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John K. Eaton - One of the best experts on this subject based on the ideXlab platform.

  • Measurements in discrete hole film cooling behavior with periodic freestream unsteadiness
    Experiments in Fluids, 2018
    Co-Authors: Daniel D. Borup, Christopher J Elkins, John K. Eaton
    Abstract:

    Magnetic resonance imaging (MRI) techniques were used to investigate a discrete, $$30^{\circ }$$ 30 ∘ -inclined round jet in crossflow subjected to periodic freestream unsteadiness. The freestream perturbations were generated by an oscillating airfoil upstream of the jet. The experiment operated at a Strouhal number of 0.014, channel Reynolds number of 25,000, hole Reynolds number of 2900, and jet blowing ratio of unity. 3D phase locked velocity measurements were obtained over the entire channel using magnetic resonance velocimetry (MRV). 3D time-averaged temperature measurements were acquired using magnetic resonance thermometry (MRT), along with phase-locked temperature measurements in the 2D centerplane of the channel and jet. The freestream flow just upstream of the jet was characterized by streamwise velocities ranging from $$0.88 U_\text {bulk}$$ 0.88 U bulk to $$1.23 U_\text {bulk}$$ 1.23 U bulk and wall-normal velocities from $$-0.11 U_\text {bulk}$$ - 0.11 U bulk to $$0.02 U_\text {bulk}$$ 0.02 U bulk . Flow inside the hole was observed to be insensitive to the freestream fluctuations, as velocities and temperatures in the hole remained largely unchanged throughout the cycle. Outside the hole, changes to the streamwise velocity produced an oscillating jet blowing ratio that led to the lengthening and shortening of the counter-rotating vortex pair (CVP) as well as a varying degree of coolant separation from the film cooled wall. During one portion of the cycle, downwashing freestream flow (i.e., flow with negative wall-normal velocities) promoted strong re-attachment and lateral spreading of the jet. Mean, spanwise-averaged film cooling Effectiveness values were compared to those of an earlier experiment with a steady freestream and identical geometry, Reynolds number, and blowing ratio. Film cooling performance in the near-hole region was higher with steady freestream flow. However, at downstream locations, the downward transport of coolant by the periodic downwashing flow led to a higher mean Surface Effectiveness than in the steady case.

  • the effect of land taper angle on trailing edge slot film cooling
    ASME Turbo Expo 2014: Turbine Technical Conference and Exposition, 2014
    Co-Authors: Julia Ling, Christopher J Elkins, John K. Eaton
    Abstract:

    Trailing edge slot film cooling is a widely used method of protecting the thin trailing edge of turbine blades from hot gas impingement. The structures that separate the slots, known as “lands,” come in a variety of configurations which can be broadly classified as either “tapered” or “straight.” This paper examines the effect of the land taper angle on the mixing of the coolant flow with the main flow by comparing three configurations: a case with straight lands, a previously reported case with slightly tapered lands, and a case with strongly tapered lands. In each case, the slot width and the land width at the plane of the slot exit are kept constant. For each configuration, the mean volumetric coolant concentration distribution and 3-component velocity field were measured using Magnetic Resonance Imaging techniques. It is shown that the land taper angle has a strong effect on the mean flow features and coolant Surface Effectiveness. Furthermore, the impact of the lands configuration on the flow field and concentration distribution is seen not just in the cutback region, but also in the wake of the blade.Copyright © 2014 by ASME

  • optimal turbulent schmidt number for rans modeling of trailing edge slot film cooling
    Journal of Engineering for Gas Turbines and Power-transactions of The Asme, 2014
    Co-Authors: Julia Ling, Christopher J Elkins, John K. Eaton
    Abstract:

    It has been previously demonstrated that Reynolds Averaged Navier Stokes (RANS) simulations do not accurately capture the mixing between the coolant flow and the main flow in trailing edge slot film cooling configurations. Most RANS simulations use a fixed turbulent Schmidt number of either 0.7 or 0.85 to determine the turbulent scalar flux, based on the values for canonical flows. This paper explores the extent to which RANS predictions can be improved by modifying the value of the turbulent Schmidt number. Experimental mean 3D velocity and coolant concentration data obtained using Magnetic Resonance Imaging techniques are used to evaluate the accuracy of RANS simulations. A range of turbulent Schmidt numbers from 0.05 to 1.05 is evaluated and the optimal turbulent Schmidt number for each case is determined using an integral error metric which accounts for the difference between RANS and experiment throughout a 3-dimensional region of interest. The resulting concentration distribution is compared in detail with the experimentally measured coolant concentration distribution to reveal where the fixed turbulent Schmidt number assumption fails. It is shown that the commonly used turbulent Schmidt number of 0.85 over-predicts the Surface Effectiveness in all cases, particularly when the k-omega SST model is employed, and that a lower value of the turbulent Schmidt number can improve predictions.Copyright © 2014 by ASME

