Thermal Field Measurements for a Shaped Hole at Low and High Freestream Turbulence Intensity

2016 ◽  
Author(s):  
Robert P. Schroeder ◽  
Karen A. Thole
Keyword(s):  
Turbulence Intensity ◽  
Gas Turbines ◽  
Thermal Field ◽  
Vertical Direction ◽  
Field Measurements ◽  
Superior Performance ◽  
Turbulent Shear ◽  
Freestream Turbulence ◽  
Thermal Fields ◽  
Shaped Hole

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.

Thermal Field Measurements for a Shaped Hole at Low and High Freestream Turbulence Intensity

2016 ◽  
Vol 139 (2) ◽  
Author(s):  
Robert P. Schroeder ◽  
Karen A. Thole
Keyword(s):  
Turbulence Intensity ◽  
Gas Turbines ◽  
Thermal Field ◽  
Vertical Direction ◽  
Field Measurements ◽  
Superior Performance ◽  
Turbulent Shear ◽  
Freestream Turbulence ◽  
Thermal Fields ◽  
Shaped Hole

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.

Sweeping Jet Film Cooling at High Blowing Ratio on a Turbine Vane

2019 ◽  
Author(s):  
Mohammad A. Hossain ◽  
Ali Ameri ◽  
James W. Gregory ◽  
Jeffrey P. Bons
Keyword(s):  
Boundary Layer ◽  
Film Cooling ◽  
Thermal Field ◽  
Guide Vane ◽  
Freestream Turbulence ◽  
Suction Surface ◽  
Blowing Ratio ◽  
Shaped Hole ◽  
D 12 ◽  
Nozzle Guide

Abstract Experimental and numerical investigations were conducted to study the effects of high blowing ratios and high freestream turbulence on sweeping jet film cooling. Experiments were conducted on a nozzle guide vane suction surface in a low-speed linear cascade. Experiments were performed at blowing ratios of 0.5–3.5 and freestream turbulence of 0.6% and 14.3%. Infrared thermography was used to estimate the adiabatic cooling effectiveness. Thermal field and boundary layer measurement were conducted at a cross-plane (x/D = 12) downstream of the hole exit. Results were compared with a baseline 777-shaped hole and showed that sweeping jet hole has a better cooling performance at high blowing ratios. The Thermal field data revealed that the coolant separates from the surface at high blowing ratios for the 777-shaped hole while the coolant remains attached for the sweeping jet hole. Boundary layer measurement further confirmed that due to the sweeping action of the jet, the jet momentum of the sweeping jet hole is much lower than that of a 777-shaped hole. Thus the coolant remains closer to the wall even at high blowing ratios. Large Eddy Simulations (LES) were performed for both sweeping jet and the 777-shaped hole to evaluate the interaction between the coolant and the freestream at the near hole regions. Results showed that 777-shaped hole has a strong jetting action at high blowing ratio that originates inside the hole breakout edges thus causing the jet to blow off from the surface. In contrast, the sweeping jet hole does not show this behavior due to its internal geometry and the sweeping action of the jet.

Effect of Freestream Turbulence Intensity on Film Cooling Jet Structure and Surface Effectiveness Using PIV and PSP

2011 ◽  
Vol 133 (4) ◽  
Author(s):  
Lesley M. Wright ◽  
Stephen T. McClain ◽  
Michael D. Clemenson
Keyword(s):  
Turbulence Intensity ◽  
Film Cooling ◽  
Field Measurements ◽  
Freestream Turbulence ◽  
Mean Velocity ◽  
Cooling Effectiveness ◽  
Piv Measurements ◽  
Film Cooling Effectiveness ◽  
Film Cooling Holes ◽  
Jet Structure

