Academic literature on the topic 'Turbulence. Vortex-motion. Heat'
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Journal articles on the topic "Turbulence. Vortex-motion. Heat"
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Donnelly, Russell J., and Charles E. Swanson. "Quantum turbulence." Journal of Fluid Mechanics 173 (December 1986): 387–429. http://dx.doi.org/10.1017/s0022112086001210.
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We present a review of quantum turbulence, that is, the turbulent motion of quantized vortex lines in superfluid helium. Our discussion concentrates on the turbulence produced by steady, uniform heat flow in a pipe, but touches on other turbulent flows as well. We have attempted to motivate the study of quantum turbulence and discuss briefly its connection with classical turbulence. We include background on the two-fluid model and mutual friction theory, examples of modern experimental techniques, and a brief survey of the phenomenology. We discuss the important recent insights that vortex dynamics has provided to the understanding of quantum turbulence, from simple scaling arguments to detailed numerical simulations. We conclude with a discussion of open questions in this field.
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Akcayoglu, Azize, and Celal Nazli. "Thermal enhancement of triangular fins based on spanwise distance of vortex generators." Proceedings of the Institution of Mechanical Engineers, Part C: Journal of Mechanical Engineering Science 231, no. 13 (March 7, 2016): 2554–66. http://dx.doi.org/10.1177/0954406216636917.
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In this study, the influence of spanwise positions of vortex generators on the fin performance is determined numerically by considering global and local flow and heat transfer fields. The vortex generators are located on the inclined surfaces of equilateral triangular fins and the spanwise distances between them are altered as much as possible depending on the extents of the triangular duct. “RNG k-ɛ” turbulence model with “Enhanced wall treatment” option is determined as the best turbulence model to predict the flow fields inside the triangular fins with built-in vortex generators, for Reynolds number of 5000. It is found that the best performance is achieved when the spanwise distance between the common flow up and common flow down type vortex generator pairs and the triangular duct base are equal to 0.23 and 1.11 times the vortex generator length, respectively. The optimum spanwise distance between the vortex generators is determined as 0.88 times the vortex generator length. The determined values reinforced the secondary flow interactions including mixing of hot and cold fluids, generation of turbulence, swirling motion of vortices, and interaction of vortices with the main flow. The obtained results are useful in designing triangular heat exchangers with built-in delta-winglet type vortex generators.
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Kondaraju, S., and J. S. Lee. "Hybrid turbulence simulation of spray impingement cooling: The effect of vortex motion on turbulent heat flux." International Journal for Numerical Methods in Fluids 59, no. 6 (February 28, 2009): 657–76. http://dx.doi.org/10.1002/fld.1828.
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Yariz, V., V. Nikolsky, E. Gnatko, A. Palagnyuk, А. Lobodenko, V. Ved, and S. Pavlyus. "Study of the motion of incompressible gas in a vortex heat generator." Computer Modeling: Analysis, Control, Optimization 8, no. 2 (December 2020): 75–81. http://dx.doi.org/10.32434/2521-6406-2020-8-2-75-81.
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The article presents the results of the performed analytical and experimental studies of the hydrodynamics of the translationalrotational motion of a viscous incompressible gas flow in the working space of a vortex heat generator of variable geometry, analytically determined the dependences of the effect of device performance, confuser opening angles, confuser channel width on the hydrodynamic parameters of the device and, as a consequence, its energy efficiency. The degree of energy efficiency of the swirler screw for the operation of a vortex heat generator at various loads on the working path has been experimentally estimated, according to the Euler number EUc. It has been proven that the energy efficiency of its operation is on average 35% higher when the swirler screw is installed. The influence of the geometry of the nozzle on the axial symmetry and smoothness of the flow of incompressible gas in the vortex chamber is investigated. It was found that the specified indicator is most satisfactory for a nozzle with a rectangular cross-section. The distribution of the temperature field of a moving incompressible gas along the height of the vortex chamber is investigated depending on the taper angle. The distribution of angular velocities along the axis of the flow swirler is investigated at various values of productivity. It was found that the angular velocity decreases according to the law of potential fluid flow. A mathematical model has been developed to optimize the operating modes and parameters of the vortex heat generator. A software block was built based on the mathematical package MathCAD version 11 for the implementation of the developed mathematical model. An optimal design of a vortex heat generator with a variable geometry of the working space has been developed, which has been tested in laboratory conditions. Laboratory studies have proven its high energy efficiency at the level of modern standards and the feasibility of using the device for heating buildings and structures in industry and the domestic sector. Keywords: incompressible gas, hydrodynamics of an incompressible gas flow, vortex motion, mathematical model, equation of motion, continuity equation, vortex heat generator, thermal energy, cavitation, turbulence, vortex zone, MathCAD package.
