scholarly journals Measurements in Film Cooling Flows: Hole L/D and Turbulence Intensity Effects

1998 ◽  
Vol 120 (4) ◽  
pp. 791-798 ◽  
Author(s):  
S. W. Burd ◽  
R. W. Kaszeta ◽  
T. W. Simon
Keyword(s):  
Turbulence Intensity ◽  
Film Cooling ◽  
Stream Flow ◽  
Free Stream ◽  
Velocity Ratio ◽  
Density Ratio ◽  
Mean Velocity ◽  
Free Stream Turbulence ◽  
Cooling Hole ◽  
Film Cooling Holes

Hot-wire anemometry measurements of simulated film cooling are presented to document the influence of the free-stream turbulence intensity and film cooling hole length-to-diameter ratio on mean velocity and on turbulence intensity. Measurements are taken in the zone where the coolant and free-stream flows mix. Flow from one row of film cooling holes with a streamwise injection of 35 deg and no lateral injection and with a coolant-to-free-stream flow velocity ratio of 1.0 is investigated under free-stream turbulence levels of 0.5 and 12 percent. The coolant-to-free-stream density ratio is unity. Two length-to-diameter ratios for the film cooling holes, 2.3 and 7.0, are tested. The Measurements document that under low free-stream turbulence conditions pronounced differences exist in the flowfield between L/D= 7.0 and 2.3. The difference between L/D cases are less prominent at high free-stream turbulence intensities. Generally, Short-L/D injection results in “jetting” of the coolant farther into the free-stream flow and enhanced mixing. Other changes in the flowfield attributable to a rise in free-stream turbulence intensity to engine-representative conditions are documented.

Large-Scale Testing to Validate the Influence of External Crossflow on the Discharge Coefficients of Film Cooling Holes

2000 ◽  
Vol 123 (3) ◽  
pp. 593-600 ◽  
Author(s):  
D. A. Rowbury ◽  
M. L. G. Oldfield ◽  
G. D. Lock
Keyword(s):  
Film Cooling ◽  
Stream Flow ◽  
Large Scale ◽  
Discharge Coefficient ◽  
Static Pressure ◽  
Free Stream ◽  
Discharge Coefficients ◽  
Large Scale Testing ◽  
Cooling Hole ◽  
Film Cooling Holes

This paper discusses large-scale, low-speed experiments that explain unexpected flow-interaction phenomena witnessed during annular cascade studies into the influence of external crossflow on film cooling hole discharge coefficients. More specifically, the experiments throw light on the crossover phenomenon, where the presence of the external crossflow can, under certain circumstances, increase the discharge coefficient. This is contrary to most situations, where the external flow results in a decrease in discharge coefficient. The large-scale testing reported helps to explain this phenomenon through an increased understanding of the interaction between the emerging coolant jet and the free-stream flow. The crossover phenomenon came to light during an investigation into the influence of external crossflow on the discharge coefficients of nozzle guide vane film cooling holes. These experiments were performed in the Cold Heat Transfer Tunnel (CHTT), an annular blowdown cascade of film cooled vanes that models the three-dimensional external flow patterns found in modern aero-engines. (Rowbury et al., 1997, 1998). The variation in static pressure around the exit of film cooling holes under different flow conditions was investigated in the large-scale tests. The study centered on three holes whose geometries were based on those found in the leading edge region of the CHTT vanes, as the crossover phenomenon was witnessed for these rows during the initial testing. The experiments were carried out in a low-speed wind tunnel, with the tunnel free-stream flow velocity set to match the free-stream Reynolds number (based on the local radius of curvature) and the “coolant” flow velocity set to replicate the engine coolant-to-free-stream momentum flux ratio. It was found that the apparent enhancement of film cooling hole discharge coefficients with external crossflow was caused by a reduction in the static pressure around the hole exit, associated with the local acceleration of the free-stream around the emerging coolant jet. When these measured static pressures (rather than the free-stream static pressure) were used to calculate the discharge coefficient, the crossover effect was absent. The improved understanding of the crossover phenomenon and coolant-to-free-stream interactions that has been gained will be valuable in aiding the formulation of predictive discharge coefficient schemes.