An experimental investigation of film cooling jet structure using two-dimensional particle image velocimetry (PIV) has been completed for cylindrical, simple angle (θ=35 deg) film cooling holes. The PIV measurements are coupled with detailed film cooling effectiveness distributions on the flat plate obtained using a steady state, pressure sensitive paint (PSP) technique. Both the flow and surface measurements were performed in a low speed wind tunnel where the freestream turbulence intensity was varied from 1.2% to 12.5%. With this traditional film cooling configuration, the blowing ratio was varied from 0.5 to 1.5 to compare the jet structure of relatively low and high momentum cooling flows. Velocity maps of the coolant flow (in the streamwise direction) are obtained on three planes spanning a single hole: centerline, 0.25D, and 0.5D (outer edge of the film cooling hole). From the seeded jets, time averaged, mean velocity distributions of the film cooling jets are obtained near the cooled surface. In addition, turbulent fluctuations are obtained for each flow condition. Combining the detailed flow field measurements obtained using PIV (both instantaneous and time averaged) with detailed film cooling effectiveness distributions on the surface (PSP) provides a more complete view of the coolant jet-mainstream flow interaction. Near the edge of the film cooling holes, the turbulent mixing increases, and as a result the film cooling effectiveness decreases. Furthermore, the PIV measurements show the increased mixing of the coolant jet with the mainstream at the elevated freestream turbulence level resulting in a reduction in the jet to effectively protect the film cooled surface.

ADIABATIC EFFECTIVENESS AND THERMAL FIELD MEASUREMENTS OF A SHAPED HOLE IN THE SHOWERHEAD OF A MODEL TURBINE BLADE

2021 ◽  
pp. 1-37
Author(s):  
Jacob D. Moore ◽  
Matthew Horner ◽  
David G. Bogard
Keyword(s):  
Turbine Blade ◽  
Thermal Field ◽  
Leading Edge ◽  
Field Measurements ◽  
Injection Rate ◽  
Edge Region ◽  
Test Environment ◽  
Coolant Injection ◽  
Shaped Hole ◽  
Adiabatic Effectiveness

Abstract Few published studies incorporating shaped hole designs in the leading-edge region, or showerhead, of turbine airfoils have been performed; but among them is the indication that shaped holes may offer an improvement in coolant performance compared to cylindrical holes. A shaped hole was designed with the goal of high performance in the showerhead. The performance and physical behavior of this shaped hole design was studied in comparison to a traditional cylindrical hole design in a series of experiments. The geometries were built into the leading edge of a scaled-up turbine blade model for testing in a low-speed simulated linear cascade. To accomplish an engine-representative test environment, a nominally 5% approach turbulence level was used for this study. Adiabatic effectiveness as a function of coolant injection rate was measured for the two designs using infrared thermography. In addition, off-the-wall thermal field measurements were performed for each hole geometry in the leading-edge region. It was found that the shaped hole offered ~20-100% higher performance in terms of adiabatic effectiveness depending on the coolant injection rate. The thermal field measurements suggested that this was due to the better attachment of the jets exiting the shaped holes, the momenta of which were effectively reduced by the diffusers.

Effect of Freestream Turbulence Intensity on Film Cooling Jet Structure and Surface Effectiveness Using PIV and PSP

2010 ◽  
Author(s):  
Lesley M. Wright ◽  
Stephen T. McClain ◽  
Michael D. Clemenson
Keyword(s):  
Turbulence Intensity ◽  
Film Cooling ◽  
Field Measurements ◽  
Freestream Turbulence ◽  
Mean Velocity ◽  
Cooling Effectiveness ◽  
Piv Measurements ◽  
Film Cooling Effectiveness ◽  
Film Cooling Holes ◽  
Jet Structure

An experimental investigation of film cooling jet structure using two-dimensional, particle image velocimetry (PIV) has been completed for cylindrical, simple angle (θ = 35°) film cooling holes. The PIV measurements are coupled with detailed film cooling effectiveness distributions on the flat plate obtained using a steady state, pressure sensitive paint (PSP) technique. Both the flow and surface measurements were performed in a low speed wind tunnel where the freestream turbulence intensity was varied from 1.2% to 12.5%. With this traditional film cooling configuration, the blowing ratio was varied from 0.5–1.5 to compare the jet structure of relatively low and high momentum cooling flows. Velocity maps of the coolant flow (in the streamwise direction) are obtained on three planes spanning a single hole: centerline, 0.25D, and 0.5D (outer edge of the film cooling hole). From the seeded jets, time averaged, mean velocity distributions of the film cooling jets are obtained near the cooled surface. In addition, turbulent fluctuations are obtained for each flow condition. Combining the detailed flow field measurements obtained using PIV (both instantaneous and time averaged) with detailed film cooling effectiveness distributions on the surface (PSP), provides a more complete view of the coolant jet–mainstream flow interaction. Near the edge of the film cooling holes, the turbulent mixing increases, and as a result the film cooling effectiveness decreases. Furthermore, the PIV measurements show the increased mixing of the coolant jet with the mainstream at the elevated freestream turbulence level resulting in a reduction of the jet to effectively protect the film cooled surface.

