Adiabatic effectiveness and heat transfer measurements of simple and trenched cylindrical holes with backward injection

The thermal management of aero gas turbine engine combustion systems commonly employs effusion-cooling in combination with various cold-side convective cooling schemes. The combustor liner incorporates many small holes which are usually set in staggered arrays and at a shallow angle to the cooled surface; relatively cold compressor delivery air is then allowed to flow through these holes to provide the full-coverage film-cooling effect. The efficient design of such systems requires robust correlations of film-cooling effectiveness and heat transfer coefficient at a range of aero-thermal conditions, and the use of appropriately validated computational models. However, the flow conditions within a combustor are characterised by particularly high turbulence levels and relatively large length scales. The experimental evidence for performance of effusion-cooling under such flow conditions is currently sparse. The work reported here is aimed at quantifying typical effusion-cooling performance at a range of combustor relevant free-stream conditions (high turbulence), and also to assess the importance of modeling the coolant to free-stream density ratio. Details of a new laboratory wind-tunnel facility for the investigation of film-cooling at high turbulence levels are reported. For a typical combustor effusion geometry that uses cylindrical holes, spatially resolved measurements of adiabatic effectiveness, heat transfer coefficient and net heat flux reduction are presented for a range of blowing ratios (0.48 to 2), free-stream turbulence conditions (4 and 22%) and density ratios (0.97 and 1.47). The measurements reveal that elevated free-stream turbulence impacts on both the adiabatic effectiveness and heat transfer coefficient, although this is dependent upon the blowing ratio being employed and particularly the extent to which the coolant jets detach from the surface. At low blowing ratios the presence of high turbulence levels causes increased lateral spreading of the coolant adjacent to the injection points, but more rapid degradation in the downstream direction. At high blowing ratios, high turbulence levels cause a modest increase in effectiveness due to turbulent transport of the detached coolant fluid. Additionally, the augmentation of heat transfer coefficient caused by the coolant injection is seen to be increased at high free-stream turbulence levels.

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Effect of a Ceramic Matrix Composite Surface on Film Cooling

10.1115/gt2021-59602 ◽

2021 ◽

Author(s):

Peter H. Wilkins ◽

Stephen P. Lynch ◽

Karen A. Thole ◽

San Quach ◽

Tyler Vincent ◽

...

Keyword(s):

Heat Transfer ◽

Matrix Composite ◽

Film Cooling ◽

Gas Turbines ◽

Ceramic Matrix Composite ◽

Ceramic Matrix ◽

Composite Surface ◽

Minimal Impact ◽

Cooling Hole ◽

Adiabatic Effectiveness

Abstract Ceramic matrix composite (CMC) parts create the opportunity for increased turbine entry temperatures within gas turbines. To achieve the highest temperatures possible, film cooling will play an important role in allowing turbine entry temperatures to exceed acceptable surface temperatures for CMC components, just as it does for the current generation of gas turbine components. Film cooling over a CMC surface introduces new challenges including roughness features downstream of the cooling holes and changes to the hole exit due to uneven surface topography. To better understand these impacts, this study presents flowfield and adiabatic effectiveness CFD for a 7-7-7 shaped film cooling hole at two CMC weave orientations. The CMC surface selected is a 5 Harness Satin weave pattern that is examined at two different orientations. To understand the ability of steady RANS to predict flow and convective heat transfer over a CMC surface, the weave surface is initially simulated without film and compared to previous experimental results. The simulation of the weave orientation of 0°, with fewer features projecting into the flow, matches fairly well to the experiment, and demonstrates a minimal impact on film cooling leading to only slightly lower adiabatic effectiveness compared to a smooth surface. However, the simulation of the 90° orientation with a large number of protruding features does not match the experimentally observed surface heat transfer. The additional protruding surface produces degraded film cooling performance at low blowing ratios but is less sensitive to blowing ratio, leading to improved relative performance at higher blowing ratios, particularly in regions far downstream of the hole.

