The Effect of Internal Crossflow on the Adiabatic Effectiveness of Compound Angle Film Cooling Holes

2015 ◽  
Vol 137 (7) ◽  
Author(s):  
John W. McClintic ◽  
Sean R. Klavetter ◽  
James R. Winka ◽  
Joshua B. Anderson ◽  
David G. Bogard ◽  
...  
Keyword(s):  
Film Cooling ◽  
Density Ratio ◽  
Experimental Studies ◽  
Turbine Engines ◽  
Gas Turbine Engines ◽  
Experimental Conditions ◽  
Turbine Engine ◽  
Adiabatic Effectiveness ◽  
Film Cooling Holes ◽  
Compound Angle

In gas turbine engines, film cooling holes are often fed by an internal crossflow, with flow normal to the direction of the external flow around the airfoil. Many experimental studies have used a quiescent plenum to feed model film cooling holes and thus do not account for the effects of internal crossflow. In this study, an experimental flat plate facility was constructed to study the effects of internal crossflow on a row of cylindrical compound angle film cooling holes. There are relatively few studies available in literature that focus on the effects of crossflow on film cooling performance, with no studies examining the effects of internal crossflow on film cooling with round, compound angled holes. A crossflow channel allowed for coolant to flow alternately in either direction perpendicular to the mainstream flow. Experimental conditions were scaled to match realistic turbine engine conditions at low speeds. Cylindrical compound angle film cooling holes were operated at blowing ratios ranging from 0.5 to 2.0 and at a density ratio (DR) of 1.5. The results from the crossflow experiments were compared to a baseline plenum-fed configuration. This study showed that significantly greater adiabatic effectiveness was achieved for crossflow counter to the direction of coolant injection.

The Effect of Internal Cross-Flow on the Adiabatic Effectiveness of Compound Angle Film Cooling Holes

2014 ◽  
Author(s):  
John W. McClintic ◽  
Sean R. Klavetter ◽  
Joshua B. Anderson ◽  
James R. Winka ◽  
David G. Bogard ◽  
...  
Keyword(s):  
Film Cooling ◽  
Density Ratio ◽  
Experimental Studies ◽  
Cross Flow ◽  
Operating Conditions ◽  
Turbine Engines ◽  
Turbine Engine ◽  
Adiabatic Effectiveness ◽  
Film Cooling Holes ◽  
Compound Angle

In gas turbine engines, film cooling holes are often fed by an internal cross-flow, with flow normal to the direction of the external flow around the airfoil. Many experimental studies have used a quiescent plenum to feed model film cooling holes and thus do not account for the effects of internal cross-flow. In this study, an experimental flat plate facility was constructed to study the effects of internal cross-flow on a row of cylindrical compound angle film cooling holes. Operating conditions were scaled, based on coolant hole Reynolds number and turbulence level, to match realistic turbine engine conditions. A cross-flow channel allowed for coolant to flow alternately in either direction perpendicular to the mainstream flow. Film cooling holes were operated at blowing ratios ranging from 0.5 to 2.0 at a density ratio of 1.5. There are relatively few studies available in literature that focus on the effects of cross-flow on film cooling performance, with no studies examining the effects of internal cross-flow on film cooling with round, compound angled holes. This study showed that significantly greater adiabatic effectiveness was achieved for cross-flow in the opposite direction of the span-wise direction of the coolant holes and provides possible explanations for this result.

The Effect of Rib Turbulators on Film Cooling Effectiveness of Round Compound Angle Holes Fed by an Internal Cross-Flow

2016 ◽  
Vol 138 (12) ◽  
Author(s):  
Sean R. Klavetter ◽  
John W. McClintic ◽  
David G. Bogard ◽  
Jason E. Dees ◽  
Gregory M. Laskowski ◽  
...  
Keyword(s):  
Film Cooling ◽  
Density Ratio ◽  
Cross Flow ◽  
Local Pressure ◽  
Cooling Effectiveness ◽  
Film Cooling Effectiveness ◽  
Rib Turbulators ◽  
Adiabatic Effectiveness ◽  
Film Cooling Holes ◽  
Compound Angle

