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Karen A. Thole - One of the best experts on this subject based on the ideXlab platform.
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Thermal Field Measurements for a Shaped Hole at Low and High Freestream Turbulence Intensity
Journal of Turbomachinery, 2016Co-Authors: Robert P. Schroeder, Karen A. TholeAbstract:Shaped holes are increasingly selected for airfoil cooling in gas turbines due to their superior performance over that of cylindrical holes, especially at high blowing ratios. The performance of shaped holes is regarded to be the result of the diffused outlet, which slows and laterally spreads coolant, causing coolant to remain close to the wall. However, few thermal field measurements exist to verify this behavior at high blowing ratio or to evaluate how high Freestream turbulence alters the coolant distribution in jets from shaped holes. The present study reports measured thermal fields, along with measured flowfields, for a shaped hole at blowing ratios up to three at both low and high Freestream turbulence intensities of 0.5% and 13.2%. Thermal fields at low Freestream turbulence intensity showed that the coolant jet was initially attached, but far downstream of the hole the jet lifted away from the surface due to the counter-rotating vortex pair. Elevated Freestream turbulence intensity was found to cause strong dilution of the coolant jet and also increased dispersion, almost exclusively in the lateral as opposed to the vertical direction. Dominance of lateral dispersion was due to the influence of the wall on Freestream eddies, as indicated from changes in turbulent shear stress between the low and high Freestream turbulence cases.
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Thermal Field Measurements for a Shaped Hole at Low and High Freestream Turbulence Intensity
Volume 5C: Heat Transfer, 2016Co-Authors: Robert P. Schroeder, Karen A. TholeAbstract:Shaped holes are increasingly selected for airfoil cooling in gas turbines due to their superior performance over that of cylindrical holes, especially at high blowing ratios. The performance of shaped holes is regarded to be result of the diffused outlet which slows and laterally-spreads coolant, causing coolant to remain close to the wall. However, few thermal field measurements exist to verify this behavior at high blowing ratio or to evaluate how high Freestream turbulence alters the coolant distribution in jets from shaped holes. The present study reports measured thermal fields, along with measured flowfields, for a shaped hole at blowing ratios up to 3 at both low and high Freestream turbulence intensities of 0.5% and 13.2%. Thermal fields at low Freestream turbulence intensity showed that the coolant jet was initially attached, but far downstream of the hole the jet lifted away from the surface due to the counter-rotating vortex pair. Elevated Freestream turbulence intensity was found to cause strong dilution of the coolant jet and also increased dispersion, almost exclusively in the lateral as opposed to the vertical direction. Dominance of lateral dispersion was due to the influence of the wall on Freestream eddies, as indicated from changes in turbulent shear stress between the low and high Freestream turbulence cases.
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the effects of Freestream turbulence turbulence length scale and exit reynolds number on turbine blade heat transfer in a transonic cascade
Journal of Turbomachinery-transactions of The Asme, 2011Co-Authors: J S Carullo, Karen A. Thole, S Nasir, R D Cress, Luzeng J Zhang, Hee Koo MoonAbstract:This paper experimentally investigates the effect of high Freestream turbulence intensity, turbulence length scale, and exit Reynolds number on the surface heat transfer distribution of a turbine blade at realistic engine Mach numbers. Passive turbulence grids were used to generate Freestream turbulence levels of 2%, 12%, and 14% at the cascade inlet. The turbulence grids produced length scales normalized by the blade pitches of 0.02, 0.26, and 0.41, respectively. Surface heat transfer measurements were made at the midspan of the blade using thin film gauges. Experiments were performed at the exit Mach numbers of 0.55, 0.78, and 1.03, which represent flow conditions below, near, and above nominal conditions. The exit Mach numbers tested correspond to exit Reynolds numbers of 6 × 10 5 , 8 × 10 5 , and 11 × 10 5 , based on true chord. The experimental results showed that the high Freestream turbulence augmented the heat transfer on both the pressure and suction sides of the blade as compared with the low Freestream turbulence case. At nominal conditions, exit Mach 0.78, average heat transfer augmentations of 23% and 35% were observed on the pressure side and suction side of the blade, respectively.
