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.

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.

Effect of Internal Crossflow Velocity on Film Cooling Effectiveness—Part I: Axial Shaped Holes

2017 ◽  
Vol 140 (1) ◽  
Author(s):  
John W. McClintic ◽  
Joshua B. Anderson ◽  
David G. Bogard ◽  
Thomas E. Dyson ◽  
Zachary D. Webster
Keyword(s):  
Film Cooling ◽  
Velocity Ratio ◽  
Turbine Blades ◽  
Lateral Spreading ◽  
Cooling Effectiveness ◽  
Film Cooling Effectiveness ◽  
Crossflow Velocity ◽  
Density Ratios ◽  
Film Cooling Holes ◽  
Injection Rates

The effect of feeding shaped film cooling holes with an internal crossflow is not well understood. Previous studies have shown that internal crossflow reduces film cooling effectiveness from axial shaped holes, but little is known about the mechanisms governing this effect. It was recently shown that the crossflow-to-mainstream velocity ratio is important, but only a few of these crossflow velocity ratios have been studied. This effect is of concern because gas turbine blades typically feature internal passages that feed film cooling holes in this manner. In this study, film cooling effectiveness was measured for a single row of axial shaped cooling holes fed by an internal crossflow with crossflow-to-mainstream velocity ratio varying from 0.2 to 0.6 and jet-to-mainstream velocity ratios varying from 0.3 to 1.7. Experiments were conducted in a low speed flat plate facility at coolant-to-mainstream density ratios of 1.2 and 1.8. It was found that film cooling effectiveness was highly sensitive to crossflow velocity at higher injection rates while it was much less sensitive at lower injection rates. Analysis of the jet shape and lateral spreading found that certain jet characteristic parameters scale well with the crossflow-to-coolant jet velocity ratio, demonstrating that the crossflow effect is governed by how coolant enters the film cooling holes.

Adiabatic Effectiveness Measurements for a Baseline Shaped Film Cooling Hole

2014 ◽  
Author(s):  
Robert P. Schroeder ◽  
Karen A. Thole
Keyword(s):  
Film Cooling ◽  
Freestream Turbulence ◽  
Blowing Ratio ◽  
Cooling Hole ◽  
Cylindrical Holes ◽  
Shaped Hole ◽  
Adiabatic Effectiveness ◽  
Improved Performance ◽  
Density Ratios ◽  
Film Cooling Holes

Film cooling on airfoils is a crucial cooling method as the gas turbine industry seeks higher turbine inlet temperatures. Shaped film cooling holes are widely used in many designs given the improved performance over that of cylindrical holes. Although there have been numerous studies of shaped holes, there is no established baseline shaped hole to which new cooling hole designs can be compared. The goal of this study is to offer the community a shaped hole design, representative of proprietary and open literature holes that serves as a baseline for comparison purposes. The baseline shaped cooling hole design includes the following features: hole inclination angle of 30° with a 7° expansion in the forward and lateral directions; hole length of 6 diameters; hole exit-to-inlet area ratio of 2.5; and lateral hole spacing of 6 diameters. Adiabatic effectiveness was measured with this new shaped hole and was found to peak near a blowing ratio of 1.5 at density ratios of 1.2 and 1.5 as well as at both low and moderate freestream turbulence of 5%. Reductions in area-averaged effectiveness due to freestream turbulence at low blowing ratios were as high as 10%.

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.

An Investigation of Turbine Film Cooling Effectiveness With Shaped Holes and Internal Cross-Flow With Varying Operational Parameters

2016 ◽  
Author(s):  
Ellen Wilkes ◽  
Joshua Anderson ◽  
John McClintic ◽  
David Bogard
Keyword(s):  
Film Cooling ◽  
Velocity Ratio ◽  
Cross Flow ◽  
Flow Channel ◽  
Cooling Effectiveness ◽  
Film Cooling Effectiveness ◽  
Injection Angle ◽  
Shaped Hole ◽  
Adiabatic Effectiveness ◽  
Film Cooling Holes