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Wang, Ting, and Matthew C. Rice. "Effect of Elevated Free-Stream Turbulence on Transitional Flow Heat Transfer Over Dual-Scaled Rough Surfaces." Journal of Heat Transfer 127, no. 4 (March 30, 2005): 393–403. http://dx.doi.org/10.1115/1.1861920.
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The surface roughness over a serviced turbine airfoil is usually multiscaled with varying features that are difficult to be universally characterized. However, it was previously discovered in low free-stream turbulence conditions that the height of larger roughness produces separation and vortex shedding, which trigger early transition and exert a dominant effect on flow pattern and heat transfer. The geometry of the roughness and smaller roughness scales played secondary roles. This paper extends the previous study to elevated turbulence conditions with free-stream turbulence intensity ranging from 0.2% to 6.0%. A simplified test condition on a flat plate is conducted with two discrete regions having different surface roughness. The leading-edge roughness is comprised of a sandpaper strip or a single cylinder. The downstream surface is either smooth or covered with sandpaper of grit sizes ranging from 100 to 40 Ra=37-119 μm. Hot wire measurements are conducted in the boundary layer to study the flow structure. The results of this study verify that the height of the largest-scale roughness triggers an earlier transition even under elevated turbulence conditions and exerts a more dominant effect on flow and heat transfer than does the geometry of the roughness. Heat transfer enhancements of about 30–40%-over the entire test surface are observed. The vortical motion, generated by the backward facing step at the joint of two roughness regions, is believed to significantly increase momentum transport across the boundary layer and bring the elevated turbulence from the freestream towards the wall. No such long-lasting heat transfer phenomenon is observed in low free-stream turbulence cases even though vortex shedding also exists in the low turbulence cases. The heat transfer enhancement decreases, instead of increases, as the downstream roughness height increases.
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Aw Lin, Chou, Fatimah Al-Zahrah Mohd Sa’at, Fadhilah Shikh Anuar, Mohamad Firdaus Sukri, Mohd Zaid Akop, and Zainuddin Abdul Manan. "Heat Transfer Across Tube Banks With a Passive Control Vortex Generator in Steady One-Directional and Oscillatory Flows." CFD Letters 13, no. 1 (January 31, 2021): 1–18. http://dx.doi.org/10.37934/cfdl.13.1.118.
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Fluid can flow in one-directional (normal flow) or oscillatory conditions. Fluid flow in some energy system involved oscillatory flow condition. The use of vortex generator has been proven to improve heat transfer in the case of one-directional flow but the impact of vortex generator in oscillatory flow condition is yet unknown. This study focusses on the heat transfer performance across a heated tube banks using a Computational Fluid Dynamics (CFD) model. Two flow conditions were modelled: steady one-directional and oscillatory flow conditions. Two-dimensional CFD models of steady flow and oscillatory flow were solved using the SST k-? turbulence model for two different cases of heated tube banks with and without the vortex generators. The heat transfer performance for both flow conditions were analysed by considering a heat transfer parameter known as Colburn-j factor. Results showed that the use of a vortex generator increased the heat transfer enhancement, regardless of the flow conditions. However, it is also noted that the heat transfer behaviour in a steady flow and an oscillatory flow is not the same, especially with the appearance of secondary flows in the system. The difference is discussed with respect to dimensionless quantity of Colburn j-factor, the non-dimensionless quantity, and the amplitude of temperature field. The result indicates that the heat equation in the steady flow condition is not very suitable to be directly used in oscillatory flow conditions. Appropriate heat equation needs to be properly addressed for situations that involve oscillatory flow motion.