Weakly sheared turbulent flows generated by multiscale inhomogeneous grids

2018 ◽  
Vol 848 ◽  
pp. 788-820 ◽  
Author(s):  
Shaokai Zheng ◽  
P. J. K. Bruce ◽  
J. M. R. Graham ◽  
J. C. Vassilicos
Keyword(s):  
Velocity Profile ◽  
Turbulence Intensity ◽  
Shear Flows ◽  
Vertical Direction ◽  
Turbulent Shear ◽  
Incoming Flow ◽  
Mean Velocity ◽  
Free Stream Turbulence ◽  
The Mean ◽  
Vertical Bars

A group of three multiscale inhomogeneous grids have been tested to generate different types of turbulent shear flows with different mean shear rate and turbulence intensity profiles. Cross hot-wire measurements were taken in a wind tunnel with Reynolds number$Re_{D}$of 6000–20 000, based on the width of the vertical bars of the grid and the incoming flow velocity. The effect of local drag coefficient$C_{D}$on the mean velocity profile is discussed first, and then by modifying the vertical bars to obtain a uniform aspect ratio the mean velocity profile is shown to be predictable using the local blockage ratio profile. It is also shown that, at a streamwise location$x=x_{m}$, the turbulence intensity profile along the vertical direction$u^{\prime }(y)$scales with the wake interaction length$x_{\ast ,n}^{peak}=0.21g_{n}^{2}/(\unicode[STIX]{x1D6FC}C_{D}w_{n})$($\unicode[STIX]{x1D6FC}$is a constant characterizing the incoming flow condition, and$g_{n}$,$w_{n}$are the gap and width of the vertical bars, respectively, at layer$n$) such that$(u^{\prime }/U_{n})^{2}\unicode[STIX]{x1D6FD}^{2}(C_{D}w_{n}/x_{\ast ,n}^{peak})^{-1}\sim (x_{m}/x_{\ast ,n}^{peak})^{b}$, where$\unicode[STIX]{x1D6FD}$is a constant determined by the free-stream turbulence level,$U_{n}$is the local mean velocity and$b$is a dimensionless power law constant. A general framework of grid design method based on these scalings is proposed and discussed. From the evolution of the shear stress coefficient$\unicode[STIX]{x1D70C}(x)$, integral length scale$L(x)$and the dissipation coefficient$C_{\unicode[STIX]{x1D716}}(x)$, a simple turbulent kinetic energy model is proposed that describes the evolution of our grid generated turbulence field using one centreline measurement and one vertical profile of$u^{\prime }(y)$at the beginning of the evolution. The results calculated from our model agree well with our measurements in the streamwise extent up to$x/H\approx 2.5$, where$H$is the height of the grid, suggesting that it might be possible to design some shear flows with desired mean velocity and turbulence intensity profiles by designing the geometry of a passive grid.

Sweeping Jet Film Cooling at High Blowing Ratio on a Turbine Vane

2020 ◽  
Vol 142 (12) ◽  
Author(s):  
Mohammad A. Hossain ◽  
Ali Ameri ◽  
James W. Gregory ◽  
Jeffrey P. Bons
Keyword(s):  
Boundary Layer ◽  
Film Cooling ◽  
Thermal Field ◽  
Guide Vane ◽  
Freestream Turbulence ◽  
Suction Surface ◽  
Cooling Effectiveness ◽  
Blowing Ratio ◽  
Shaped Hole ◽  
D 12