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the effects of Freestream turbulence turbulence length scale and exit reynolds number on turbine blade heat transfer in a transonic cascade
ASME Turbo Expo 2007: Power for Land Sea and Air, 2007Co-Authors: J S Carullo, Karen A. Thole, S Nasir, R D Cress, Luzeng J Zhang, Hee Koo MoonAbstract:This paper experimentally investigates the effect of high Freestream turbulence intensity, turbulence length scale, and exit Reynolds number on the surface heat transfer distribution of a turbine blade at realistic engine Mach numbers. Passive turbulence grids were used to generate Freestream turbulence levels of 2%, 12%, and 14% at the cascade inlet. The turbulence grids produced length scales normalized by the blade pitch of 0.02, 0.26, and 0.41, respectively. Surface heat transfer measurements were made at the midspan of the blade using thin film gauges. Experiments were performed at exit Mach numbers of 0.55, 0.78 and 1.03 which represent flow conditions below, near, and above nominal conditions. The exit Mach numbers tested correspond to exit Reynolds numbers of 6 × 105 , 8 × 105 , and 11 × 105 , based on true chord. The experimental results showed that the high Freestream turbulence augmented the heat transfer on both the pressure and suction sides of the blade as compared to the low Freestream turbulence case. At nominal conditions, exit Mach 0.78, average heat transfer augmentations of 23% and 35% were observed on the pressure side and suction side of the blade, respectively.© 2007 ASME
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Elevated Freestream turbulence effects on heat transfer for a gas turbine vane
International Journal of Heat and Fluid Flow, 2002Co-Authors: Karen A. Thole, R. W. Radomsky, M.b. Kang, Atul KohliAbstract:Abstract High Freestream turbulence levels have been shown to greatly augment the heat transfer along a gas turbine airfoil, particularly for the first stage nozzle guide vane. For this study, augmentations in convective heat transfer have been measured for a first stage turbine vane in the stagnation region, along the mid-span, and along the platform resulting from an approach Freestream turbulence level of 19.5%. In addition to quantifying surface heat transfer, boundary layer measurements have been made to better understand high Freestream turbulence effects. Although there are a number of correlations that have been developed for scaling Freestream turbulence augmentations to heat transfer, the results of this study indicate that these correlations are not successful in predicting heat transfer for various regions along a turbine vane.
Forrest E. Ames - One of the best experts on this subject based on the ideXlab platform.
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Large Eddy Simulation of the Laminar Heat Transfer Augmentation on the Pressure Side of a Turbine Vane Under Freestream Turbulence
Journal of Turbomachinery, 2019Co-Authors: Yousef Kanani, Sumanta Acharya, Forrest E. AmesAbstract:Vane pressure side heat transfer is studied numerically using large eddy simulation (LES) on an aft-loaded vane with a large leading edge over a range of turbulence conditions. Numerical simulations are performed in a linear cascade at exit chord Reynolds number of Re = 5.1 × 105 at low (Tu ≈ 0.7%), moderate (Tu ≈ 7.9%), and high (Tu ≈ 12.4%) Freestream turbulence with varying length scales as prescribed by the experimental measurements of Varty and Ames (2016, “Experimental Heat Transfer Distributions Over an Aft Loaded Vane With a Large Leading Edge at Very High Turbulence Levels,” ASME Paper No. IMECE2016-67029). Heat transfer predictions on the vane pressure side are in a very good agreement with the experimental measurements and the heat transfer augmentation due to the Freestream turbulence is well captured. At Tu ≈ 12.4%, Freestream turbulence enhances the Stanton number on the pressure surface without boundary layer transition to turbulence by a maximum of about 50% relative to the low Freestream turbulence case. Higher Freestream turbulence generates elongated structures and high-velocity streaks wrapped around the leading edge that contain significant energy. Amplification of the velocity streaks is observed further downstream with max rms of 0.3 near the trailing edge but no transition to turbulence or formation of turbulence spots is observed on the pressure side. The heat transfer augmentation at the higher Freestream turbulence is primarily due to the initial amplification of the low-frequency velocity perturbations inside the boundary layer that persist along the entire chord of the airfoil. Stanton numbers appear to scale with the streamwise velocity fluctuations inside the boundary layer.
