Film Cooling Effectiveness Improvements Using a Non-Diffusing Oval Hole

2015 ◽  
Author(s):  
Emin Issakhanian ◽  
Christopher J. Elkins ◽  
John K. Eaton
Keyword(s):  
Film Cooling ◽  
Vortex Pair ◽  
Round Hole ◽  
Blade Surface ◽  
Cooling Effectiveness ◽  
Film Cooling Effectiveness ◽  
Cooling Hole ◽  
Counter Rotating Vortex Pair ◽  
Shaped Hole ◽  
Film Cooling Holes

The need for improvements in film cooling effectiveness over traditional cylindrical film cooling holes has led to varied shaped hole and sister hole designs of increasing complexity. This paper presents a simpler shaped-hole design which shows improved film cooling effectiveness over both cylindrical holes and diffusing fan-shaped holes without the geometric complexity of the latter. Magnetic resonance imaging measurement techniques are used to reveal the coupled 3D velocity and coolant mixing from film cooling holes which are of a constant oval cross-section as opposed to round. The oval shaped hole yielded an area-averaged adiabatic effectiveness twice that of the diffusing fan-shaped hole tested. Three component mean velocity measurements within the channel and cooling hole showed the flow features and vorticity fields which explain the improved performance of the oval shaped hole. As compared to the round hole, the oval hole leads to a more complex vorticity field which reduces the strength of the main counter-rotating vortex pair. The counter-rotating vortex pair acts to lift the coolant away from the turbine blade surface and thus strongly reduces the film cooling effectiveness. The weaker vortices allow coolant to stay closer to the blade surface and to remain relatively unmixed with the main flow over a longer distance. Thus, the oval-shaped film cooling hole provides a simpler solution for improving film cooling effectiveness beyond circular hole and diffusing hole designs.

Film Cooling Effectiveness Improvements Using a Nondiffusing Oval Hole

2015 ◽  
Vol 138 (4) ◽  
Author(s):  
Emin Issakhanian ◽  
Christopher J. Elkins ◽  
John K. Eaton
Keyword(s):  
Film Cooling ◽  
Measurement Techniques ◽  
Round Hole ◽  
Blade Surface ◽  
Mean Velocity ◽  
Cooling Effectiveness ◽  
Film Cooling Effectiveness ◽  
Cooling Hole ◽  
Shaped Hole ◽  
Film Cooling Holes

The need for improvements in film cooling effectiveness over traditional cylindrical film cooling holes has led to varied shaped hole and sister hole designs of increasing complexity. This paper presents a simpler shaped hole design which shows improved film cooling effectiveness over both cylindrical holes and diffusing fan-shaped holes without the geometric complexity of the latter. Magnetic resonance imaging measurement techniques are used to reveal the coupled 3D velocity and coolant mixing from film cooling holes which are of a constant oval cross section as opposed to round. The oval-shaped hole yielded an area-averaged adiabatic effectiveness twice that of the diffusing fan-shaped hole tested. Three component mean velocity measurements within the channel and cooling hole showed the flow features and vorticity fields which explain the improved performance of the oval-shaped hole. As compared to the round hole, the oval hole leads to a more complex vorticity field, which reduces the strength of the main counter-rotating vortex pair (CVP). The CVP acts to lift the coolant away from the turbine blade surface, and thus strongly reduces the film cooling effectiveness. The weaker vortices allow the coolant to stay closer to the blade surface and to remain relatively unmixed with the main flow over a longer distance. Thus, the oval-shaped film cooling hole provides a simpler solution for improving film cooling effectiveness beyond circular hole and diffusing hole designs.

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.

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.

Film Cooling of Cylindrical Hole With a Downstream Short Crescent-Shaped Block

2013 ◽  
Vol 135 (3) ◽  
Author(s):  
Baitao An ◽  
Jianjun Liu ◽  
Chao Zhang ◽  
Sijing Zhou
Keyword(s):  
Film Cooling ◽  
Density Ratio ◽  
Vortex Pair ◽  
Cylindrical Hole ◽  
Test Case ◽  
Main Body ◽  
Lateral Direction ◽  
Cooling Effectiveness ◽  
Film Cooling Effectiveness ◽  
Cooling Hole

This paper presents a method to improve the film-cooling effectiveness of cylindrical holes. A short crescent-shaped block is placed at the downstream of a cylindrical cooling hole. The block shape is defined by a number of geometric parameters including block height, length and width, etc. The single row hole on a flat plate with inclination angle of 30 deg, pitch ratio of 3, and length-diameter ratio of 6.25 was chosen as the baseline test case. Film-cooling effectiveness for the cylindrical hole with or without the downstream short crescent-shaped block was measured by using the pressure sensitive paint (PSP) technique. The density ratio of coolant (argon) to mainstream air is 1.38. The blowing ratios vary from 0.5 to 1.25. The results showed that the lateral averaged cooling effectiveness is increased remarkably when the downstream block is present. The downstream short block allows the main body of the coolant jet to pass over the block top and to form a new down-wash vortex pair, which increases the coolant spread in the lateral direction. The effects of each geometrical parameter of the block on the film-cooling effectiveness were studied in detail.