Flow Measurements in Film Cooling Flows With Lateral Injection

1998 ◽  
Author(s):  
Richard W. Kaszeta ◽  
Terrence W. Simon ◽  
Rohit A. Oke ◽  
Steven W. Burd
Keyword(s):  
Turbulence Intensity ◽  
Film Cooling ◽  
Density Ratio ◽  
Intensity Level ◽  
Mean Velocity ◽  
Flow Measurements ◽  
Cooling Flows ◽  
General Flow ◽  
Flow Field Characteristics ◽  
Film Cooling Holes

Measurements of mean velocity and turbulence intensity are presented for the mixing region of a film cooling situation in which the coolant is laterally injected. Measurements are performed using triple-sensor anemometry so that all three velocity components are documented. Flow with one row of film cooling holes inclined 35° to the surface, with lateral injection (Φ = 90°), is documented. The freestream turbulence intensity level is 12%, and coolant-to-mainstream velocity ratios are 0.5 and 1.0 (the density ratio is unity). General flow field characteristics ore discussed and compared. Additional comparisons are made with similar measurements in a flow in which the injection is streamwise (Φ = 0°).

Rib Turbulator Effects on Crossflow-Fed Shaped Film Cooling Holes

2019 ◽  
Vol 141 (3) ◽  
Author(s):  
Dale W. Fox ◽  
Fraser B. Jones ◽  
John W. McClintic ◽  
David G. Bogard ◽  
Thomas E. Dyson ◽  
...  
Keyword(s):  
Film Cooling ◽  
Velocity Ratio ◽  
Cooling Effectiveness ◽  
Cooling Performance ◽  
Film Cooling Effectiveness ◽  
Smooth Channel ◽  
Cooling Hole ◽  
Film Cooling Holes ◽  
Inlet Position ◽  
The Impact

Most studies of turbine airfoil film cooling in laboratory test facilities have used relatively large plenums to feed flow into the coolant holes. However, a more realistic inlet condition for the film cooling holes is a relatively small channel. Previous studies have shown that the film cooling performance is significantly degraded when fed by perpendicular internal crossflow in a smooth channel. In this study, angled rib turbulators were installed in two geometric configurations inside the internal crossflow channel, at 45 deg and 135 deg, to assess the impact on film cooling effectiveness. Film cooling hole inlets were positioned in both prerib and postrib locations to test the effect of hole inlet position on film cooling performance. A test was performed independently varying channel velocity ratio and jet to mainstream velocity ratio. These results were compared to the film cooling performance of previously measured shaped holes fed by a smooth internal channel. The film cooling hole discharge coefficients and channel friction factors were also measured for both rib configurations with varying channel and inlet velocity ratios. Spatially averaged film cooling effectiveness is largely similar to the holes fed by the smooth internal crossflow channel, but hole-to-hole variation due to inlet position was observed.

scholarly journals Entrance Effects on Diffused Film-Cooling Holes

1998 ◽  
Author(s):  
A. Kohli ◽  
K. A. Thole
Keyword(s):  
Reynolds Number ◽  
Film Cooling ◽  
Gas Turbines ◽  
High Performance ◽  
Computational Study ◽  
Density Ratio ◽  
Reynolds Numbers ◽  
Supply Channel ◽  
Cooling Hole ◽  
Film Cooling Holes

Film-cooling is a widely used method of prolonging blade life in high performance gas turbines and is implemented by injecting cold air through discrete holes on the blade surface. Most experimental research on film-cooling has been performed using round holes supplied by a stagnant plenum. This can be quite different from the actual turbine blade conditions in that a crossflow may be present whereby the internal channel Reynolds number could be as high as 90,000. This computational study uses a film-cooling hole that is inclined at 35° with respect to the mainstream and is diffused at the hole exit by 15°. An engine representative jet-to-mainstream density ratio of two was simulated. The test matrix consisted of fourteen different cases that were simulated for the two different blowing ratios in which the following effects were investigated: a) the effect of the orientation of the coolant supply channel relative to the cooling hole, b) the effect of the channel Reynolds number, and c) the effect of the metering length of the cooling hole. Results showed that the orientation of the coolant supply had a large effect whereby the worst orientation, in terms of a reduced adiabatic effectiveness, was predicted when the channel supplying the cooling hole was perpendicular to the mainstream. For this particular orientation, higher laterally averaged effectiveness occurred at lower channel Reynolds numbers and with the hole having a short metering length.