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LES Study of the Laminar Heat Transfer Augmentation on the Pressure Side of a Turbine Vane Under Freestream Turbulence
Volume 5C: Heat Transfer, 2018Co-Authors: Yousef Kanani, Sumanta Acharya, Forrest E. AmesAbstract:Vane pressure side heat transfer is studied numerically using Large Eddy Simulation (LES) on an aft loaded vane with a large leading edge over a range of turbulence conditions. Numerical simulations are performed in a linear cascade at exit chord Reynolds number of Re = 5.1 × 105 at low (Tu≈0.7%), moderate (Tu≈7.9%) and high (Tu≈12.4%) Freestream turbulence with varying length scales as prescribed by the experimental measurements of Varty and Ames (2016). Heat transfer predictions (i.e. Stanton number based on exit condition) on the vane pressure side are in a very good agreement with the experimental measurements and the heat transfer augmentation due to the Freestream turbulence is well captured. At Tu≈12.4%, Freestream turbulence enhances the Stanton number on the pressure surface without boundary layer transition to turbulence by a maximum of about 50% relative to the low Freestream turbulence case (Tu≈0.7%). Higher Freestream turbulence generates elongated structures and high-velocity streaks wrapped around the leading edge that contain significant energy. Amplification of the velocity streaks is observed further downstream with max r.m.s of 0.3 near the trailing edge but no transition to turbulence or formation of turbulence spots is observed on the pressure side. The heat transfer augmentation at the higher Freestream turbulence is primarily due to the initial amplification of the low-frequency velocity perturbations inside the boundary layer that persist along the entire chord of the airfoil. Stanton numbers appear to scale with the streamwise velocity fluctuations inside the boundary layer. Görtler vortices are not observed for this airfoil geometry.
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SIMULATIONS OF SLOT FILM-COOLING WITH Freestream ACCELERATION AND TURBULENCE
Journal of Turbomachinery, 2018Co-Authors: Yousef Kanani, Sumanta Acharya, Forrest E. AmesAbstract:Slot film cooling in an accelerating boundary layer with high Freestream turbulence is studied numerically using large eddy simulations (LES). Calculations are done for a symmetrical leading edge geometry with the slot fed by a plenum populated with pin fins. The synthetic eddy method is used to generate different levels of turbulence and length scales at the inflow cross-plane. Calculations are done for a Reynolds number of 250,000 and Freestream turbulence levels of 0.7%, 3.5%, 7.8%, and 13.7% to predict both film cooling effectiveness and heat transfer coefficient over the test surface. These conditions correspond to the experimental measurements of (Busche, M. L., Kingery, J. E., and Ames, F. E., 2014, “Slot Film Cooling in an Accelerating Boundary Layer With High Free-Stream Turbulence,” ASME Paper No. GT2014-25360.) Numerical results show good agreement with measurements and show the observed decay of thermal effectiveness and increase of Stanton number with turbulence intensity. Velocity and turbulence exiting the slot are nonuniform laterally due to the presence of pin fins in the plenum feeding the slot which creates a nonuniform surface temperature distribution. No transition to fully turbulent boundary layer is observed throughout the numerical domain. However, Freestream turbulence increases wall shear stress downstream driving the velocity profiles toward the turbulent profile and counteracts the laminarizing effects of the favorable pressure gradient. The effective Prandtl number decreases with Freestream turbulence. The temperature profiles deviate from the self-similar profile measured under low Freestream turbulence condition, reflecting the role of the increased diffusivity in the boundary layer at higher Freestream turbulence.