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Lin, W. L., and T. F. Lin. "Observation and Computation of Vortex and/or Reverse Flow Development in Mixed Convection of Air in a Slightly Inclined Rectangular Duct." Journal of Heat Transfer 119, no. 4 (November 1, 1997): 691–99. http://dx.doi.org/10.1115/1.2824173.
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Combined flow visualization and conjugated numerical heat transfer analysis were carried out to study the axial evolution of the buoyancy induced secondary vortex and reverse flow in a mixed convective air flow through a bottom heated, slightly inclined rectangular duct. Results were obtained for the Grashof number Gr ranging from 1.6 × 103 to 2.8 × 105, inclined angle φ from −20 deg to 26 deg and the Reynolds number Re below 102 covering the steady and time dependent flows. For the buoyancy-opposing case, at a certain critical buoyancy-to-inertia ratio depending on the Re and φ both the experimental and numerical results clearly showed the generation of the longitudinal vortex rolls in the entry half of the duct and a slender reverse flow zone was induced near the exit end of the duct. At a higher buoyancy-to-inertia ratio the stronger reverse flow moves upstream and is in a time periodic snaking motion which is considered to result from the Kelvin-Helmholtz instability associated with the two counter flow streams, namely, the downstream moving longitudinal vortex rolls and the upstream moving reverse flow. Through the viscous shearing effects the strong snaking reverse flow induces a number of eddies moving along it and the longitudinal rolls are pushed towards the duct sides. This strong interaction between the vortex flow and reverse flow leads to an earlier transition to turbulence. A correlation equation was proposed for the penetration length of the reverse flow. However, for buoyancy-assisting flow no reverse flow is induced and the longitudinal vortex rolls prevail for the buoyancy-to-inertia ratio up to 2.8 × 105. Significant conjugated heat transfer effects were noted from the numerical results.
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Antonia, R. A., L. W. B. Browne, D. K. Bisset, and L. Fulachier. "A description of the organized motion in the turbulent far wake of a cylinder at low Reynolds number." Journal of Fluid Mechanics 184 (November 1987): 423–44. http://dx.doi.org/10.1017/s0022112087002957.
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The topology of the organized motion has been obtained in the slightly heated self-preserving far wake of a circular cylinder at a Reynolds number, based on the cylinder diameter, of about 1200. In a frame of reference moving with the organized motion, the toplogy in the plane of main shear reduces to a succession of centres and saddles, located at about the wake half-width. Centres are identifiable by large values of spanwise vorticity associated with the coherent large-scale motion. Saddles occur at the intersection of converging and diverging separatrices, the latter being identifiable with the high strain rate due to the large-scale motion. Large values of the longitudinal turbulence intensity associated with the smaller-scale motion occur at the centres. High values of the normal and shear stresses, the temperature variance and heat fluxes associated with the large-scale motion occur on either side of each saddle point along the direction of the diverging separatrix. Contours for the production of energy and temperature variance associated with the small-scale motion are aligned along the diverging separatrices, and have maxima near the saddle point. Contours for one component of the dissipation of small-scale temperature variance also have a high concentration along the diverging separatrix. Flow visualizations in the far wake suggest the existence of groups of three-dimensional bulges which are made up of clusters of vortex loops.
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Kim, Youngwoo, Chanhee Moon, Omid Nematollahi, Hyun Dong Kim, and Kyung Chun Kim. "Time-Resolved PIV Measurements and Turbulence Characteristics of Flow Inside an Open-Cell Metal Foam." Materials 14, no. 13 (June 25, 2021): 3566. http://dx.doi.org/10.3390/ma14133566.