The Influence of Coolant Supply Geometry on Film Coolant Exit Flow and Surface Adiabatic Effectiveness

1997 ◽  
Author(s):  
Steven W. Burd ◽  
Terrence W. Simon
Keyword(s):  
Turbulence Intensity ◽  
Film Cooling ◽  
Velocity Ratio ◽  
Turbine Engines ◽  
Freestream Velocity ◽  
Cooling Flow ◽  
Adiabatic Effectiveness ◽  
Density Ratios ◽  
Film Cooling Holes ◽  
Counter Current

Experimental hot-wire anemometry and thermocouple measurements are taken to document the sensitivity which film cooling performance has to the hole length and the geometry of the plenum which supplies cooling flow to the holes. This sensitivity is described in terms of the effects these geometric features have on hole-exit velocity and turbulence intensity distributions and on adiabatic effectiveness values on the surface downstream. These measurements were taken under high freestream turbulence intensity (12%) conditions, representative of operating gas turbine engines. Coolant is supplied to the film cooling holes by means of (1) an unrestricted plenum, (2) a plenum which restricts the flow approaching the holes, forcing it to flow co-current with the freestream, and (3) a plenum which forces the flow to approach the holes counter-current with the freestream. Short-hole (L/D = 2.3) and long-hole (L/D = 7.0) comparisons are made. The geometry has a single row of film cooling holes with 35°-inclined streamwise injection. The film cooling flow is supplied at the same temperature as that of the freestream for hole-exit measurements and 10°C above the freestream temperature for adiabatic effectiveness measurements, yielding density ratios in the range 0.96–1.0. Two coolant-to-freestream velocity ratios, 0.5 and 1.0, are investigated. The results document the effects of (1) supply plenum geometry, (2) velocity ratio, and (3) hole L/D.

Film Cooling Measurements for a Laidback Fan-Shaped Hole: Effect of Coolant Crossflow on Cooling Effectiveness and Heat Transfer

2019 ◽  
Vol 141 (4) ◽  
Author(s):  
Marc Fraas ◽  
Tobias Glasenapp ◽  
Achmed Schulz ◽  
Hans-Jörg Bauer
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Film Cooling ◽  
Gas Flow ◽  
Density Ratio ◽  
Coolant Flow ◽  
Cooling Effectiveness ◽  
Film Cooling Effectiveness ◽  
Cooling Hole ◽  
Film Cooling Holes

Internal coolant passages of gas turbine vanes and blades have various orientations relative to the external hot gas flow. As a consequence, the inflow of film cooling holes varies as well. To further identify the influencing parameters of film cooling under varying inflow conditions, the present paper provides detailed experimental data. The generic study is performed in a novel test rig, which enables compliance with all relevant similarity parameters including density ratio. Film cooling effectiveness as well as heat transfer of a 10–10–10 deg laidback fan-shaped cooling hole is discussed. Data are processed and presented over 50 hole diameters downstream of the cooling hole exit. First, the parallel coolant flow setup is discussed. Subsequently, it is compared to a perpendicular coolant flow setup at a moderate coolant channel Reynolds number. For the perpendicular coolant flow, asymmetric flow separation in the diffuser occurs and leads to a reduction of film cooling effectiveness. For a higher coolant channel Reynolds number and perpendicular coolant flow, asymmetry increases and cooling effectiveness is further decreased. An increase in blowing ratio does not lead to a significant increase in cooling effectiveness. For all cases investigated, heat transfer augmentation due to film cooling is observed. Heat transfer is highest in the near-hole region and decreases further downstream. Results prove that coolant flow orientation has a severe impact on both parameters.