Early stage gas turbine blades feature complicated internal geometries in order to enhance internal heat transfer and to supply coolant for film cooling. Most film cooling experiments decouple the effect of internal coolant feed from external film cooling effectiveness, even though engine parts are commonly fed by cross-flow and feature internal rib turbulators which can affect film cooling. Experiments measuring adiabatic effectiveness were conducted to investigate the effects of turbulated perpendicular cross-flow on a row of 45 deg compound angle cylindrical film cooling holes for a total of eight internal rib configurations. The ribs were angled to the direction of prevailing internal cross-flow at two different angles: 45 deg or 135 deg. The ribs were also positioned at two different spanwise locations relative to the cooling holes: in the middle of the cooling hole pitch and slightly intersecting the holes. Experiments were conducted at a density ratio of DR = 1.5 for a range of blowing ratios including M = 0.5, 0.75, 1.0, 1.5, and 2.0. This study demonstrates that peak effectiveness can be attained through the optimization of cross-flow direction relative to the compound angle direction and rib configuration, verifying the importance of hole inlet conditions in film cooling experiments. It was found that ribs tend to reduce adiabatic effectiveness relative to a baseline, smooth-walled configuration. Rib configurations that directed the internal coolant forward in the direction of the mainstream resulted in higher peak adiabatic effectiveness. However, no other parameters could consistently be identified correlating to increased film cooling performance. It is likely that a combination of factors is responsible for influencing performance, including internal local pressure caused by the ribs, the internal channel flow field, in-hole vortices, and jet exit velocity profiles. This study also attempted to replicate the possibility that film cooling holes may intersect ribs and found that a hole which partially intersects a rib still maintains moderate levels of effectiveness.

The Effect of Rib Turbulators on Film Cooling Effectiveness of Round Compound Angle Holes Fed by an Internal Cross-Flow

2015 ◽  
Author(s):  
Sean R. Klavetter ◽  
John W. McClintic ◽  
David G. Bogard ◽  
Jason E. Dees ◽  
Gregory M. Laskowski ◽  
...  
Keyword(s):  
Film Cooling ◽  
Density Ratio ◽  
Cross Flow ◽  
Local Pressure ◽  
Cooling Effectiveness ◽  
Film Cooling Effectiveness ◽  
Rib Turbulators ◽  
Adiabatic Effectiveness ◽  
Film Cooling Holes ◽  
Compound Angle

Early stage gas turbine blades feature complicated internal geometries in order to enhance internal heat transfer and to supply coolant for film cooling. Most film cooling experiments decouple the effect of internal coolant feed from external film cooling effectiveness, even though engine parts are commonly fed by cross-flow and feature internal rib turbulators which can affect film cooling. Experiments measuring adiabatic effectiveness were conducted to investigate the effects of turbulated perpendicular cross-flow on a row of 45° compound angle cylindrical film cooling holes for a total of eight internal rib configurations. The ribs were angled to the direction of prevailing internal cross-flow at two different angles: 45° or 135°. The ribs were also positioned at two different span-wise locations relative to the cooling holes: in the middle of the cooling hole pitch, and slightly intersecting the holes. Experiments were conducted at a density ratio of DR = 1.5 for a range of blowing ratios including M = 0.5, 0.75, 1.0, 1.5, and 2.0. This study demonstrates that peak effectiveness can be attained through the optimization of cross-flow direction relative to the compound angle direction and rib configuration, verifying the importance of hole inlet conditions in film cooling experiments. It was found that ribs tend to reduce adiabatic effectiveness relative to a baseline, smooth-walled configuration. Rib configurations that directed the internal coolant forward in the direction of the mainstream resulted in higher peak adiabatic effectiveness. However, no other parameters could consistently be identified correlating to increased film cooling performance. It is likely that a combination of factors is responsible for influencing performance, including internal local pressure caused by the ribs, the internal channel flow field, in-hole vortices, and jet exit velocity profiles. This study also attempted to replicate the possibility that film cooling holes may intersect ribs and found that a hole which partially intersects a rib still maintains moderate levels of effectiveness.

scholarly journals A CFD Benchmark Study: Leading Edge Film-Cooling With Compound Angle Injection

1997 ◽  
Author(s):  
C. A. Martin ◽  
K. A. Thole
Keyword(s):  
Film Cooling ◽  
Density Ratio ◽  
Leading Edge ◽  
Stagnation Region ◽  
Injection Angle ◽  
Blowing Ratio ◽  
Adiabatic Effectiveness ◽  
Film Cooling Holes ◽  
Compound Angle ◽  
Good Agreement

This paper presents a blind CFD benchmark of a simulated leading edge for a turbine airfoil. The geometry studied was relevant for current designs with two rows of staggered film-cooling holes located at the stagnation location (θ = 0°) and at θ = 25°. Both rows of cooling holes were blowing in the same direction which was 90° relative to the streamwise direction and had an injection angle with respect to the surface of 20°. Realistic engine conditions were simulated including a density ratio of DR = 1.8 and an average blowing ratio of M = 2 for both rows of cooling holes. This blind benchmark coincided with an experimental study that took place in a wind tunnel simulation of a quarter cylinder followed by a flat afterbody. At the stagnation region, the CFD calculation overpredicted the adiabatic effectiveness because the model failed to predict a small separation region that was measured in the experiments. Good agreement was achieved, however, between the CFD predictions and the experimentally measured values of the laterally averaged adiabatic effectiveness downstream of the stagnation location. The coolant pathlines showed that flow passed from the first row of holes over the second row of cooling holes indicating a waste of the coolant.