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Open-cell metal foams are porous medium for thermo-fluidic systems. However, their complex geometry makes it difficult to perform time-resolved (TR) measurements inside them. In this study, a TR particle image velocimetry (PIV) method is introduced for use inside open-cell metal foam structures. Stereolithography 3D printing methods and conventional post-processing methods cannot be applied to metal foam structures; therefore, PolyJet 3D printing and post-processing methods were employed to fabricate a transparent metal foam replica. The key to obtaining acceptable transparency in this method is the complete removal of the support material from the printing surfaces. The flow characteristics inside a 10-pore-per-inch (PPI) metal foam were analyzed in which porosity is 0.92 while laminar flow condition is applied to inlet. The flow inside the foam replica is randomly divided and combined by the interconnected pore network. Robust crosswise motion occurs inside foam with approximately 23% bulk speed. Strong influence on transverse motion by metal foam is evident. In addition, span-wise vorticity evolution is similar to the integral time length scale of the stream-wise center plane. The span-wise vorticity fluctuation through the foam arrangement is presented. It is believed that this turbulent characteristic is caused by the interaction of jets that have different flow directions inside the metal foam structure. The finite-time Lyapunov exponent method is employed to visualize the vortex ridges. Fluctuating attracting and repelling material lines are expected to enhance the heat and mass transfer. The results presented in this study could be useful for understanding the flow characteristics inside metal foams.
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Houze, Robert A., Wen-Chau Lee, and Michael M. Bell. "Convective Contribution to the Genesis of Hurricane Ophelia (2005)." Monthly Weather Review 137, no. 9 (September 1, 2009): 2778–800. http://dx.doi.org/10.1175/2009mwr2727.1.
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Abstract The convection occurring in the tropical depression that became Hurricane Ophelia (2005) was investigated just prior to tropical storm formation. Doppler radar showed a deep, wide, intense convective cell of a type that has been previously thought to occur in intensifying tropical depressions but has not heretofore been documented in detail. The updraft of the cell was 10 km wide, 17 km deep, had updrafts of 10–20 m s−1 throughout its mid- to upper levels, and contained a cyclonic vorticity maximum. The massive convective updraft was maintained by strong positive buoyancy, which was maximum at about the 10-km level, probably aided by latent heat of freezing. Evaporative cooling and precipitation drag occurred in the rain shower of the cell but were insufficient to produce a strong downdraft or gust front outflow to force the updraft. The convective updraft was fed by a layer of strong inflow that was several kilometers deep. Wind-induced turbulence, just above the ocean surface, enriched the equivalent potential temperature of the boundary layer of the inflow air, thus creating an unstable layer with little convective inhibition. This air was raised to its level of free convection when it encountered the denser air in the rainy core of the convection. The updraft motion and latent heat release in the intense cell generated potential vorticity throughout the low to midlevels, and contained a cyclonic vortex at the midlevels. Vorticity generated throughout the depth of the low to midtroposphere within convective updraft cells was subsequently incorporated into a stratiform region attached to the region of active convective cells. The vorticity perturbations at the low to midlevels in convective cells and their attached stratiform regions were available to be axisymmetrized into the larger-scale intensifying depression vortex.
Dissertations / Theses on the topic "Turbulence. Vortex-motion. Heat"
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Swisher, Stacey Elaine. "Time-resolved heat flux measurements of the turbulent junction vortex system." Thesis, This resource online, 1991. http://scholar.lib.vt.edu/theses/available/etd-10312009-020052/.
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Praisner, Thomas J. "Investigation of turbulent juncture flow endwall heat transfer and flow field /." Diss., 1998. http://gateway.proquest.com/openurl?url_ver=Z39.88-2004&rft_val_fmt=info:ofi/fmt:kev:mtx:dissertation&res_dat=xri:pqdiss&rft_dat=xri:pqdiss:9831809.
Full textBooks on the topic "Turbulence. Vortex-motion. Heat"
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1932-, Fiebig Martin, Mitra Nimai K, and Deutsche Forschungsgemeinschaft, eds. Vortices and heat transfer: Results of a DFG-supported research group. Braunschweig/Wiesbaden: Vieweg, 1998.
Find full textConference papers on the topic "Turbulence. Vortex-motion. Heat"
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Wang, Ting, and Matthew C. Rice. "Effect of Elevated Free-Stream Turbulence on Transitional Heat Transfer Over Dual-Scaled Rough Surfaces." In ASME Turbo Expo 2003, collocated with the 2003 International Joint Power Generation Conference. ASMEDC, 2003. http://dx.doi.org/10.1115/gt2003-38835.