  • An inclined jet in crossflow under the effect of streamwise pressure gradients
    Experiments in Fluids, 2013
    Co-Authors: Filippo Coletti, Christopher J Elkins, John K. Eaton
    Abstract:

    An inclined turbulent jet discharging a passive scalar into a turbulent crossflow is investigated under conditions of favorable, zero and adverse streamwise pressure gradient. Experiments are conducted in water by means of magnetic resonance velocimetry and magnetic resonance concentration measurements. The velocity ratio and density ratio are equal to one for all cases. The flow configuration is relevant to film cooling technology, the molecular properties of the fluid being immaterial in the fully turbulent regime. Under favorable pressure gradient (FPG), the streamwise acceleration tilts the jet trajectory toward the wall, which would be beneficial for the film cooling performance. However, the counter-rotating vortex pair is strengthened in the accelerating flow by streamwise stretching. Also, the crossflow boundary layer is significantly thickened by increasingly adverse pressure gradient, which affects the mass transfer from the jet. Overall, the more intense counter-rotating vortices and the thinner boundary layer associated with increasingly FPG enhance the scalar dispersion into the main flow, hampering the film cooling performance in terms of Surface Effectiveness.

  • Effects of varying Reynolds number, blowing ratio, and internal geometry on trailing edge cutback film cooling
    Experiments in Fluids, 2012
    Co-Authors: Michael J. Benson, Christopher J Elkins, Sayuri D. Yapa, Julia B. Ling, John K. Eaton
    Abstract:

    Three-dimensional mean velocity and concentration fields have been measured for a water flow in a pressure side cutback trailing edge film cooling geometry consisting of rectangular film cooling slots separated by tapered lands. Three-component mean velocities were measured with conventional magnetic resonance velocimetry, while time-averaged concentration distributions were measured with a magnetic resonance concentration technique for flow at two Reynolds numbers ( Re ) differing by a factor of 2, three blowing ratios, and with and without an internal pin fin array in the coolant feed channel. The results show that the flows are essentially independent of Re for the regime tested in terms of the film cooling Surface Effectiveness, normalized velocity profiles, and normalized mean streamwise vorticity. Blowing ratio changes had a larger effect, with higher blowing ratios resulting in Surface Effectiveness improvements at downstream locations. The addition of a pin fin array within the slot feed channel made the spanwise distribution of coolant at the Surface more uniform. Results are compared with transonic experiments in air at realistic density ratios described by Holloway et al. (2002a) .

Christopher J Elkins - One of the best experts on this subject based on the ideXlab platform.

  • Measurements in discrete hole film cooling behavior with periodic freestream unsteadiness
    Experiments in Fluids, 2018
    Co-Authors: Daniel D. Borup, Christopher J Elkins, John K. Eaton
    Abstract:

    Magnetic resonance imaging (MRI) techniques were used to investigate a discrete, $$30^{\circ }$$ 30 ∘ -inclined round jet in crossflow subjected to periodic freestream unsteadiness. The freestream perturbations were generated by an oscillating airfoil upstream of the jet. The experiment operated at a Strouhal number of 0.014, channel Reynolds number of 25,000, hole Reynolds number of 2900, and jet blowing ratio of unity. 3D phase locked velocity measurements were obtained over the entire channel using magnetic resonance velocimetry (MRV). 3D time-averaged temperature measurements were acquired using magnetic resonance thermometry (MRT), along with phase-locked temperature measurements in the 2D centerplane of the channel and jet. The freestream flow just upstream of the jet was characterized by streamwise velocities ranging from $$0.88 U_\text {bulk}$$ 0.88 U bulk to $$1.23 U_\text {bulk}$$ 1.23 U bulk and wall-normal velocities from $$-0.11 U_\text {bulk}$$ - 0.11 U bulk to $$0.02 U_\text {bulk}$$ 0.02 U bulk . Flow inside the hole was observed to be insensitive to the freestream fluctuations, as velocities and temperatures in the hole remained largely unchanged throughout the cycle. Outside the hole, changes to the streamwise velocity produced an oscillating jet blowing ratio that led to the lengthening and shortening of the counter-rotating vortex pair (CVP) as well as a varying degree of coolant separation from the film cooled wall. During one portion of the cycle, downwashing freestream flow (i.e., flow with negative wall-normal velocities) promoted strong re-attachment and lateral spreading of the jet. Mean, spanwise-averaged film cooling Effectiveness values were compared to those of an earlier experiment with a steady freestream and identical geometry, Reynolds number, and blowing ratio. Film cooling performance in the near-hole region was higher with steady freestream flow. However, at downstream locations, the downward transport of coolant by the periodic downwashing flow led to a higher mean Surface Effectiveness than in the steady case.

