibility. Velocity measurements were taken using Particle Image Velocimetry for both heated and non-heated cases. Thin film resistive heaters on all four exterior walls of the passage allowed heat to be added to the coolant flow without obstructing laser access. Under the same conditions, an infrared detector with associated optics collected wall temperature data for use in calculating local Nusselt number. The test section was operated with radial outward flow and at values of Reynolds number and Rotation number typical of a small turbine blade. The density ratio was 0.27. Velocity data for the non-heated case document the evolution of the Coriolis-induced double vortex. The vortex has the effect of disproportionately increasing the leading side boundary layer thickness. Also, the streamwise component of the Coriolis acceleration creates a considerably thinned side wall boundary layer. Additionally, these data reveal a highly unsteady, turbulent flowfield in the cooling passage. Velocity data for the heated case show a strongly distorted streamwise profile indicative of a buoyancy effect on the leading side. The Coriolis vortex is the mechanism for the accumulation of stagnant flow on the leading side of the passage. Heat transfer data show a maximum factor of two difference in the Nusselt number from trailing side to leading side. A first-order estimate of this heat transfer disparity based on the measured boundary layer edge velocity yields approximately the same factor of two. A momentum integral model was developed for data interpretation, which accounts for coriolis and buoyancy effects. Calculated streamwise profiles and secondary flows match the experimental data well. The model, the velocity data, and the heat transfer data combine to strongly suggest the presence of separated flow on the leading wall starting at about five hydraulic diameters from the channel inlet for the conditions studied.

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31

Pyykkönen, J. M., David C. Martin, Mahesh C. Somani y P. T. Mäntylä. "Thermal Behaviour of Steel Plate during Accelerated Cooling". Materials Science Forum 638-642 (enero de 2010): 2706–11. http://dx.doi.org/10.4028/www.scientific.net/msf.638-642.2706.

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Recent trends in the production of high strength steel plate call for increasingly sophisticated thermo-mechanical treatment schedules, including the use of high rate accelerated cooling after finish rolling in order to achieve the desired microstructure and mechanical properties. Achieving the necessary cooling process control accuracy in such cases requires a sound understanding and description of the interactions between external heat transfer processes and changes in internal energy due to phenomena such as solid-state phase transformations. The thermal physical properties of the evolving microstructures of complex phase and martensitic steels vary greatly, and are strongly dependent on temperature and constituent phases. As a result, critical parameters such as thermal diffusivity cannot be accurately estimated without appropriate linkage to both phase transformation kinetics and temperature. In the present study, a numerical simulation has been developed to investigate the unsteady heat transfer and phase transformation behaviour of a moving steel plate during accelerated cooling. The simulation includes semi-empirical microstructure evolution sub-models, fitted to measured CCT data using non-linear regression. These are coupled to thermal-physical properties sub-models and thermal conduction calculations. A comprehensive suite of thermal boundary condition models which account for direct water cooling, forced convection film boiling, air cooling, radiation and heat transfer between plate and transport rollers are also included. The required equations for the plate temperature and microstructure evolution are solved numerically using a cell centred finite volume method, and the model has been validated by comparing simulated cooling stop temperatures with measurements obtained on the plate cooling section of an industrial plate mill. The predicted cooling stop temperatures of steel plates for different thicknesses, velocities and water flow rates are in good agreement with plant operational data.

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32

Jansson, L. S., L. Davidson y E. Olsson. "CALCULATION OF STEADY AND UNSTEADY FLOWS IN A FILM-COOLING ARRANGEMENT USING A TWO-LAYER ALGEBRAIC STRESS MODEL". Numerical Heat Transfer, Part A: Applications 25, n.º 3 (marzo de 1994): 237–58. http://dx.doi.org/10.1080/10407789408955947.

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33

Garg, Vijay K. "Heat Transfer on a Film-Cooled Rotating Blade Using a Two-Equation Turbulence Model". International Journal of Rotating Machinery 4, n.º 3 (1998): 201–16. http://dx.doi.org/10.1155/s1023621x98000177.