Effect of Coolant Density on Leading Edge Showerhead Film Cooling Using PSP Measurement Technique

2013 ◽  
Author(s):  
Shiou-Jiuan Li ◽  
Shang-Feng Yang ◽  
Je-Chin Han
Keyword(s):  
Film Cooling ◽  
Density Ratio ◽  
Leading Edge ◽  
Film Cooling Effectiveness ◽  
Blowing Ratio ◽  
Pressure Sensitive ◽  
Cylindrical Holes ◽  
Film Cooling Holes ◽  
Compound Angle ◽  
Low Speed Wind Tunnel

The density ratio effect on leading edge showerhead film cooling has been studied experimentally using the pressure sensitive paint (PSP) mass transfer analogy method. Leading edge model is a blunt body with a semi-cylinder and an after body. There are two designs: seven-row and three-row of film cooling holes for simulating vane and blade, respectively. The film holes are located at 0 (stagnation row), ±15, ±30, and ±45 deg for seven-row design, and at 0 and ±30 for three-row design. Four film holes configurations are used for both test designs: radial angle cylindrical holes, compound angle cylindrical holes, radial angle shaped holes, and compound angle shaped holes. Coolant to mainstream density ratio varies from DR = 1.0, 1.5, to 2.0 while blowing ratio varies from M = 0.5 to 2.1. Experiments were conducted in a low speed wind tunnel with Reynolds number 100,900 based on mainstream velocity and diameter of the cylinder. The mainstream turbulence intensity near leading edge model is about 7%. The results show the shaped holes have overall higher film cooling effectiveness than cylindrical holes, and radial angle holes are better than compound angle holes, particularly at higher blowing ratio. Larger density ratio makes more coolant attach to the surface and increases film protection for all cases. Radial angle shaped holes provides best film cooling at higher density ratio and blowing ratio for both designs.

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.

Effect of Blowing Ratio in the Near-Stagnation Region of a Three-Row Leading Edge Film Cooling Geometry Using Large Eddy Simulations

2009 ◽  
Author(s):  
Sai Shrinivas Sreedharan ◽  
Danesh K. Tafti
Keyword(s):  
Film Cooling ◽  
Density Ratio ◽  
Leading Edge ◽  
Large Eddy Simulations ◽  
Stagnation Region ◽  
Stagnation Line ◽  
Blowing Ratio ◽  
Large Eddy ◽  
Adiabatic Effectiveness ◽  
Compound Angle

Computational studies are carried out using Large Eddy Simulations (LES) to investigate the effect of coolant to mainstream blowing ratio in a leading edge region of a film cooled vane. The three row leading edge vane geometry is modeled as a symmetric semi-cylinder with a flat afterbody. One row of coolant holes is located along the stagnation line and the other two rows of coolant holes are located at ±21.3° from the stagnation line. The coolant is injected at 45° to the vane surface with 90° compound angle injection. The coolant to mainstream density ratio is set to unity and the freestream Reynolds number based on leading edge diameter is 32000. Blowing ratios (B.R.) of 0.5, 1.0, 1.5, and 2.0 are investigated. It is found that the stagnation cooling jets penetrate much further into the mainstream, both in the normal and lateral directions, than the off-stagnation jets for all blowing ratios. Jet dilution is characterized by turbulent diffusion and entrainment. The strength of both mechanisms increases with blowing ratio. The adiabatic effectiveness in the stagnation region initially increases with blowing ratio but then generally decreases as the blowing ratio increases further. Immediately downstream of off-stagnation injection, the adiabatic effectiveness is highest at B.R. = 0.5. However, further downstream the larger mass of coolant injected at higher blowing ratios, in spite of the larger jet penetration and dilution, increases the effectiveness with blowing ratio.