  • the effect of land taper angle on trailing edge slot film cooling
    ASME Turbo Expo 2014: Turbine Technical Conference and Exposition, 2014
    Co-Authors: Julia Ling, Christopher J Elkins, John K. Eaton
    Abstract:

    Trailing edge slot film cooling is a widely used method of protecting the thin trailing edge of turbine blades from hot gas impingement. The structures that separate the slots, known as “lands,” come in a variety of configurations which can be broadly classified as either “tapered” or “straight.” This paper examines the effect of the land taper angle on the mixing of the coolant flow with the main flow by comparing three configurations: a case with straight lands, a previously reported case with slightly tapered lands, and a case with strongly tapered lands. In each case, the slot width and the land width at the plane of the slot exit are kept constant. For each configuration, the mean volumetric coolant concentration distribution and 3-component velocity field were measured using Magnetic Resonance Imaging techniques. It is shown that the land taper angle has a strong effect on the mean flow features and coolant Surface Effectiveness. Furthermore, the impact of the lands configuration on the flow field and concentration distribution is seen not just in the cutback region, but also in the wake of the blade.Copyright © 2014 by ASME

  • optimal turbulent schmidt number for rans modeling of trailing edge slot film cooling
    Journal of Engineering for Gas Turbines and Power-transactions of The Asme, 2014
    Co-Authors: Julia Ling, Christopher J Elkins, John K. Eaton
    Abstract:

    It has been previously demonstrated that Reynolds Averaged Navier Stokes (RANS) simulations do not accurately capture the mixing between the coolant flow and the main flow in trailing edge slot film cooling configurations. Most RANS simulations use a fixed turbulent Schmidt number of either 0.7 or 0.85 to determine the turbulent scalar flux, based on the values for canonical flows. This paper explores the extent to which RANS predictions can be improved by modifying the value of the turbulent Schmidt number. Experimental mean 3D velocity and coolant concentration data obtained using Magnetic Resonance Imaging techniques are used to evaluate the accuracy of RANS simulations. A range of turbulent Schmidt numbers from 0.05 to 1.05 is evaluated and the optimal turbulent Schmidt number for each case is determined using an integral error metric which accounts for the difference between RANS and experiment throughout a 3-dimensional region of interest. The resulting concentration distribution is compared in detail with the experimentally measured coolant concentration distribution to reveal where the fixed turbulent Schmidt number assumption fails. It is shown that the commonly used turbulent Schmidt number of 0.85 over-predicts the Surface Effectiveness in all cases, particularly when the k-omega SST model is employed, and that a lower value of the turbulent Schmidt number can improve predictions.Copyright © 2014 by ASME

  • An inclined jet in crossflow under the effect of streamwise pressure gradients
    Experiments in Fluids, 2013
    Co-Authors: Filippo Coletti, Christopher J Elkins, John K. Eaton
    Abstract:

    An inclined turbulent jet discharging a passive scalar into a turbulent crossflow is investigated under conditions of favorable, zero and adverse streamwise pressure gradient. Experiments are conducted in water by means of magnetic resonance velocimetry and magnetic resonance concentration measurements. The velocity ratio and density ratio are equal to one for all cases. The flow configuration is relevant to film cooling technology, the molecular properties of the fluid being immaterial in the fully turbulent regime. Under favorable pressure gradient (FPG), the streamwise acceleration tilts the jet trajectory toward the wall, which would be beneficial for the film cooling performance. However, the counter-rotating vortex pair is strengthened in the accelerating flow by streamwise stretching. Also, the crossflow boundary layer is significantly thickened by increasingly adverse pressure gradient, which affects the mass transfer from the jet. Overall, the more intense counter-rotating vortices and the thinner boundary layer associated with increasingly FPG enhance the scalar dispersion into the main flow, hampering the film cooling performance in terms of Surface Effectiveness.