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A three-dimensional Navier–Stokes code has been used to compare the heat transfer coefficient on a film-cooled, rotating turbine blade. The blade chosen is the ACE rotor with five rows containing 93 film cooling holes covering the entire span. This is the only filmcooled rotating blade over which experimental data is available for comparison. Over 2.278 million grid points are used to compute the flow over the blade including the tip clearance region, using Coakley'sq-ωturbulence model. Results are also compared with those obtained by Garg and Abhari (1997) using the zero-equation Baldwin-Lomax (B-L) model. A reasonably good comparison with the experimental data is obtained on the suction surface for both the turbulence models. At the leading edge, the B-L model yields a better comparison than theq-ωmodel. On the pressure surface, however, the comparison between the experimental data and the prediction from either turbulence model is poor. A potential reason for the discrepancy on the pressure surface could be the presence of unsteady effects due to stator-rotor interaction in the experiments which are not modeled in the present computations. Prediction using the two-equation model is in general poorer than that using the zero-equation model, while the former requires at least 40% more computational resources.

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34

Cai, Tao, Di Peng, Savas Yavuzkurt y Ying Zheng Liu. "Unsteady 2-D film-cooling effectiveness behind a single row of holes at different blowing ratios: Measurements using fast-response pressure-sensitive paint". International Journal of Heat and Mass Transfer 120 (mayo de 2018): 1325–40. http://dx.doi.org/10.1016/j.ijheatmasstransfer.2017.12.141.

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35

Chen, Da-wei, Hui-ren Zhu, Cun-liang Liu, Hua-tai Li, Bing-ran Li y Dao-en Zhou. "Combined effects of unsteady wake and free-stream turbulence on turbine blade film cooling with laid-back fan-shaped holes using PSP technique". International Journal of Heat and Mass Transfer 133 (abril de 2019): 382–92. http://dx.doi.org/10.1016/j.ijheatmasstransfer.2018.12.102.

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36

Dunn, Michael G. "Convective Heat Transfer and Aerodynamics in Axial Flow Turbines". Journal of Turbomachinery 123, n.º 4 (1 de febrero de 2001): 637–86. http://dx.doi.org/10.1115/1.1397776.

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The primary focus of this paper is convective heat transfer in axial flow turbines. Research activity involving heat transfer generally separates into two related areas: predictions and measurements. The problems associated with predicting heat transfer are coupled with turbine aerodynamics because proper prediction of vane and blade surface-pressure distribution is essential for predicting the corresponding heat transfer distribution. The experimental community has advanced to the point where time-averaged and time-resolved three-dimensional heat transfer data for the vanes and blades are obtained routinely by those operating full-stage rotating turbines. However, there are relatively few CFD codes capable of generating three-dimensional predictions of the heat transfer distribution, and where these codes have been applied the results suggest that additional work is required. This paper outlines the progression of work done by the heat transfer community over the last several decades as both the measurements and the predictions have improved to current levels. To frame the problem properly, the paper reviews the influence of turbine aerodynamics on heat transfer predictions. This includes a discussion of time-resolved surface-pressure measurements with predictions and the data involved in forcing function measurements. The ability of existing two-dimensional and three-dimensional Navier–Stokes codes to predict the proper trends of the time-averaged and unsteady pressure field for full-stage rotating turbines is demonstrated. Most of the codes do a reasonably good job of predicting the surface-pressure data at vane and blade midspan, but not as well near the hub or the tip region for the blade. In addition, the ability of the codes to predict surface-pressure distribution is significantly better than the corresponding heat transfer distributions. Heat transfer codes are validated against measurements of one type or another. Sometimes the measurements are performed using full rotating rigs, and other times a much simpler geometry is used. In either case, it is important to review the measurement techniques currently used. Heat transfer predictions for engine turbines are very difficult because the boundary conditions are not well known. The conditions at the exit of the combustor are generally not well known and a section of this paper discusses that problem. The majority of the discussion is devoted to external heat transfer with and without cooling, turbulence effects, and internal cooling. As the design community increases the thrust-to-weight ratio and the turbine inlet temperature, there remain many turbine-related heat transfer issues. Included are film cooling modeling, definition of combustor exit conditions, understanding of blade tip distress, definition of hot streak migration, component fatigue, loss mechanisms in the low turbine, and many others. Several suggestions are given herein for research and development areas for which there is potentially high payoff to the industry with relatively small risk.