Computational Fluid Dynamics Evaluations of Film Cooling Flow Scaling Between Engine and Experimental Conditions

2016 ◽  
Vol 139 (2) ◽  
Author(s):  
James L. Rutledge ◽  
Marc D. Polanka ◽  
Nathan J. Greiner
Keyword(s):  
Low Temperature ◽  
Film Cooling ◽  
Momentum Flux ◽  
Room Temperature ◽  
Density Ratio ◽  
Flux Ratio ◽  
Experimental Conditions ◽  
Cold Air ◽  
Momentum Flux Ratio ◽  
Adiabatic Effectiveness

The hostile turbine environment requires testing film cooling designs in wind tunnels that allow for appropriate instrumentation and optical access, but at temperatures much lower than in the hot section of an engine. Low-temperature experimental techniques may involve methods to elevate the coolant to freestream density ratio to match or approximately match engine conditions. These methods include the use of CO2 or cold air for the coolant while room temperature air is used for the freestream. However, the density is not the only fluid property to differ between typical wind tunnel experiments so uncertainty remains regarding which of these methods best provide scaled film cooling performance. Furthermore, matching of both the freestream and coolant Reynolds numbers is generally impossible when either mass flux ratio or momentum flux ratio is matched. A computational simulation of a film cooled leading edge geometry at high-temperature engine conditions was conducted to establish a baseline condition to be matched at simulated low-temperature experimental conditions with a 10× scale model. Matching was performed with three common coolants used in low-temperature film cooling experiments—room temperature air, CO2, and cold air. Results indicate that matched momentum flux ratio is the most appropriate for approximating adiabatic effectiveness for the case of room temperature air coolant, but matching the density ratio through either CO2 or cold coolant also has utility. Cold air was particularly beneficial, surpassing the ability of CO2 to match adiabatic effectiveness at the engine condition, even when CO2 perfectly matches the density ratio.

High Resolution Film Cooling Effectiveness Comparison of Axial and Compound Angle Holes on the Suction Side of a Turbine Vane

2006 ◽  
Author(s):  
Scot K. Waye ◽  
David G. Bogard
Keyword(s):  
High Resolution ◽  
Flat Plate ◽  
Film Cooling ◽  
Density Ratio ◽  
Suction Side ◽  
Cooling Effectiveness ◽  
Film Cooling Effectiveness ◽  
Turbine Vane ◽  
Adiabatic Effectiveness ◽  
Compound Angle

Film cooling adiabatic effectiveness for axial and compound angle holes on the suction side of a simulated turbine vane was investigated to determine the relative performance of these configurations. The effect of the surface curvature was also evaluated by comparing to previous curvature studies and flat plate film cooling results. Experiments were conducted for varying coolant density ratio, mainstream turbulence levels, and hole spacing. Results from these measurements showed that for mild curvature, 2r/d ≈ 160, flat plate results are sufficient to predict the cooling effectiveness. Furthermore, the compound angle injection improves adiabatic effectiveness for higher blowing ratios, similar to previous studies using flat plate facilities.

scholarly journals Film Cooling With Compound Angle Holes: Adiabatic Effectiveness

1994 ◽  
Author(s):  
Donald L. Schmidt ◽  
Basav Sen ◽  
David G. Bogard
Keyword(s):  
Film Cooling ◽  
Momentum Flux ◽  
Density Ratio ◽  
Flux Ratio ◽  
Test Facility ◽  
Cooling Effectiveness ◽  
Film Cooling Effectiveness ◽  
Baseline Case ◽  
Adiabatic Effectiveness ◽  
Compound Angle

Film cooling effectiveness was studied experimentally in a flat plate test facility with zero pressure gradient using a single row of inclined holes which injected high density, cryogenically cooled air. Round holes and holes with a diffusing expanded exit were directed laterally away from the freestream direction with a compound angle of 60°. Comparisons were made with a baseline case of round holes aligned with the freestream. The effects of doubling the hole spacing to six hole diameters for each geometry were also examined. Experiments were performed at a density ratio of 1.6 with a range of blowing ratios from 0.5 to 2.5 and momentum flux ratios from 0.16 to 3.9. Lateral distributions of adiabatic effectiveness results were determined at streamwise distances from 3 D to 15 D downstream of the injection holes. All hole geometries had similar maximum spatially averaged effectiveness at a low momentum flux ratio of I = 0.25, but the round and expanded exit holes with compound angle had significantly greater effectiveness at larger momentum flux ratios. The compound angle holes with expanded exits had a much improved lateral distribution of coolant near the hole for all momentum flux ratios.

Sign in / Sign up

Export Citation Format

Share Document