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The surface roughness over a serviced turbine airfoil is usually multi-scaled with varying features that are difficult to be universally characterized. However, it was previously discovered in low freestream turbulence conditions that the height of larger roughness produces separation and vortex shedding, which trigger early transition and exert a dominant effect on flow pattern and heat transfer. The geometry of the roughness and smaller roughness scales played secondary roles. This paper extends the previous study to elevated turbulence conditions with free-stream turbulence intensity ranging from 0.2–6.0 percent. A simplified test condition on a flat plate is conducted with two discrete regions having different surface roughness. The leading edge roughness is comprised of a sandpaper strip or a single cylinder. The downstream surface is either smooth or covered with sandpaper of grit sizes ranging from 100 ∼ 40 (Ra = 37 ∼ 119 μm). Hot wire measurements are conducted in the boundary layer to study the flow structure. The results of this study verify that the height of the largest-scale roughness triggers an earlier transition even under elevated turbulence conditions and exerts a more dominant effect on flow and heat transfer than does the geometry of the roughness. Heat transfer enhancements of about 30 ∼ 40 percent over the entire test surface are observed. The vortical motion, generated by the backward facing step at the joint of two roughness regions, is believed to significantly increase momentum transport across the boundary layer and bring the elevated turbulence from the freestream towards the wall. No such long-lasting heat transfer phenomenon is observed in low FSTI cases even though vortex shedding also exists in the low turbulence cases. The heat transfer enhancement decreases, instead of increases, as the downstream roughness height increases.
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Sugioka, Hideaki, Zaiguo Fu, Takahiro Tsukahara, and Yasuo Kawaguchi. "PIV-PLIF Experiment on Modification of Turbulent Scalar Diffusion Near the Wall by Uniform Blowing." In ASME/JSME/KSME 2015 Joint Fluids Engineering Conference. American Society of Mechanical Engineers, 2015. http://dx.doi.org/10.1115/ajkfluids2015-25431.
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The transfer phenomena of wall turbulence are associated with the quasi ordered vortex structures, which are developed from small scale vortices near the wall. How to change the turbulent motion and turbulent transfer by modifying the condition of near wall is important for academic and industrial applications in the control of mass and heat transfers. In this study, we examined experimentally the effect on changing mass transfer in channel turbulence by uniform blowing from a porous wall. We used PIV/PLIF simultaneous measurement by mixing fluorescent dye into blown fluids to observe the spatial evolution of mass transfer in turbulence and analyzed flow fields from the view point of turbulence statistics. It was found that blowing enhanced fluctuation of disturbance and along with it, the coefficients of skin friction and mass transfer rate were increased. On the other hand, the isotropy of turbulence and turbulent Schmidt number were almost not changed. We concluded that there are universality in redistribution of turbulence energy and similar relationship between momentum and mass transfer.
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Ghosh, Kalyanjit, and R. J. Goldstein. "Effect of Inlet Skew on Heat/Mass Transfer From a Simulated Turbine Blade." In ASME 2011 Turbo Expo: Turbine Technical Conference and Exposition. ASMEDC, 2011. http://dx.doi.org/10.1115/gt2011-46543.
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Heat (mass) transfer experiments are conducted to study the effect of an inlet skew on a simulated gas-turbine blade placed in a linear cascade. The inlet skew simulates the relative motion between rotor and stator endwalls in a single turbine stage. The transverse motion of a belt, placed parallel to and upstream of the turbine cascade, generates the inlet skew. With the freestream velocity constant at approximately 16 m/sec, which results in a Reynolds number (based on the blade chord length of 0.184 m) of 1.8 × 105, a parametric study was conducted for three belt-to-freestream velocity ratios. The distribution of the Sherwood number on the suction surface of the blade shows that the inlet skew intensifies the generation of the horseshoe vortex close to the endwall region. This is associated with the development of a stronger passage vortex for a higher velocity ratio, which causes an earlier transition to turbulence. Corresponding higher mass transfer coefficients are measured between the mid-height of the blade and the endwall, at a mid-chord downstream location. However, a negligible variation in transport properties is measured above the two-dimensional region of the blade at the higher velocity ratios. In contrast, the inlet skew has a negligible effect on the distribution of the Sherwood number on the entire pressure surface of the blade. This is mainly because the skew is directed along the passage vortex, which is from the pressure surface of the airfoil to the suction surface of the adjacent airfoil.