Abstract Experimental and numerical investigations were performed to study the effects of high blowing ratios and high freestream turbulence on sweeping jet film cooling. Experiments were conducted on a nozzle guide vane suction surface in a low-speed linear cascade at a range of blowing ratios of 0.5–3.5 and freestream turbulence of 0.6% and 14.3%. Infrared thermography was used to estimate the adiabatic cooling effectiveness. Thermal field and boundary layer measurements were conducted at a cross-plane at x/D = 12 downstream of the hole exit. Results were compared with a baseline 777-shaped hole and showed that the sweeping jet hole has improved cooling effectiveness at high blowing ratios (M > 1). The thermal field data revealed that the coolant separates from the surface at high blowing ratios for the 777-shaped hole while the coolant remains attached for the sweeping jet hole. Boundary layer measurements further confirmed that due to the sweeping motion of the jet, the effective jet momentum of the sweeping jet hole remains much lower than that of a 777-shaped hole. Thus, the coolant remains closer to the wall even at high blowing ratios. Large Eddy simulations (LES) were performed for both the sweeping jet and 777-shaped hole to evaluate the interaction between the coolant jet and the freestream in the near hole regions. Results showed that 777-shaped hole has a strong jetting at high blowing ratio that originates inside the hole breakout edges thus causing the jet to blow-off from the surface. In contrast, the sweeping jet does not show this behavior due to its internal geometry and flapping motion of the jet.

Adiabatic Effectiveness and Thermal Field Measurements of a Shaped Hole in the Showerhead of a Model Turbine Blade

2020 ◽  
Author(s):  
Jacob D. Moore ◽  
Matthew J. Horner ◽  
David G. Bogard
Keyword(s):  
Turbine Blade ◽  
Thermal Field ◽  
Leading Edge ◽  
Field Measurements ◽  
Injection Rate ◽  
Edge Region ◽  
Test Environment ◽  
Coolant Injection ◽  
Shaped Hole ◽  
Adiabatic Effectiveness

Abstract Few published studies incorporating shaped hole designs in the leading-edge region, or showerhead, of turbine airfoils have been performed; but among them is the indication that shaped holes may offer an improvement in coolant performance compared to cylindrical holes. A shaped hole was designed with the goal of high performance in the showerhead. The performance and physical behavior of this shaped hole design was studied in comparison to a traditional cylindrical hole design in a series of experiments. The geometries were built into the leading edge of a scaled-up turbine blade model for testing in a low-speed simulated linear cascade. To accomplish an engine-representative test environment, a nominally 5% approach turbulence level was used for this study. Adiabatic effectiveness as a function of coolant injection rate was measured for the two designs using infrared thermography. In addition, off-the-wall thermal field measurements were performed for each hole geometry in the leading-edge region. It was found that the shaped hole offered ∼20–100% higher performance in terms of adiabatic effectiveness depending on the coolant injection rate. The thermal field measurements suggested that this was due to the better attachment of the jets exiting the shaped holes, the momenta of which were effectively reduced by the diffusers.

scholarly journals Flow and Thermal Field Measurements in a Combustor Simulator Relevant to a Gas Turbine Aero-Engine

2003 ◽  
Author(s):  
S. S. Vakil ◽  
K. A. Thole
Keyword(s):  
Gas Turbine ◽  
High Performance ◽  
Large Scale ◽  
Thermal Field ◽  
Field Measurements ◽  
Turbine Engines ◽  
Laser Doppler Velocimeter ◽  
High Momentum ◽  
Thermal Fields ◽  
Aero Engine

The current demands for high performance gas turbine engines can be reached by raising combustion temperatures to increase power output. Predicting the performance of a combustor is quite challenging, particularly the turbulence levels that are generated as a result of injection from high momentum dilution jets. Prior to predicting reactions in a combustor, it is imperative that these turbulence levels can be accurately predicted. The measurements presented in this paper are of flow and thermal fields produced in a large-scale combustor simulator, which is representative of an aero-engine. Three-component laser Doppler velocimeter measurements were made to quantify the velocity field while a rake of thermocouples was used to quantify the thermal field. The results indicate large penetration depths for the high momentum dilution jets, which result in a highly turbulent flow field. As these dilution jets interact with the mainstream flow, kidney shaped thermal fields result due to counter-rotating vortices that develop.

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