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37

Кухтин, Юрий Петрович y Руслан Юрьевич Шакало. "СНИЖЕНИЕ ВИБРОНАПРЯЖЕННОСТИ ПОПАРНО БАНДАЖИРОВАННЫХ РАБОЧИХ ЛОПАТОК ТУРБИНЫ". Aerospace technic and technology, n.º 7 (31 de agosto de 2020): 52–58. http://dx.doi.org/10.32620/aktt.2020.7.08.

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To reduce the vibration stresses arising in the working blades of turbines during resonant excitations caused by the frequency of passage of the blades of the nozzle apparatus, it is necessary to control the level of aerodynamic exciting forces. One of the ways to reduce dynamic stresses in rotor blades under operating conditions close to resonant, in addition to structural damping, maybe to reduce external exciting forces. To weaken the intensity of the exciting forces, it is possible to use a nozzle apparatus with multi-step gratings, as well as with non-radially mounted blades of the nozzle apparatus.This article presents the results of numerical calculations of exciting aerodynamic forces, as well as the results of experimental measurements of stresses arising in pairwise bandaged working blades with a frequency zCA ⋅ fn, where fn – is the rotor speed, zCA – is the number of nozzle blades. The object of research was the high-pressure turbine stage of a gas turbine engine. Two variants of a turbine stage were investigated: with the initial geometry of the nozzle apparatus having the same geometric neck area in each interscapular channel and with the geometry of the nozzle apparatus obtained by alternating two types of sectors with a reduced and initial throat area.The presented results are obtained on the basis of numerical simulation of a viscous unsteady gas flow in a transonic turbine stage using the SUnFlow home code, which implements a numerical solution of the Reynolds-averaged Navier-Stokes equations. Discontinuity of a torrent running on rotor blades is aggravated with heat drops between an ardent flow core and cold jets from film cooling of a blade and escapes on clock surfaces. Therefore, at simulation have been allowed all blowngs cooling air and drain on junctions of shelves the impeller.As a result of the replacement of the nozzle apparatus with a constant passage area by a nozzle apparatus with a variable area, a decrease in aerodynamic driving force by 12.5 % was obtained. The experimentally measured stresses arising in a pairwise bandaged blade under the action of this force decreased on average by 26 %.

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38

Li, Shuai, Zongjing Yuan y Gang Chen. "Numerical investigation of unsteady mixing mechanism in plate film cooling". Theoretical and Applied Mechanics Letters 6, n.º 5 (septiembre de 2016): 213–21. http://dx.doi.org/10.1016/j.taml.2016.08.007.

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39

TANAKA, Yudai, Yutaka ODA y Yuki YONEDA. "Unsteady Measurement of Film Cooling Effectiveness Using Fast-Response PSP". Proceedings of Conference of Kansai Branch 2019.94 (2019): P039. http://dx.doi.org/10.1299/jsmekansai.2019.94.p039.

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40

Medic, G. y P. A. Durbin. "Unsteady Effects on Trailing Edge Cooling". Journal of Heat Transfer 127, n.º 4 (30 de marzo de 2005): 388–92. http://dx.doi.org/10.1115/1.1860565.

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It is shown how natural and forced unsteadiness play a major role in turbine blade trailing edge cooling flows. Reynolds averaged simulations are presented for a surface jet in coflow, resembling the geometry of the pressure side breakout on a turbine blade. Steady computations show very effective cooling; however, when natural—or even moreso, forced—unsteadiness is allowed, the adiabatic effectiveness decreases substantially. Streamwise vortices in the mean flow are found to be the cause of the increased heat transfer.

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41

Du, H., S. V. Ekkad y J. C. Han. "Effect of Unsteady Wake With Trailing Edge Coolant Ejection on Film Cooling Performance for a Gas Turbine Blade". Journal of Turbomachinery 121, n.º 3 (1 de julio de 1999): 448–55. http://dx.doi.org/10.1115/1.2841337.