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Gallegos, Ralph Kristoffer B., and Rajnish N. Sharma. "Flow Characteristics of a Narrow Rectangular Channel Equipped With a Flapping Flag." In ASME 2017 International Mechanical Engineering Congress and Exposition. American Society of Mechanical Engineers, 2017. http://dx.doi.org/10.1115/imece2017-70291.
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Recently, the use of flapping plates or ‘flags’ as vortex generators has gained attention for its potential application in heat transfer enhancement in channels. The motion of the flag generates additional turbulence which leads to enhanced heat transfer. However, very few reports deal with the turbulence characteristics inside a channel with flag vortex generators. This paper presents some flow turbulence properties experimentally measured behind a flapping flag. Using multi-hole pressure (cobra) probes, the flow properties behind a flag (M* = 0.42) were measured in a rectangular channel (aspect ratio, α = 1/3) at four levels of flow Reynolds number (Redh = 11.5k–19.7k). Results show that the spectral properties of the flow parameters are closely dependent on the flag oscillation properties. Depending on streamwise location and Redh, measurements reveal that the flag can generate as high as 20% turbulence intensity in the channel centerline, almost six times that of a bare channel at the same Redh. In addition, a streamwise location has been identified where the flag’s oscillation no longer influences the spectral characteristics of the flow. The insights gained from this study may serve as a basis for the design and analysis of systems using flags as turbulence enhancers.
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Godfrey, Aaron H., Robert E. Spall, and Byard D. Wood. "Computational Fluid Dynamics Analysis of Vertical Mixing in Algae Biofuel Raceways Through the Addition of Delta Wings at Angle-of-Incidence." In ASME 2012 Fluids Engineering Division Summer Meeting collocated with the ASME 2012 Heat Transfer Summer Conference and the ASME 2012 10th International Conference on Nanochannels, Microchannels, and Minichannels. American Society of Mechanical Engineers, 2012. http://dx.doi.org/10.1115/fedsm2012-72126.
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CFD calculations of experimental algae raceways under consideration for biofuel production studies were performed in an effort to assess the effectiveness of delta wing vortex formation as a means of enhancing vertical mixing. The impact of delta wings on the level of turbulence dissipation rate in these raceways was also investigated. All simulations were completed at a constant level of power input into the raceway. Velocity profiles as well as characteristic mixing times were used to analyze and quantify the vertical mixing both with and without delta wings. The velocity profiles and turbulent dissipation rate calculations suggest that delta wings are a viable method of increasing vertical motion. However, the mixing time results for the configuration of delta wings tested suggest that the additional mixing was insignificant to the raceway as a whole. Additional work on optimizing the use of delta wings is suggested.
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Elfert, M., M. P. Jarius, and B. Weigand. "Detailed Flow Investigation Using PIV in a Typical Turbine Cooling Geometry With Ribbed Walls." In ASME Turbo Expo 2004: Power for Land, Sea, and Air. ASMEDC, 2004. http://dx.doi.org/10.1115/gt2004-53566.
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In a stationary two-pass coolant channel system the fluid flow is investigated experimentally using the PIV (Particle Image Velocimetry). The cooling system consists of a trapezoidal leading edge channel, a 180 deg. bend and an almost rectangular second channel. The cross sections of the channels were adapted to the shape of a typical turbine blade. It has ribbed walls in both channels to enhance heat transfer performance. Ribs are placed at the top and bottom walls of the channels. The system was analyzed at the German Aerospace Center (DLR) with a small scaled model and at the Institute of Aerospace Thermodynamics (ITLR) of the Stuttgart University with a large scaled model to ease near rib flow analysis. Heat transfer results are not the objective of this paper, they are investigation topics of the ITLR which is in close cooperation [SCHUBERT (2003)]. At DLR presently rotation effects are studied. As a first step to understand the existing flow phenomena, the system is analyzed in non-rotating mode. During future work it will rotate about an axis orthogonal to the centreline of the straight passes. The results shown in this paper demonstrate the effect of the 180° bend with isothermal flow condition excluding any buoyancy. Turbulent channel flow with a REYNOLDS number of 40,000, derived with the hydraulic diameter of the second pass, was investigated. Two models either with smooth or ribbed walls were investigated. Some kinds of flow visualizations were conducted such as oil flow visualization technique for obtaining wall streamlines and laser light sheet visualization technique to detect vortex structures and separations. The results presented in this paper clarify the complex flow situation given by the two-pass system with the inherent turn. Especially in the bend area separation regions and vortices with high local turbulence are apparent. The presence of ribs changes the fluid motion by generating additional vortices impinging the leading and trailing wall. This very demanding measuring task represents a benchmark test case for the application of PIV and later of Stereo PIV, respectively.