Flowfield Measurements for Film-Cooling Holes With Expanded Exits

1998 ◽  
Vol 120 (2) ◽  
pp. 327-336 ◽  
Author(s):  
K. Thole ◽  
M. Gritsch ◽  
A. Schulz ◽  
S. Wittig
Keyword(s):  
Mach Number ◽  
Film Cooling ◽  
Turbine Blades ◽  
Density Ratio ◽  
Round Hole ◽  
Turbulence Level ◽  
Jet In Crossflow ◽  
Expansion Angle ◽  
Cooling Hole ◽  
Film Cooling Holes

One viable option to improve cooling methods used for gas turbine blades is to optimize the geometry of the film-cooling hole. To optimize that geometry, effects of the hole geometry on the complex jet-in-crossflow interaction need to be understood. This paper presents a comparison of detailed flowfield measurements for three different single, scaled-up hole geometries, all at a blowing ratio and density ratio of unity. The hole geometries include a round hole, a hole with a laterally expanded exit, and a hole with a forward-laterally expanded exit. In addition to the flowfield measurements for expanded cooling hole geometries being unique to the literature, the testing facility used for these measurements was also unique in that both the external mainstream Mach number (Ma∞ = 0.25) and internal coolant supply Mach number (Mac = 0.3) were nearly matched. Results show that by expanding the exit of the cooling holes, both the penetration of the cooling jet and the intense shear regions are significantly reduced relative to a round hole. Although the peak turbulence level for all three hole geometries was nominally the same, the source of that turbulence was different. The peak turbulence level for both expanded holes was located at the exit of the cooling hole resulting from the expansion angle being too large. The peak turbulence level for the round hole was located downstream of the hole exit where the velocity gradients were very large.

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.

Enhanced Film Cooling Effectiveness With Surface Trenches

2013 ◽  
Author(s):  
K. Vighneswara Rao ◽  
Jong S. Liu ◽  
Daniel C. Crites ◽  
Luis A. Tapia ◽  
Malak F. Malak ◽  
...  
Keyword(s):  
Film Cooling ◽  
Density Ratio ◽  
Operating Conditions ◽  
Airfoil Surface ◽  
Cooling Effectiveness ◽  
Film Cooling Effectiveness ◽  
Ansys Cfx ◽  
Cooling Hole ◽  
Computational Fluid Dynamics Cfd ◽  
Film Cooling Holes

In this study, cylindrical and fan shaped film cooling holes are evaluated on the blade surface numerically, using the Computational Fluid Dynamics (CFD) tool ANSYS-CFX, with the objective of improving cooling effectiveness by understanding the flow pattern at the cooling hole exit. The coolant flow rates are adjusted for blowing ratios of 0.5, 1.0 & 1.5 (momentum flux ratios of 0.125, 0.5 & 1.125 respectively). The density ratio is maintained at 2.0. New shaped holes viz. straight, concave and convex trench holes are introduced and are evaluated under similar operating conditions. Results are presented in terms of surface temperatures and adiabatic effectiveness at three different blowing ratios for the different film cooling hole shapes analyzed. Comparison is made with reference to the fan shaped film cooling hole to bring out relative merits of different shapes. The new trench holes improved the film cooling effectiveness by allowing more residence time for coolant to spread laterally while directing smoothly onto the airfoil surface. While convex trench improved the centre-line effectiveness, straight trench improved the laterally-averaged and overall effectiveness at all blowing ratios. Concave trench improved the effectiveness at blowing ratios 0.5 and 1.0.

Effect of High Freestream Turbulence on Flowfields of Shaped Film Cooling Holes

2015 ◽  
Author(s):  
Robert P. Schroeder ◽  
Karen A. Thole
Keyword(s):  
Gas Turbine ◽  
Turbulence Intensity ◽  
Film Cooling ◽  
Density Ratio ◽  
Vortex Pair ◽  
Lateral Spreading ◽  
Freestream Turbulence ◽  
Blowing Ratio ◽  
Turbine Airfoils ◽  
Film Cooling Holes

Shaped film cooling holes have become a standard geometry for protecting gas turbine components. Few studies, however, have reported flowfield measurements for moderately-expanded shaped holes and even fewer have reported on the effects of high freestream turbulence intensity relevant to gas turbine airfoils. This study presents detailed flowfield and adiabatic effectiveness measurements for a shaped hole at freestream turbulence intensities of 0.5% and 13%. Test conditions included blowing ratios of 1.5 and 3 at a density ratio of 1.5. Measured flowfields revealed a counter-rotating vortex pair and high jet penetration into the mainstream at the blowing ratio of 3. Elevated freestream turbulence had a minimal effect on mean velocities and rather acted by increasing turbulence intensity around the coolant jet, resulting in increased lateral spreading of coolant.

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