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The effect of unsteady wakes with trailing edge coolant ejection on surface heat transfer coefficients and film cooling effectiveness is presented for a downstream film-cooled turbine blade. The detailed heat transfer coefficient and film effectiveness distributions on the blade surface are obtained using a transient liquid crystal technique. Unsteady wakes are produced by a spoked wheel-type wake generator upstream of the five-blade linear cascade. The coolant jet ejection is simulated by ejecting coolant through holes on the hollow spokes of the wake generator. For a blade without film holes, unsteady wake increases both pressure side and suction side heat transfer levels due to early boundary layer transition. Adding trailing edge ejection to the unsteady wake further enhances the blade surface heat transfer coefficients particularly near the leading edge region. For a film-cooled blade, unsteady wake effects slightly enhance surface heat transfer coefficients but significantly reduces film effectiveness. Addition of trailing edge ejection to the unsteady wake has a small effect on surface heat transfer coefficients compared to other significant parameters such as film injection, unsteady wakes, and grid generated turbulence, in that order. Trailing edge ejection effect on film effectiveness distribution is stronger than on the heat transfer coefficients.

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42

Du, H., J. C. Han y S. V. Ekkad. "Effect of Unsteady Wake on Detailed Heat Transfer Coefficient and Film Effectiveness Distributions for a Gas Turbine Blade". Journal of Turbomachinery 120, n.º 4 (1 de octubre de 1998): 808–17. http://dx.doi.org/10.1115/1.2841793.

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Unsteady wake effects on detailed heat transfer coefficient and film cooling effectiveness distributions from a gas turbine blade with film cooling are obtained using a transient liquid crystal technique. Tests were performed on a five-blade linear cascade at a axial chord Reynolds number of 5.3 × 105 at cascade exit. Upstream unsteady wakes are simulated using a spoke-wheel type wake generator. The test blade has three rows of film holes on the leading edge and two rows each on the pressure and suction surfaces. Air and CO2 were used as coolants to simulate different coolant-to-mainstream density ratio effect. Coolant blowing ratio for air injection is varied from 0.8 to 1.2 and is varied from 0.4 to 1.2 for CO2. Results show that Nusselt numbers for a film-cooled blade are much higher compared to a blade without film injection. Particularly, film injection causes earlier boundary layer transition on the suction surface. Unsteady wakes slightly enhance Nusselt numbers but significantly reduce film cooling effectiveness on a film-cooled blade compared with a film-cooled blade without wakes. Nusselt numbers increase slightly but film cooling effectiveness increase significantly with an increase in blowing ratio for CO2 injection. Higher density coolant (CO2) provides higher effectiveness at higher blowing ratios (M = 1.2) whereas lower density coolant (Air) provides higher effectiveness at lower blowing ratios (M = 0.8).

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43

Miau, J. J., T. S. Leu, J. M. Yu, J. K. Tu, C. T. Wang, V. Lebiga, D. Mironov, A. Pak, V. Zinovyev y K. M. Chung. "Mems thermal film sensors for unsteady flow measurement". Sensors and Actuators A: Physical 235 (noviembre de 2015): 1–13. http://dx.doi.org/10.1016/j.sna.2015.09.030.

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44

Ligrani, P. M., R. Gong, J. M. Cuthrell y J. S. Lee. "Bulk flow pulsations and film cooling—II. Flow structure and film effectiveness". International Journal of Heat and Mass Transfer 39, n.º 11 (julio de 1996): 2283–92. http://dx.doi.org/10.1016/0017-9310(95)00287-1.

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45

MAO, YADAN, CHENGWANG LEI y JOHN C. PATTERSON. "Unsteady near-shore natural convection induced by surface cooling". Journal of Fluid Mechanics 642 (4 de diciembre de 2009): 213–33. http://dx.doi.org/10.1017/s0022112009991765.

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Natural convection in calm near-shore waters induced by daytime heating or nighttime cooling plays a significant role in cross-shore exchanges with significant biological and environmental implications. Having previously reported an improved scaling analysis on the daytime radiation-induced natural convection, the authors present in this paper a detailed scaling analysis quantifying the flow properties at varying offshore distances induced by nighttime surface cooling. Two critical functions of offshore distance have been derived to identify the distinctness and the stability of the thermal boundary layer. Two flow scenarios are possible depending on the bottom slope. For the relatively large slope scenario, three flow regimes are possible, which are discussed in detail. For each flow regime, all the possible distinctive subregions are identified. Two different sets of scaling incorporating the offshore-distance dependency have been derived for the conduction-dominated region and stable-convection-dominated region respectively. It is found that the scaling for flow in the stable-convection-dominated region also applies to the time-averaged mean flow in the unstable region. The present scaling results are verified by numerical simulations.