This study focuses on specifics of gas turbine film cooling. Laboratory film cooling tests are important for industry because actual engine conditions are too hot, too small, and too fast to take accurate and high resolution measurements. Experiments are typically conducted using a plenum to feed coolant through round or shaped film cooling holes. Less common are experiments using cross-flow fed coolant, a method that flows coolant perpendicular to the mainstream flow and better represents engine designs. There are a few studies that have explored shaped holes in cross-flow, but none have looked at the effect cross-flow channel parameters other than Mach number. Here, the effectiveness of film cooling is quantified by measuring adiabatic effectiveness on a flat plate with a single row of shaped film cooling holes in cross-flow. A preliminary examination of the effect of cross-flow versus plenum fed coolant on the adiabatic effectiveness of the axial 7-7-7 shaped hole, a laidback fan-shaped hole with a 30 degree injection angle, is first conducted. Subsequently, the effects of two internal coolant parameters on film cooling effectiveness are presented: Reynold’s number inside the cross-flow channel, and velocity ratio (defined as the ratio of cross-flow channel average velocity to mainstream velocity). By measuring the effect of these parameters, a chain of relative importance can be generated and applied to future experimentation. Parameters that heavily influence film cooling effectiveness can be studied further and optimized for turbine film cooling design.

Effect of Density Ratio on Multi-Row Film Cooling Performance

2017 ◽  
Author(s):  
Michael T. Voet ◽  
Craig P. Fernandes ◽  
Zachary Little ◽  
Erik Fernandez ◽  
Jay Kapat
Keyword(s):  
Film Cooling ◽  
Momentum Flux ◽  
Velocity Ratio ◽  
Density Ratio ◽  
Diameter Ratio ◽  
Cylindrical Hole ◽  
Co2 Injection ◽  
Freestream Velocity ◽  
Blowing Ratio ◽  
Density Ratios

This study is an investigation into the effects of density ratio on the jet structure of different film cooling configurations. A simple-shaped cylindrical hole is tested at a tight spacing, which has a lateral and streamwise pitch-to-hole-diameter ratio of 7.5. Each of the holes are 3.8mm in diameter, and have a hole length-to-diameter ratio of 11.2. The holes are inclined at 20°. The cylindrical hole shapes were machined from an aluminum plate. Two different density ratios of nominally 1 and 1.5, are achieved by alternating the coolant gas between air and CO2 respectively, while maintaining a constant freestream velocity of 36.2 m/s. In order to compare cases between different densities, various ratios are independently matched for both density ratios. Blowing ratios comparisons made at 0.3 and 0.5, accompanied by comparisons of momentum flux ratio and velocity ratio at 0.1 and 0.3, respectively. Particle image velocimetry (PIV) is utilized to measure the flow field of the centerline planes of the film cooling arrays over the two density ratios. This data is then used to investigate flow interactions as coolant leaves the film cooling hole, and structure of the jet as it enters and mixes with the freestream. When comparing density ratio effects at low blowing and momentum flux ratios, increased turbulence intensities are seen closer to the surface for CO2 injection. This suggests that the overall performance of the film decreases with increasing density ratio at these low mass flux and momentum flux cases. However, when increasing blowing ratio, the higher density injection is seen to have lower levels of turbulence in the near wall region, when compared to that of the lower density fluid. This suggests that as blowing ratio increases, the higher density fluid out performs the lower density fluid. When a low constant velocity ratio is observed, the higher density fluid is seen to have decreased levels of turbulence, again suggesting that the higher density fluid out performs the low density fluid.

Density Ratio Effects on the Flow Field Emanating From Cylindrical Effusion and Trenched Film Cooling Holes

2014 ◽  
Author(s):  
Peter Schreivogel ◽  
Bernhard Kröss ◽  
Michael Pfitzner
Keyword(s):  
Flow Field ◽  
Film Cooling ◽  
Recirculation Zone ◽  
Velocity Ratio ◽  
Density Ratio ◽  
Piv Measurements ◽  
Blowing Ratio ◽  
Density Ratios ◽  
Film Cooling Holes ◽  
Cooling Air