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.

Turbine Blade Platform Film Cooling With Typical Stator-Rotor Purge Flow and Discrete-Hole Film Cooling

2009 ◽  
Vol 131 (4) ◽  
Author(s):  
Zhihong Gao ◽  
Diganta Narzary ◽  
Je-Chin Han
Keyword(s):  
Film Cooling ◽  
Pressure Loss ◽  
Total Pressure ◽  
Total Pressure Loss ◽  
Cooling Effectiveness ◽  
Film Cooling Effectiveness ◽  
Cooling Hole ◽  
Purge Flow ◽  
Cylindrical Holes ◽  
Film Cooling Holes

This paper is focused on the effect of film-hole configurations on platform film cooling. The platform is cooled by purge flow from a simulated stator-rotor seal combined with discrete-hole film cooling within the blade passage. The cylindrical holes and laidback fan-shaped holes are assessed in terms of film-cooling effectiveness and total pressure loss. Lined up with the freestream streamwise direction, the film holes are arranged on the platform with two different layouts. In one layout, the film-cooling holes are divided into two rows and more concentrated on the pressure side of the passage. In the other layout, the film-cooling holes are divided into four rows and loosely distributed on the platform. Four film-cooling hole configurations are investigated totally. Testing was done in a five-blade cascade with medium high Mach number condition (0.27 and 0.44 at the inlet and the exit, respectively). The detailed film-cooling effectiveness distributions on the platform were obtained using pressure sensitive paint technique. Results show that the combined cooling scheme (slot purge flow cooling combined with discrete-hole film cooling) is able to provide full film coverage on the platform. The shaped holes present higher film-cooling effectiveness and wider film coverage than the cylindrical holes, particularly at higher blowing ratios. The hole layout affects the local film-cooling effectiveness. The shaped holes also show the advantage over the cylindrical holes with lower total pressure loss.

Turbine Blade Platform Film Cooling With Typical Stator-Rotor Purge Flow and Discrete-Hole Film Cooling

2008 ◽  
Author(s):  
Zhihong Gao ◽  
Diganta Narzary ◽  
Je-Chin Han
Keyword(s):  
Film Cooling ◽  
Pressure Loss ◽  
Total Pressure ◽  
Total Pressure Loss ◽  
Cooling Effectiveness ◽  
Film Cooling Effectiveness ◽  
Cooling Hole ◽  
Purge Flow ◽  
Cylindrical Holes ◽  
Film Cooling Holes

This paper is focused on the effect of film hole configurations on platform film cooling. The platform is cooled by purge flow from a simulated stator-rotor seal combined with discrete-hole film cooling within the blade passage. The cylindrical holes and laidback fan-shaped holes are assessed in terms of film cooling effectiveness and total pressure loss. Lined up with the freestream streamwise direction, the film holes are arranged on the platform with two different layouts. In one layout, the film cooling holes are divided into two rows and more concentrated on the pressure side of the passage. In the other layout, the film cooling holes are divided into four rows and loosely distributed on the platform. Four film cooling hole configurations are investigated totally. Testing was done in a five-blade cascade with medium high Mach number condition (0.27 and 0.44 at the inlet and the exit, respectively). The detailed film cooling effectiveness distributions on the platform was obtained using pressure sensitive paint (PSP) technique. Results show that the combined cooling scheme (slot purge flow cooling combined with discrete hole film cooling) is able to provide full film coverage on the platform. The shaped holes present higher film cooling effectiveness and wider film coverage than the cylindrical holes, particularly at higher blowing ratios. The hole layout affects the local film cooling effectiveness. The shaped holes also show the advantage over the cylindrical holes with lower total pressure loss.

Enhanced Cooling Effectiveness in Full-Coverage Film Cooling System With Impingement Jets

2008 ◽  
Author(s):  
Sang Hyun Oh ◽  
Dong Hyun Lee ◽  
Kyung Min Kim ◽  
Moon Young Kim ◽  
Hyung Hee Cho
Keyword(s):  
Film Cooling ◽  
Cooling System ◽  
Hole Diameter ◽  
Cooling Effectiveness ◽  
Cooling Plate ◽  
Film Cooling Effectiveness ◽  
Impingement Jet ◽  
Full Coverage ◽  
Cooling Hole ◽  
Film Cooling Holes