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46

Zhou, Li, Hong-zhou Fan, Xin Zhang y Yuan-hu Cai. "Investigation of Effect of Unsteady Interaction on Turbine Blade Film Cooling". Engineering Applications of Computational Fluid Mechanics 5, n.º 4 (enero de 2011): 487–98. http://dx.doi.org/10.1080/19942060.2011.11015388.

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47

Yi, Weilin, Lucheng Ji y Yunhan Xiao. "Unsteady numerical simulation of hot streak/blades interaction and film cooling". Journal of Thermal Science 19, n.º 5 (28 de agosto de 2010): 402–9. http://dx.doi.org/10.1007/s11630-010-0401-1.

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48

Fawcett, Richard J., Andrew P. S. Wheeler, Li He y Rupert Taylor. "Experimental Investigation Into Unsteady Effects on Film Cooling". Journal of Turbomachinery 134, n.º 2 (28 de junio de 2011). http://dx.doi.org/10.1115/1.4003053.

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The benefits of different film cooling geometries are typically assessed in terms of their time-averaged performance. It is known that the mixing between the coolant film and the main turbine passage flow is an unsteady process. The current study investigates the forms of unsteadiness that occur in engine-representative film cooling flows and how this unsteadiness affects the mixing with the mainstream flow. Cylindrical and fan-shaped cooling holes across a range of hole blowing ratios have been studied experimentally using particle image velocimetry and high speed photography. Coherent unsteadiness is found in the shear layer between the jet and the mainstream for both cylindrical and fan-shaped cooling holes. Its occurrence and sense of rotation is found to be controlled by the velocity difference between the mainstream flow and the jet, which is largely determined by the blowing ratio.

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49

Rutledge, James L., Paul I. King y Richard Rivir. "Time Averaged Net Heat Flux Reduction for Unsteady Film Cooling". Journal of Engineering for Gas Turbines and Power 132, n.º 12 (24 de agosto de 2010). http://dx.doi.org/10.1115/1.4001810.

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Film cooling flow for reduction in heat flux to a gas turbine engine hot gas path component is generally assumed to be steady. However, unsteady film cooling may occur due to naturally occurring flow unsteadiness or may be induced intentionally. Analysis of pulsed or otherwise unsteady film coolant flow necessitates a reformulation of the existing steady-state technique for net heat flux reduction (NHFR). We show that addition of a cross-coupled term to the traditional steady form of the NHFR equation with time averaged quantities accounts for the unsteady effects. In the experimental technique to determine the time averaged NHFR, we present a new parameter γ to capture the combined influence of the average adiabatic effectiveness and the coupling between η′ and h′. Measurement of γ is shown to be straightforward but requiring careful considerations beyond those required to measure η with steady film cooling.

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50

Bernsdorf, Stefan, Martin G. Rose y Reza S. Abhari. "Experimental Validation of Quasisteady Assumption in Modeling of Unsteady Film-Cooling". Journal of Turbomachinery 130, n.º 1 (1 de enero de 2008). http://dx.doi.org/10.1115/1.2720878.

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This paper reports on the validation of the assumption of quasisteady behavior of pulsating cooling injection in the near hole flow region. The respective experimental data are taken in a flat plate wind tunnel at ETH Zürich. The facility simulates the film cooling row flow field on the pressure side of a turbine blade. Engine representative nondimensionals are achieved, providing a faithful model at a larger scale. Heating the free stream air and strongly cooling the coolant gives the required density ratio between coolant and free-stream. The coolant is injected with different frequency and amplitude. The three-dimensional velocities are recorded using nonintrusive PIV, and seeding is provided for both air streams. Two different cylindrical hole geometries are studied, with different angles. Blowing ratio is varied over a range to simulate pressure side film cooling. The general flow field, the jet trajectory, and the streamwise circulation are utilized in the validation of the quasisteady assumption.

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