R. W. Radomsky - One of the best experts on this subject based on the ideXlab platform.
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Elevated Freestream turbulence effects on heat transfer for a gas turbine vane
International Journal of Heat and Fluid Flow, 2002Co-Authors: Karen A. Thole, R. W. Radomsky, M.b. Kang, Atul KohliAbstract:Abstract High Freestream turbulence levels have been shown to greatly augment the heat transfer along a gas turbine airfoil, particularly for the first stage nozzle guide vane. For this study, augmentations in convective heat transfer have been measured for a first stage turbine vane in the stagnation region, along the mid-span, and along the platform resulting from an approach Freestream turbulence level of 19.5%. In addition to quantifying surface heat transfer, boundary layer measurements have been made to better understand high Freestream turbulence effects. Although there are a number of correlations that have been developed for scaling Freestream turbulence augmentations to heat transfer, the results of this study indicate that these correlations are not successful in predicting heat transfer for various regions along a turbine vane.
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Detailed Boundary Layer Measurements on a Turbine Stator Vane at Elevated Freestream Turbulence Levels
Volume 3: Heat Transfer; Electric Power; Industrial and Cogeneration, 2001Co-Authors: R. W. Radomsky, Karen A. TholeAbstract:High Freestream turbulence levels have been shown to greatly augment the heat transfer on a gas turbine airfoil. To better understand these effects, this study has examined the effects elevated Freestream turbulence levels have on the boundary layer development along a stator vane airfoil. Low Freestream turbulence measurements (0.6%) were performed as a baseline for comparison to measurements at combustor simulated turbulence levels (19.5%). A two-component LDV system was used for detailed boundary layer measurements of both the mean and fluctuating velocities on the pressure and suction surfaces. Although the mean velocity profiles appeared to be more consistent with laminar profiles, large velocity fluctuations were measured in the boundary layer along the pressure side at the high Freestream turbulence conditions. Along the suction side, transition occurred further upstream due to Freestream turbulence.© 2001 ASME
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Detailed Boundary Layer Measurements on a Turbine Stator Vane at Elevated Freestream Turbulence Levels
Journal of Turbomachinery, 2001Co-Authors: R. W. Radomsky, Karen A. TholeAbstract:High Freestream turbulence levels have been shown to greatly augment the heat transfer on a gas turbine airfoil. To better understand these effects, this study has examined the effects elevated Freestream turbulence levels have on the boundary layer development along a stator vane airfoil. Low Freestream turbulence measurements (0.6 percent) were performed as a baseline for comparison to measurements at combustor simulated turbulence levels (19.5 percent). A two-component LDV system was used for detailed boundary layer measurements of both the mean and fluctuating velocities on the pressure and suction surfaces. Although the mean velocity profiles appeared to be more consistent with laminar profiles, large velocity fluctuations were measured in the boundary layer along the pressure side at the high Freestream turbulence conditions. Along the suction side, transition occurred further upstream due to Freestream turbulence.
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High Freestream Turbulence Effects on Endwall Heat Transfer for a Gas Turbine Stator Vane
Volume 3: Heat Transfer; Electric Power; Industrial and Cogeneration, 2000Co-Authors: R. W. Radomsky, Karen A. TholeAbstract:High Freestream turbulence along a gas turbine airfoil and strong secondary flows along the endwall have both been reported to significantly increase convective heat transfer. This study superimposes high Freestream turbulence on the naturally occurring secondary flow vortices to determine the effects on the flowfield and the endwall convective heat transfer. Measured flowfield and heat transfer data were compared between low Freestream turbulence levels (0.6%) and combustor simulated turbulence levels (19.5%) that were generated using an active grid. These experiments were conducted using a scaled-up, first stage stator vane geometry. Infrared thermography was used to measure surface temperatures on a constant heat flux plate placed on the endwall surface. Laser Doppler velocimeter (LDV) measurements were performed of all three components of the mean and fluctuating velocities of the leading edge horse-shoe vortex. The results indicate that the mean flowfields for the leading edge horseshoe vortex were similar between the low and high Freestream turbulence cases. High turbulence levels in the leading edge-endwall juncture were attributed to a vortex unsteadiness for both the low and high Freestream tubulence cases. While, in general, the high Freestream turbulence increased the endwall heat transfer, low augmentations were found to coincide with the regions having the most intense vortex motions.Copyright © 2000 by ASME
Yousef Kanani - One of the best experts on this subject based on the ideXlab platform.