An experimental investigation is conducted on the cooling effectiveness of full-coverage film cooled wall with impingement jets. Film cooling plate is made of stainless steel, thus the adiabatic film cooling effectiveness and the cooling effect of impingement jet underneath the film cooling plate are comprised in the cooling effectiveness. Infra-red camera is used to measure the temperature of film cooled surfaces. Experiments are conducted with different film cooling hole angles, such as 35° and 90°. Diameters of both film cooling holes and impinging jet holes are 5 mm. The jet Reynolds number base on the hole diameter (Red) ranges from 3,000 to 5,000 and equivalent blowing ratios (M) varies from 0.3 to 0.5, respectively. The distance between the injection plate and the film cooling plate is 1, 3 and 5 times of the hole diameter. The streamwise and spanwise hole spacing to the hole diameter ratio (p/d) are 3 for both the film cooling hole plate and the impingement jet hole plate. The 35° angled film cooling hole arrangement shows higher film cooling effectiveness than the 90° film cooling hole arrangement. As the blowing ratio increases, the cooling effectiveness is enhanced for both the 35° almost constant regardless of H/d, while H/d = 1 shows a minimum value for the angled film cooling hole.

Influence of Hole Inlet Geometry on the Film Cooling Effectiveness From Shaped Film Cooling Holes

2019 ◽  
Author(s):  
Travis B. Watson ◽  
Kyle R. Vinton ◽  
Lesley M. Wright ◽  
Daniel C. Crites ◽  
Mark C. Morris ◽  
...  
Keyword(s):  
Film Cooling ◽  
Density Ratio ◽  
Lateral Spread ◽  
Pressure Sensitive Paint ◽  
Cooling Effectiveness ◽  
Film Cooling Effectiveness ◽  
Pressure Sensitive ◽  
Inlet Geometry ◽  
Cooling Hole ◽  
Film Cooling Holes

Abstract The effect of film cooling hole inlet geometry is experimentally investigated in this study. Detailed film cooling effectiveness distributions are obtained on a flat plate using Pressure Sensitive Paint (PSP). The inlet of a traditional 12°-12°-12°, laidback, fanshaped hole varies from a traditional “round” opening to an oblong, racetrack shaped opening. In this study, a single racetrack inlet with an aspect ratio of 2:1 is compared to the round inlet. For both designs, the holes are inclined at θ = 30° relative to the mainstream. Blowing ratios of 0.5, 1.0, and 1.5 are considered as the coolant–to–mainstream density ratio varies between 1.0 and 4.0. For all cases, the freestream turbulence intensity is maintained at 7.5%. With the introduction of the racetrack shaped inlet, the coolant spreads laterally across the diffuse, laidback fanshaped outlet. The centerline film cooling effectiveness is reduced with the enhanced lateral spread of the coolant. However, the benefit of the shaped inlet is also observed with an increase in the area averaged film cooling effectiveness, compared to the traditional round inlet. Not only does the shaped inlet promote spreading of the coolant, it is also believed the racetrack shape suppresses turbulence within the hole allowing for enhanced film cooling protection near the film cooling holes.

Interaction of Flow and Film-Cooling Effectiveness Between Double-Jet Film-Cooling Holes With Various Spanwise Distances

2018 ◽  
Vol 140 (12) ◽  
Author(s):  
Jiaxu Yao ◽  
Jin Xu ◽  
Ke Zhang ◽  
Jiang Lei ◽  
Lesley M. Wright
Keyword(s):  
Flat Plate ◽  
Film Cooling ◽  
Density Ratio ◽  
Vortex Pair ◽  
Cooling Effectiveness ◽  
Film Cooling Effectiveness ◽  
Blowing Ratio ◽  
Film Cooling Holes ◽  
Two Jets ◽  
Compound Angle

The interaction of flow and film-cooling effectiveness between jets of double-jet film-cooling (DJFC) holes on a flat plate is studied experimentally. The time-averaged flow field in several axial positions (X/d = −2.0, 1.0, and 5.0) is obtained through a seven-hole probe. The downstream film-cooling effectiveness on the flat plate is measured by pressure sensitive paint (PSP). The inclination angle (θ) of all the holes is 35 deg, and the compound angle (β) is ±45 deg. Effects of the spanwise distance (p = 0, 0.5d, 1.0d, 1.5d, and 2.0d) between the two interacting jets of DJFC holes are studied, while the streamwise distance (s) is kept as 3d. The blowing ratio (M) varies as 0.5, 1.0, 1.5, and 2.0. The density ratio (DR) is maintained at 1.0. Results show that the interaction between the two jets of DJFC holes has different effects at different spanwise distances. For a small spanwise distance (p/d = 0), the interaction between the jets presents a pressing effect. The downstream jet is pressed down and kept attached to the surface by the upstream one. The effectiveness is not sensitive to blowing ratios. For mid-spanwise distances (p/d = 0.5 and 1.0), the antikidney vortex pair dominates the interaction and pushes both of the jets down, thus leading to better coolant coverage and higher effectiveness. As the spanwise distance becomes larger (p/d ≥ 1.5), the pressing effect almost disappears, and the antikidney vortex pair effect is weaker. The jets separate from each other and the coolant coverage decreases. At a higher blowing ratio, the interaction between the jets of DJFC holes happens later.

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