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Ye, Lin, Cun-liang Liu, Hai-yong Liu, Hui-ren Zhu, and Jian-xia Luo. "Investigations on the Influence of Rib Orientation Angle on Film Cooling Performance of Compound Holes." In ASME Turbo Expo 2018: Turbomachinery Technical Conference and Exposition. American Society of Mechanical Engineers, 2018. http://dx.doi.org/10.1115/gt2018-75794.
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To investigate the effects of the inclined ribs on internal flow structure in film hole and the film cooling performance on outer surface, experimental and numerical studies are conducted on the effects of rib orientation angle on film cooling of compound cylindrical holes. Three coolant channel cases, including two ribbed cross-flow channels (135° and 45° angled ribs) and the plenum case, are studied under three blowing ratios (0.5, 1.0 and 2.0). 2D contours of film cooling effectiveness as well as heat transfer coefficient were measured by transient liquid crystal measurement technique (TLC). The steady RANS simulations with realizable k-ε turbulence model and enhanced wall treatment were performed. The results show that the spanwise width of film coverage is greatly influenced by the rib orientation angle. The spanwise width of the 45° rib case is obviously larger than that of the 135° rib case under lower blowing ratios. When the blowing ratio is 1.0, the area-averaged cooling effectiveness of the 135° rib case and the 45° rib case are higher than that of the plenum case by 38% and 107%, respectively. With the increase of blowing ratio, the film coverage difference between different rib orientation cases becomes smaller. The 45° rib case also produces higher heat transfer coefficient, which is higher than the 135° rib case by 3.4–8.7% within the studied blowing ratio range. Furthermore, the discharge coefficient of the 45° rib case is the lowest among the three cases. The helical motion of coolant flow is observed in the hole of 45° rib case. The jet divides into two parts after being blown out of the hole due to this motion, which induces strong velocity separation and loss. For the 135° rib case, the vortex in the upper half region of the secondary-flow channel rotates in the same direction with the hole inclination direction, which leads to the straight streamlines and thus results in lower loss and higher discharge coefficient.
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Elfert, M., M. Voges, and J. Klinner. "Detailed Flow Investigation Using PIV in a Rotating Square-Sectioned Two-Pass Cooling System With Ribbed Walls." In ASME Turbo Expo 2008: Power for Land, Sea, and Air. ASMEDC, 2008. http://dx.doi.org/10.1115/gt2008-51183.