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Freestream Flow Effects on Film Effectiveness and Heat Transfer Coefficient Augmentation for Compound Angle Shaped Holes

Volume 5C: Heat Transfer ◽

10.1115/gt2017-64853 ◽

2017 ◽

Cited By ~ 5

Author(s):

Joshua B. Anderson ◽

John W. McClintic ◽

David G. Bogard ◽

Thomas E. Dyson ◽

Zachary Webster

Keyword(s):

Heat Transfer ◽

Boundary Layer ◽

Heat Transfer Coefficient ◽

Transfer Coefficient ◽

Layer Thickness ◽

Film Cooling ◽

Gas Turbines ◽

Boundary Layer Thickness ◽

Adiabatic Effectiveness ◽

Compound Angle

The use of compound-angled shaped film cooling holes in gas turbines provides a method for cooling regions of extreme curvature on turbine blades or vanes. These configurations have received surprisingly little attention in the film cooling literature. In this study, a row of laid-back fanshaped holes based on an open-literature design, were oriented at a 45-degree compound angle to the approaching freestream flow. In this study, the influence of the approach flow boundary layer thickness and character were experimentally investigated. A trip wire and turbulence generator were used to vary the boundary layer thickness and freestream conditions from a thin laminar boundary layer flow to a fully turbulent boundary layer and freestream at the hole breakout location. Steady-state adiabatic effectiveness and heat transfer coefficient augmentation were measured using high-resolution IR thermography, which allowed the use of an elevated density ratio of DR = 1.20. The results show adiabatic effectiveness was generally lower than for axially-oriented holes of the same geometry, and that boundary layer thickness was an important parameter in predicting effectiveness of the holes. Heat transfer coefficient augmentation was highly dependent on the freestream turbulence levels as well as boundary layer thickness, and significant spatial variations were observed.

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The Application of Adiabatic Film Cooling Effectiveness to Non-Adiabatic Blade Cooling Design

1983 Joint Power Generation Conference: GT Papers ◽

10.1115/83-jpgc-gt-1 ◽

1983 ◽

Author(s):

C. P. Lee ◽

J. C. Han

Keyword(s):

Heat Transfer ◽

Film Cooling ◽

Heat Transfer Analysis ◽

Adiabatic Wall ◽

Cooling Effectiveness ◽

Film Cooling Effectiveness ◽

Transfer Parameter ◽

Adiabatic Effectiveness ◽

C 32 ◽

Heat Transfer Parameter

The effect of heat transfer on film cooling has been studied analytically. The proposed model shows that the non-adiabatic film cooling effectiveness will increase with increasing of the heat transfer parameter, Ū / (ρVCp)2, on the convex, the flat and the concave walls over the entire range of film cooling parameter, X/MS. On the convex wall with a blowing rate, M, of 0.51 and a heat transfer parameter of 10−3 at the typical engine conditions, the non-adiabatic effectiveness can be higher than the adiabatic effectiveness by 45% at a film cooling parameter of 103; while the film temperature can be lower than the adiabatic wall by 18°C (32°F) at a dimensionless distance of 500. The model can be extended and applied to the heat transfer analysis for any kind of turbine blade with film cooling.

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Letterbox Trailing Edge Heat Transfer: Effects of Blowing Rate, Reynolds Number, and External Turbulence on Heat Transfer and Film Cooling Effectiveness

Journal of Turbomachinery ◽

10.1115/1.3106703 ◽

2009 ◽

Vol 132 (1) ◽

Cited By ~ 12

Author(s):

N. J. Fiala ◽

I. Jaswal ◽

F. E. Ames

Keyword(s):

Heat Transfer ◽

Reynolds Number ◽

Pressure Drop ◽

Flow Rate ◽

Film Cooling ◽

Suction Surface ◽

Trailing Edge ◽

Film Cooling Effectiveness ◽

Blowing Ratio ◽

Adiabatic Effectiveness

Heat transfer and film cooling distributions have been acquired for a vane trailing edge with letterbox partitions. Additionally, pressure drop data have been experimentally determined across a pin fin array and a trailing edge slot with letterbox partitions. The pressure drop across the array and letterbox trailing edge arrangement was measurably higher than for the gill slot geometry. Experimental data for the partitions and the inner suction surface region downstream from the slot have been acquired over a four-to-one range in vane exit condition Reynolds number (500,000, 1,000,000, and 2,000,000), with low (0.7%), grid (8.5%), and aerocombustor (13.5%) turbulence conditions. At these conditions, both heat transfer and adiabatic film cooling distributions have been documented over a range of blowing ratios (0.47≤M≤1.9). Heat transfer distributions on the inner suction surface downstream from the slot ejection were found to be dependent on both ejection flow rate and external conditions. Heat transfer on the partition side surfaces correlated with both exit Reynolds number and blowing ratio. Heat transfer on partition top surfaces largely correlated with exit Reynolds number but blowing ratio had a small effect at higher values. Generally, adiabatic film cooling levels on the inner suction surface are high but decrease near the trailing edge and provide some protection for the trailing edge. Adiabatic effectiveness levels on the partitions correlate with blowing ratio. On the partition sides adiabatic effectiveness is highest at low blowing ratios and decreases with increasing flow rate. On the partition tops adiabatic effectiveness increases with increasing blowing ratio but never exceeds the level on the sides. The present paper, together with a companion paper that documents letterbox trailing edge aerodynamics, is intended to provide engineers with the heat transfer and aerodynamic loss information needed to develop and compare competing trailing edge designs.