The present paper investigates density ratio effects on the flow field of cylindrical hole effusion and trench film cooling. An extensive parametric study of varying blowing rates (M = 1; 2; 4; 6), momentum (I = 1; 2; 8; 16) and velocity ratios (VR = 0.5; 1; 2) was carried out at three different density ratios (DR = 1.33; 1.6; 2). All cases were simulated using the realizable k-ε turbulence model with enhanced wall treatment. The mainstream boundary conditions were kept constant, while the coolant mass flow and temperature were varied. Additional 2D PIV measurements in streamwise planes and planes parallel to the wall were carried out in a heated, closed loop wind tunnel with an injection of cryogenically cooled air. For constant momentum ratios, the jet core trajectories for both configurations were almost independent from the density ratio. In case of a constant blowing ratio, the jet penetration decreased with the density ratio, while it increased for a constant velocity ratio. Downstream of the trench a large recirculation zone is visible. Furthermore, cooling air is forced out of the trench in the midplane between two cooling holes.

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.

Effect of Internal Crossflow Velocity on Film Cooling Effectiveness: Part I — Axial Shaped Holes

2017 ◽  
Author(s):  
John W. McClintic ◽  
Joshua B. Anderson ◽  
David G. Bogard ◽  
Thomas E. Dyson ◽  
Zachary D. Webster
Keyword(s):  
Film Cooling ◽  
Velocity Ratio ◽  
Turbine Blades ◽  
Lateral Spreading ◽  
Cooling Effectiveness ◽  
Film Cooling Effectiveness ◽  
Crossflow Velocity ◽  
Density Ratios ◽  
Film Cooling Holes ◽  
Injection Rates

The effect of feeding shaped film cooling holes with an internal crossflow is not well understood. Previous studies have shown internal crossflow reduces film cooling effectiveness from axial shaped holes, but little is known about the mechanisms governing this effect. It was recently shown that the crossflow-to-mainstream velocity ratio is important, but only a few of these crossflow velocity ratios have been studied. This effect is of concern because gas turbine blades typically feature internal passages that feed film cooling holes in this manner. In this study, film cooling effectiveness was measured for a single row of axial shaped cooling holes fed by an internal crossflow with crossflow-to-mainstream velocity ratio varying from 0.2–0.6 and jet-to-mainstream velocity ratios varying from 0.3–1.7. Experiments were conducted in a low speed flat plate facility at coolant-to-mainstream density ratios of 1.2 and 1.8. It was found that film cooling effectiveness was highly sensitive to crossflow velocity at higher injection rates, while it was much less sensitive at lower injection rates. Analysis of the jet shape and lateral spreading found that certain jet characteristic parameters scale well with the crossflow-to-coolant jet velocity ratio, demonstrating that the crossflow effect is governed by how coolant enters the film cooling holes.

Introducing a New Test Rig for Film Cooling Measurements With Realistic Hole Inflow Conditions

2017 ◽  
Author(s):  
Marc Fraas ◽  
Tobias Glasenapp ◽  
Achmed Schulz ◽  
Hans-Jörg Bauer
Keyword(s):  
Film Cooling ◽  
Gas Flow ◽  
Test Rig ◽  
Hot Gas ◽  
Cooling Hole ◽  
Measurement Principle ◽  
Density Ratios ◽  
Operational Range ◽  
Film Cooling Holes

Further improvements in film cooling require an in-depth understanding of the influencing parameters. Therefore, a new test rig has been designed and commissioned for the assessment of novel film cooling holes under realistic conditions. The test rig is designed for generic film cooling studies. External hot gas flow as well as internal coolant passage flow are simulated by two individual flow channels connected to each other by the cooling holes. Based on a similarity analysis, the geometry of the test rig is scaled up by a factor of about 20. It furthermore offers the possibility to conduct experiments at high density ratios and realistic approach flow conditions at both cooling hole exit and inlet. The operational range of the new test rig is presented and compared to real engine conditions. It is shown that the important parameters are met and the transfer-ability of the results is ensured. Special effort is put onto the uniformity of the approaching hot gas flow, which will be demonstrated by temperature and velocity profiles. A first measurement of the heat transfer coefficient without film cooling is used to demonstrate the quality of the measurement principle.

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