Experimental and Computational Investigation of Shaped Film Cooling Holes Designed to Minimize Inlet Separation

2020 ◽  
Author(s):  
Fraser B. Jones ◽  
Dale W. Fox ◽  
David G. Bogard
Keyword(s):  
Film Cooling ◽  
Velocity Ratio ◽  
Tangential Velocity ◽  
Velocity Fields ◽  
Radius Of Curvature ◽  
Large Radius ◽  
Combustion Gases ◽  
Shaped Hole ◽  
Manufacturing Technologies ◽  
Film Cooling Holes

Abstract Film cooling is used to protect turbine components from the extreme temperatures by ejecting coolant through arrays of holes to create an air buffer from the hot combustion gases. Limitations in traditional machining meant film cooling holes universally have sharp inlets which create separation regions at the hole entrance. The present study uses experimental and computational data to show that these inlet separation are a major cause of performance variation in crossflow fed film cooling holes. Three hole designs were experimentally tested by independently varying the coolant velocity ratio (VR) and the coolant channel velocitty ratio (VRc) to isolate the effects of crossflow on hole performance. Leveraging additive manufacturing technologies, the addition of a 0.25D radius fillet to the inlet of a 7-7-7 shaped hole is shown to significantly improve diffuser usage and significantly reduce variation in performance with VRc. A second AM design used a very large radius of curvature inlet to reduce biasing caused by the inlet crossflow. Experiments showed that this “swept” hole design did minimize biasing of coolant flow to one side of the shaped hole and it significantly reduced variations due to varying VRc. RANS simulations at six VR and three VRc conditions were made for each geometry to better understand how the new geometries changed the velocity field within the hole. The sharp and rounded inlets were seen to have very similar tangential velocity fields and jet biasing. Both AM inlets created more uniform, slower velocity fields entering the diffuser. The results of this paper indicate large improvements in film cooling performance can be found by leveraging AM technology.

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.

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.

Effect of Internal Crossflow Velocity on Film Cooling Effectiveness: Part II — Compound Angle Shaped Holes

2017 ◽  
Author(s):  
John W. McClintic ◽  
Joshua B. Anderson ◽  
David G. Bogard ◽  
Thomas E. Dyson ◽  
Zachary D. Webster
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Film Cooling ◽  
Velocity Ratio ◽  
Injection Rate ◽  
Cooling Effectiveness ◽  
Film Cooling Effectiveness ◽  
Crossflow Velocity ◽  
Film Cooling Holes ◽  
Compound Angle

In gas turbine engines, film cooling holes are commonly fed with an internal crossflow, the magnitude of which has been shown to have a notable effect on film cooling effectiveness. In Part I of this study, as well as in a few previous studies, the magnitude of internal crossflow velocity was shown to have a substantial effect on film cooling effectiveness of axial shaped holes. There is, however, almost no data available in the literature that shows how internal crossflow affects compound angle shaped film cooling holes. In Part II, film cooling effectiveness, heat transfer coefficient augmentation, and discharge coefficients were measured for a single row of compound angle shaped film cooling holes fed by internal crossflow flowing both in-line and counter to the span-wise direction of coolant injection. The crossflow-to-mainstream velocity ratio was varied from 0.2–0.6 and the injection velocity ratio was varied from 0.2–1.7. It was found that increasing the magnitude of the crossflow velocity generally caused degradation of the film cooling effectiveness, especially for in-line crossflow. An analysis of jet characteristic parameters demonstrated the importance of crossflow effects relative to the effect of varying the film cooling injection rate. Heat transfer coefficient augmentation was found to be primarily dependent on injection rate, although for in-line crossflow, increasing crossflow velocity significantly increased augmentation for certain conditions.

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.

Deposition Near Film Cooling Holes on a High Pressure Turbine Vane

2011 ◽  
Vol 134 (4) ◽  
Author(s):  
Weiguo Ai ◽  
Nathan Murray ◽  
Thomas H. Fletcher ◽  
Spencer Harding ◽  
Scott Lewis ◽  
...  
Keyword(s):  
Film Cooling ◽  
Elevated Temperatures ◽  
Coal Ash ◽  
Test Facility ◽  
Barrier Coating ◽  
Turbine Vane ◽  
Turbine Component ◽  
Shaped Hole ◽  
Density Ratios ◽  
Film Cooling Holes

Deposition on film-cooled turbine components was studied in an accelerated test facility. The accelerated deposition facility seeds a natural-gas burning combustor with finely ground coal ash particulate at 1180°C and 180 m/s (M=0.25). Both cylindrical and shaped holes, with and without thermal barrier coating, were studied over a range of blowing ratios from 0.5 to 4.0. Coolant density ratios were maintained at values from 2.1 to 2.4. Deposition patterns generated with the cylindrical film cooling holes indicated regions of low deposition in the path of the coolant with heightened deposition between film holes. This distinctive pattern was more accentuated at higher blowing ratios. Optical temperature measurements of the turbine component surface during deposition showed elevated temperatures between coolant paths. This temperature nonuniformity became more accentuated as deposition increased, highlighting a mechanism for deposition growth that has been documented on in-service turbines as well. The shaped-hole components exhibited little or no deposition in the region just downstream of the holes due to the distributed coolant film. Close cylindrical hole spacing of 2.25d displayed similar behavior to the shaped-hole configuration.

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%.

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.

Discharge Coefficient Measurements of Film-Cooling Holes With Expanded Exits

1998 ◽  
Vol 120 (3) ◽  
pp. 557-563 ◽  
Author(s):  
M. Gritsch ◽  
A. Schulz ◽  
S. Wittig
Keyword(s):  
Mach Number ◽  
Film Cooling ◽  
Discharge Coefficient ◽  
Pressure Ratio ◽  
Cylindrical Hole ◽  
Flow Conditions ◽  
Wide Range ◽  
Cooling Hole ◽  
Shaped Hole ◽  
Film Cooling Holes

This paper presents the discharge coefficients of three film-cooling hole geometries tested over a wide range of flow conditions. The hole geometries include a cylindrical hole and two holes with a diffuser-shaped exit portion (i.e., a fan-shaped and a laidback fan-shaped hole). The flow conditions considered were the crossflow Mach number at the hole entrance side (up to 0.6), the crossflow Mach number at the hole exit side (up to 1.2), and the pressure ratio across the hole (up to 2). The results show that the discharge coefficient for all geometries tested strongly depends on the flow conditions (crossflows at hole inlet and exit, and pressure ratio). The discharge coefficient of both expanded holes was found to be higher than of the cylindrical hole, particularly at low pressure ratios and with a hole entrance side crossflow applied. The effect of the additional layback on the discharge coefficient is negligible.

Rib Turbulator Effects on Crossflow-Fed Shaped Film Cooling Holes

2018 ◽  
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° and 135°, to assess the impact on film cooling effectiveness. Film cooling hole inlets were positioned in both pre-rib and post-rib 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.

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