  • Effects of varying Reynolds number, blowing ratio, and internal geometry on trailing edge cutback film cooling
    Experiments in Fluids, 2012
    Co-Authors: Michael J. Benson, Christopher J Elkins, Sayuri D. Yapa, Julia B. Ling, John K. Eaton
    Abstract:

    Three-dimensional mean velocity and concentration fields have been measured for a water flow in a pressure side cutback trailing edge film cooling geometry consisting of rectangular film cooling slots separated by tapered lands. Three-component mean velocities were measured with conventional magnetic resonance velocimetry, while time-averaged concentration distributions were measured with a magnetic resonance concentration technique for flow at two Reynolds numbers ( Re ) differing by a factor of 2, three blowing ratios, and with and without an internal pin fin array in the coolant feed channel. The results show that the flows are essentially independent of Re for the regime tested in terms of the film cooling Surface Effectiveness, normalized velocity profiles, and normalized mean streamwise vorticity. Blowing ratio changes had a larger effect, with higher blowing ratios resulting in Surface Effectiveness improvements at downstream locations. The addition of a pin fin array within the slot feed channel made the spanwise distribution of coolant at the Surface more uniform. Results are compared with transonic experiments in air at realistic density ratios described by Holloway et al. (2002a) .

Julia Ling - One of the best experts on this subject based on the ideXlab platform.

  • the effect of land taper angle on trailing edge slot film cooling
    ASME Turbo Expo 2014: Turbine Technical Conference and Exposition, 2014
    Co-Authors: Julia Ling, Christopher J Elkins, John K. Eaton
    Abstract:

    Trailing edge slot film cooling is a widely used method of protecting the thin trailing edge of turbine blades from hot gas impingement. The structures that separate the slots, known as “lands,” come in a variety of configurations which can be broadly classified as either “tapered” or “straight.” This paper examines the effect of the land taper angle on the mixing of the coolant flow with the main flow by comparing three configurations: a case with straight lands, a previously reported case with slightly tapered lands, and a case with strongly tapered lands. In each case, the slot width and the land width at the plane of the slot exit are kept constant. For each configuration, the mean volumetric coolant concentration distribution and 3-component velocity field were measured using Magnetic Resonance Imaging techniques. It is shown that the land taper angle has a strong effect on the mean flow features and coolant Surface Effectiveness. Furthermore, the impact of the lands configuration on the flow field and concentration distribution is seen not just in the cutback region, but also in the wake of the blade.Copyright © 2014 by ASME

  • optimal turbulent schmidt number for rans modeling of trailing edge slot film cooling
    Journal of Engineering for Gas Turbines and Power-transactions of The Asme, 2014
    Co-Authors: Julia Ling, Christopher J Elkins, John K. Eaton
    Abstract:

    It has been previously demonstrated that Reynolds Averaged Navier Stokes (RANS) simulations do not accurately capture the mixing between the coolant flow and the main flow in trailing edge slot film cooling configurations. Most RANS simulations use a fixed turbulent Schmidt number of either 0.7 or 0.85 to determine the turbulent scalar flux, based on the values for canonical flows. This paper explores the extent to which RANS predictions can be improved by modifying the value of the turbulent Schmidt number. Experimental mean 3D velocity and coolant concentration data obtained using Magnetic Resonance Imaging techniques are used to evaluate the accuracy of RANS simulations. A range of turbulent Schmidt numbers from 0.05 to 1.05 is evaluated and the optimal turbulent Schmidt number for each case is determined using an integral error metric which accounts for the difference between RANS and experiment throughout a 3-dimensional region of interest. The resulting concentration distribution is compared in detail with the experimentally measured coolant concentration distribution to reveal where the fixed turbulent Schmidt number assumption fails. It is shown that the commonly used turbulent Schmidt number of 0.85 over-predicts the Surface Effectiveness in all cases, particularly when the k-omega SST model is employed, and that a lower value of the turbulent Schmidt number can improve predictions.Copyright © 2014 by ASME

Joh K Eato - One of the best experts on this subject based on the ideXlab platform.