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In a 2-pass cooling system the pressure driven air flow distribution is investigated experimentally using the non-intrusive PIV Technique. The generic model as part of a complex and sophisticated cooling system consists of two square-sectioned ducts with a length of 20 diameters and an inherent 180 degree bend. The system has been investigated basically with smooth walls (case 0) and, later on, with two different kinds of ribbed walls in both legs. Ribs are applied to enhance the cooling performance; they are placed on two opposite walls of both legs in a symmetric (case A) and an asymmetric manner (case B), respectively. The ribs are inclined with an angle of 45 degrees versus the duct axis (i.e. main flow direction). The applied rib lay-out is well-proved and optimized with respect to heat transfer improvement and the inherent pressure drop increase. The system rotates about an axis orthogonal to the centreline of the straight passes. The configuration was analyzed with the planar the two-component Particle Image Velocimetry (2C PIV), which is capable of obtaining complete maps of the instantaneous as well as the averaged flow field even at high turbulence levels, which are typically present within duct turns, near ribs and, above all, during rotation. The presented investigations were conducted in stationary and rotating mode. Especially in the bend region separation phenomena and vortices with high local turbulence are apparent. The presence of ribs changes the fluid motion by generating additional vortices impinging the side walls. Flow visualization with injected oil smoke using the laser light sheet visualization technique was helpful to detect vortex structures and separations. Especially in the bend area separation regions and vortices with high local turbulence are apparent. The results shown in this paper demonstrate the effect of the 180 degree bend in combination with the two rib turbulator geometries for isothermal flow conditions excluding any buoyancy with and without rotation. Turbulent channel flow was investigated at a Reynolds number of 50,000, derived with the hydraulic diameter of the pass, non-rotating and at a rotation number of 0.02 which was chosen still moderate. Engine relevant rotation numbers are in order of .1 or higher. A reconstruction of model mountings will allow higher values for the next tests. Future work will expand to higher rotational speed and, also, will include buoyancy effects. This investigation shall help to clarify the complex flow phenomena due to the interaction of several vortices, present in two-pass cooling systems. The flow maps obtained with PIV are of good quality and high spatial resolution and therefore provide a test case for the development and validation of numerical simulation tools like the DLR flow solver TRACE which is not a topic of this paper.
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Sabatino, D. R., and C. R. Smith. "Boundary Layer Influence on the Unsteady Horseshoe Vortex Flow and Surface Heat Transfer." In ASME Turbo Expo 2007: Power for Land, Sea, and Air. ASMEDC, 2007. http://dx.doi.org/10.1115/gt2007-27633.
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The spatial-temporal flow-field and associated surface heat transfer within the leading edge, end-wall region of a bluff body were examined using both particle image velocimetry and thermochromic liquid crystal temperature measurements. The horseshoe vortex system in the end-wall region is mechanistically linked to the upstream boundary layer unsteadiness. Hairpin vortex packets, associated with turbulent boundary layer bursting behavior, amalgamate with the horseshoe vortex resulting in unsteady strengthening and streamwise motion. The horseshoe vortex unsteadiness exhibits two different natural frequencies: one associated with the transient motion of the horseshoe vortex, and the other with the transient surface heat transfer. Comparable unsteadiness occurs in the end-wall region of the more complex airfoil geometry of a linear turbine cascade. To directly compare the horseshoe vortex behavior around a turning airfoil to that of a simple bluff body, a length scale based on the maximum airfoil thickness is proposed.
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Sugisaki, Daisuke, Masahiro Motosuke, and Shinji Honami. "Heat Transfer and Flow Characteristics Due to Interaction of Longitudinal Vortices by Vortex Generator Array." In ASME Turbo Expo 2007: Power for Land, Sea, and Air. ASMEDC, 2007. http://dx.doi.org/10.1115/gt2007-28189.
Full textAbstract:
This paper describes the turbulent heat transfer and the flow characteristics of the longitudinal vortices downstream of vortex generator array on the flat surface. Understanding on the heat transfer and flow characteristics is strongly required from the viewpoint of the heat transfer enhancement in an actual turbine blade design. The experiment was conducted in the test section of the wind tunnel which had a rectangular cross section and length of 2000mm. The reference velocity at the test section was 16 m/s and Reynolds number based on the momentum thickness was 1670. An array of the vortex generators with equal and/or unequal wing height was installed in the turbulent boundary layer. The experiments of the heat transfer on the flat surface were conducted by using the temperature sensitive liquid crystal. The surface of the test section was heated electrically by a thin stainless steel foil. The calibration of the hue of the liquid crystal and temperature was made by Neural Network method. Nusselt number corresponding to the turbulent heat transfer downstream of the array of the vortex generators is strongly affected by the longitudinal vortex motion. The local heat transfer depends on arrangement of the unequal wings of the vortex generator in co-rotating configuration. It is quite interesting that the longitudinal vortex located in the region of downwash motion of the adjacent vortex plays an important role in the merging process of the vortices. In conclusion, the array of the vortex generators is an effective device which can control the heat transfer and flow characteristics in the actual turbine blade cooling design.