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Large Eddy Simulation of the Laminar Heat Transfer Augmentation on the Pressure Side of a Turbine Vane Under Freestream Turbulence
Journal of Turbomachinery, 2019Co-Authors: Yousef Kanani, Sumanta Acharya, Forrest E. AmesAbstract:Vane pressure side heat transfer is studied numerically using large eddy simulation (LES) on an aft-loaded vane with a large leading edge over a range of turbulence conditions. Numerical simulations are performed in a linear cascade at exit chord Reynolds number of Re = 5.1 × 105 at low (Tu ≈ 0.7%), moderate (Tu ≈ 7.9%), and high (Tu ≈ 12.4%) Freestream turbulence with varying length scales as prescribed by the experimental measurements of Varty and Ames (2016, “Experimental Heat Transfer Distributions Over an Aft Loaded Vane With a Large Leading Edge at Very High Turbulence Levels,” ASME Paper No. IMECE2016-67029). Heat transfer predictions on the vane pressure side are in a very good agreement with the experimental measurements and the heat transfer augmentation due to the Freestream turbulence is well captured. At Tu ≈ 12.4%, Freestream turbulence enhances the Stanton number on the pressure surface without boundary layer transition to turbulence by a maximum of about 50% relative to the low Freestream turbulence case. Higher Freestream turbulence generates elongated structures and high-velocity streaks wrapped around the leading edge that contain significant energy. Amplification of the velocity streaks is observed further downstream with max rms of 0.3 near the trailing edge but no transition to turbulence or formation of turbulence spots is observed on the pressure side. The heat transfer augmentation at the higher Freestream turbulence is primarily due to the initial amplification of the low-frequency velocity perturbations inside the boundary layer that persist along the entire chord of the airfoil. Stanton numbers appear to scale with the streamwise velocity fluctuations inside the boundary layer.
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LES Study of the Laminar Heat Transfer Augmentation on the Pressure Side of a Turbine Vane Under Freestream Turbulence
Volume 5C: Heat Transfer, 2018Co-Authors: Yousef Kanani, Sumanta Acharya, Forrest E. AmesAbstract:Vane pressure side heat transfer is studied numerically using Large Eddy Simulation (LES) on an aft loaded vane with a large leading edge over a range of turbulence conditions. Numerical simulations are performed in a linear cascade at exit chord Reynolds number of Re = 5.1 × 105 at low (Tu≈0.7%), moderate (Tu≈7.9%) and high (Tu≈12.4%) Freestream turbulence with varying length scales as prescribed by the experimental measurements of Varty and Ames (2016). Heat transfer predictions (i.e. Stanton number based on exit condition) on the vane pressure side are in a very good agreement with the experimental measurements and the heat transfer augmentation due to the Freestream turbulence is well captured. At Tu≈12.4%, Freestream turbulence enhances the Stanton number on the pressure surface without boundary layer transition to turbulence by a maximum of about 50% relative to the low Freestream turbulence case (Tu≈0.7%). Higher Freestream turbulence generates elongated structures and high-velocity streaks wrapped around the leading edge that contain significant energy. Amplification of the velocity streaks is observed further downstream with max r.m.s of 0.3 near the trailing edge but no transition to turbulence or formation of turbulence spots is observed on the pressure side. The heat transfer augmentation at the higher Freestream turbulence is primarily due to the initial amplification of the low-frequency velocity perturbations inside the boundary layer that persist along the entire chord of the airfoil. Stanton numbers appear to scale with the streamwise velocity fluctuations inside the boundary layer. Görtler vortices are not observed for this airfoil geometry.