  • experimental study of periodic free stream unsteadiness effects on discrete hole film cooling in two geometries
    ASME Turbo Expo 2018: Turbomachinery Technical Conference and Exposition, 2018
    Co-Authors: Daniel D Orup, Christophe J Elkins, Joh K Eato
    Abstract:

    Discrete hole film cooling is widely employed to protect turbine blades and vanes from hot combustion gases entering the high-pressure turbine stage. Accurate prediction of the heat transfer near film cooling holes is critical, and high-fidelity experimental data sets are needed for validation of new computational models. Relatively few studies have examined the effects of periodic main flow unsteadiness resulting from the interaction of turbine blades and vanes, with a particular lack of data for shaped hole configurations. Periodic unsteadiness was generated in the main flow over a laidback, fan-shaped cooling hole at a Strouhal number (St = fD/U) of 0.014 by an airfoil oscillating in pitch. Magnetic Resonance Imaging (MRI) with water as the working fluid was used to obtain full-field, phase-resolved velocity and scalar concentration data. Operating conditions consisted of a hole Reynolds number of 2900, channel Reynolds number of 25,000, and blowing ratio of unity. Both mean and phase-resolved data are compared to previous measurements for the same hole geometry with steady main flow. Under unsteady freestream conditions, the flow separation pattern inside the hole was observed to change from an asymmetric separation bubble to two symmetric bubbles. The periodic unsteadiness was characterized by alternating periods of slow main flow, which allowed the coolant to penetrate into the freestream along the centerplane, and fast, hole-impinging main flow, which deflected coolant towards the laidback wall and caused ejection of coolant from the hole away from the centerplane. Mean adiabatic Surface Effectiveness was reduced up to 23% inside the hole, while mean laterally-averaged Effectiveness outside the hole fell 28–36% over the entire measurement domain. A brief comparison to a round jet with and without unsteadiness is included; for the round jet, no disturbance was observed inside the hole, and some fluctuations directed coolant towards the wall, which increased mean film cooling Effectiveness. The combined velocity and concentration data for both cases are suitable for quantitative validation of CFD predictions for film cooling flows with periodic freestream unsteadiness.Copyright © 2018 by ASME

Daniel D Orup - One of the best experts on this subject based on the ideXlab platform.

  • experimental study of periodic free stream unsteadiness effects on discrete hole film cooling in two geometries
    ASME Turbo Expo 2018: Turbomachinery Technical Conference and Exposition, 2018
    Co-Authors: Daniel D Orup, Christophe J Elkins, Joh K Eato
    Abstract:

    Discrete hole film cooling is widely employed to protect turbine blades and vanes from hot combustion gases entering the high-pressure turbine stage. Accurate prediction of the heat transfer near film cooling holes is critical, and high-fidelity experimental data sets are needed for validation of new computational models. Relatively few studies have examined the effects of periodic main flow unsteadiness resulting from the interaction of turbine blades and vanes, with a particular lack of data for shaped hole configurations. Periodic unsteadiness was generated in the main flow over a laidback, fan-shaped cooling hole at a Strouhal number (St = fD/U) of 0.014 by an airfoil oscillating in pitch. Magnetic Resonance Imaging (MRI) with water as the working fluid was used to obtain full-field, phase-resolved velocity and scalar concentration data. Operating conditions consisted of a hole Reynolds number of 2900, channel Reynolds number of 25,000, and blowing ratio of unity. Both mean and phase-resolved data are compared to previous measurements for the same hole geometry with steady main flow. Under unsteady freestream conditions, the flow separation pattern inside the hole was observed to change from an asymmetric separation bubble to two symmetric bubbles. The periodic unsteadiness was characterized by alternating periods of slow main flow, which allowed the coolant to penetrate into the freestream along the centerplane, and fast, hole-impinging main flow, which deflected coolant towards the laidback wall and caused ejection of coolant from the hole away from the centerplane. Mean adiabatic Surface Effectiveness was reduced up to 23% inside the hole, while mean laterally-averaged Effectiveness outside the hole fell 28–36% over the entire measurement domain. A brief comparison to a round jet with and without unsteadiness is included; for the round jet, no disturbance was observed inside the hole, and some fluctuations directed coolant towards the wall, which increased mean film cooling Effectiveness. The combined velocity and concentration data for both cases are suitable for quantitative validation of CFD predictions for film cooling flows with periodic freestream unsteadiness.Copyright © 2018 by ASME