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SIMULATIONS OF SLOT FILM-COOLING WITH Freestream ACCELERATION AND TURBULENCE
Journal of Turbomachinery, 2018Co-Authors: Yousef Kanani, Sumanta Acharya, Forrest E. AmesAbstract:Slot film cooling in an accelerating boundary layer with high Freestream turbulence is studied numerically using large eddy simulations (LES). Calculations are done for a symmetrical leading edge geometry with the slot fed by a plenum populated with pin fins. The synthetic eddy method is used to generate different levels of turbulence and length scales at the inflow cross-plane. Calculations are done for a Reynolds number of 250,000 and Freestream turbulence levels of 0.7%, 3.5%, 7.8%, and 13.7% to predict both film cooling effectiveness and heat transfer coefficient over the test surface. These conditions correspond to the experimental measurements of (Busche, M. L., Kingery, J. E., and Ames, F. E., 2014, “Slot Film Cooling in an Accelerating Boundary Layer With High Free-Stream Turbulence,” ASME Paper No. GT2014-25360.) Numerical results show good agreement with measurements and show the observed decay of thermal effectiveness and increase of Stanton number with turbulence intensity. Velocity and turbulence exiting the slot are nonuniform laterally due to the presence of pin fins in the plenum feeding the slot which creates a nonuniform surface temperature distribution. No transition to fully turbulent boundary layer is observed throughout the numerical domain. However, Freestream turbulence increases wall shear stress downstream driving the velocity profiles toward the turbulent profile and counteracts the laminarizing effects of the favorable pressure gradient. The effective Prandtl number decreases with Freestream turbulence. The temperature profiles deviate from the self-similar profile measured under low Freestream turbulence condition, reflecting the role of the increased diffusivity in the boundary layer at higher Freestream turbulence.
Jean-pierre Hickey - One of the best experts on this subject based on the ideXlab platform.
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Boundary layer turbulence and Freestream turbulence interface, turbulent spot and Freestream turbulence interface, laminar boundary layer and Freestream turbulence interface
Physics of Fluids, 2019Co-Authors: James M. Wallace, Jean-pierre HickeyAbstract:We study the boundary-layer turbulence and Freestream turbulence interface (BTFTI), the turbulent spot and Freestream turbulence interface (TSFTI), and the laminar boundary-layer and Freestream turbulence interface (LBFTI) using direct simulation. Grid spacings in the Freestream are less than 1 Kolmogorov length scale during transition. Probability density functions of temperature and its derivatives are used to select the interface identification threshold, corroborated by a vorticity-based method. The interfaces so detected are confirmed to be physical a posteriori by the distinctive quasi-step-jump behavior in the swirling strength and temperature statistics along traverses normal to the BTFTI and TSFTI. No interface-normal inflection is detected across the LBFTI for either swirling strength, temperature, vorticity magnitude, Reynolds shear stress, streamwise velocity, normal velocity, or turbulence kinetic energy. The present direct numerical simulation data thus cast serious doubts on the shear-sheltering hypothesis/theory, which asserts that a subset of Freestream fluctuations is blocked by the LBFTI. In the early stage of transition, quasi-spanwise structures exist on the LBFTI. The TSFTI shape is dominated by head prints of concentrated hairpin vortices. Further downstream, the BTFTI geometry is strongly modulated by groves of hairpin vortices (the boundary layer large-scale motions) with a distinct streamwise preferential orientation. Streamwise velocity and turbulence kinetic energy only exhibit minor plateaus (rather than quasi-step-jump) across the BTFTI and the TSFTI. We emphasize that it is more meaningful and important to acquire reproducible and reliable interface-normal statistics prior to considering any plausible substructures and elusive transient dynamics of the BTFTI, TSFTI, and LBFTI.We study the boundary-layer turbulence and Freestream turbulence interface (BTFTI), the turbulent spot and Freestream turbulence interface (TSFTI), and the laminar boundary-layer and Freestream turbulence interface (LBFTI) using direct simulation. Grid spacings in the Freestream are less than 1 Kolmogorov length scale during transition. Probability density functions of temperature and its derivatives are used to select the interface identification threshold, corroborated by a vorticity-based method. The interfaces so detected are confirmed to be physical a posteriori by the distinctive quasi-step-jump behavior in the swirling strength and temperature statistics along traverses normal to the BTFTI and TSFTI. No interface-normal inflection is detected across the LBFTI for either swirling strength, temperature, vorticity magnitude, Reynolds shear stress, streamwise velocity, normal velocity, or turbulence kinetic energy. The present direct numerical simulation data thus cast serious doubts on the shear-shelt...