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Influence of Flow Structure on Shaped Hole Film Cooling Performance

Volume 4: Heat Transfer, Parts A and B ◽

10.1115/gt2010-23032 ◽

2010 ◽

Cited By ~ 11

Author(s):

Benoit Laveau ◽

Reza S. Abhari

Keyword(s):

Flow Structure ◽

Thermal Performance ◽

Turbine Blades ◽

Density Ratio ◽

Operating Conditions ◽

Stereoscopic Particle Image Velocimetry ◽

Infrared Measurements ◽

Cylindrical Holes ◽

Shaped Hole ◽

Adiabatic Effectiveness

Shaped holes are used on modern turbine blades for their higher performance and greater lateral coolant spreading compared to classic streamwise angled holes. This study incorporates measurements and observations from a shaped hole geometry undertaken at ETH Zurich in which a row of laterally expanded diffusely shaped holes is compared to the classic row of streamwise round holes. Infrared measurements provide high-resolution data of the adiabatic effectiveness and three dimensional velocity measurements are carried out through stereoscopic Particle Image Velocimetry. Both experiments are run for similar operating conditions allowing a comparison to be made between the flow structure and the thermal performance. The adiabatic effectiveness is seen to be higher for shaped holes compared to cylindrical holes: in particular the laterally averaged values are higher due to a larger lateral spreading of the coolant. The work presented here shows the first results on the limited influence of the density ratio on the thermal performance. The performance is also influenced by the vortical structure. The typical counter-rotating vortex pair which is completed by another pair of anti-kidney vortices is observed with their strength being clearly reduced compared to the example with cylindrical holes. The doubled structure and the reduced strength change the behavior of the jet, explaining the higher performance of a jet with shaped holes. The vertical motion leading to lift-off is reduced, so the jet remains close to the surface even at high blowing rates. The goal of this article is to present data for the thermal performance and flow field of shaped holes and then explain the relationship between the two.

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Effects of Free-Stream Turbulence and Surface Roughness on Film Cooling

Volume 4: Heat Transfer; Electric Power; Industrial and Cogeneration ◽

10.1115/96-gt-462 ◽

1996 ◽

Cited By ~ 21

Author(s):

Donald L. Schmidt ◽

David G. Bogard

Keyword(s):

Heat Transfer ◽

Surface Roughness ◽

Heat Transfer Coefficient ◽

Transfer Coefficient ◽

Film Cooling ◽

Momentum Flux ◽

Free Stream ◽

Cooling Performance ◽

Free Stream Turbulence ◽

Adiabatic Effectiveness

A flat plate test section was used to study how high free-stream turbulence with large turbulence length scales, representative of the turbine environment, affect the film cooling adiabatic effectiveness and heat transfer coefficient for a round hole film cooling geometry. This study also examined cooling performance with combined high free-stream turbulence and a rough surface which simulated the roughness representative of an in-service turbine. The injection was from a single row of film cooling holes with injection angle of 30°. The density ratio of the injectant to the mainstream was 2.0 for the adiabatic effectiveness tests, and 1.0 for the heat transfer coefficient tests. Streamwise and lateral distributions of adiabatic effectiveness and heat transfer coefficients were obtained at locations from 2 to 90 hole diameters downstream. At small to moderate momentum flux ratios, which would normally be considered optimum blowing conditions, high free-stream turbulence dramatically decreased adiabatic effectiveness. However, at large momentum flux ratios, conditions for which the film cooling jet would normally be detached, high free-stream turbulence caused an increase in adiabatic effectiveness. The combination of high free-stream turbulence with surface roughness resulted in an increase in adiabatic effectiveness relative to the smooth wall with high free-stream turbulence. Heat transfer rates were relatively unaffected by a film cooling injection. The key result from this study was a substantial increase in the momentum flux ratios for maximum film cooling performance which occurred for high free-stream turbulence and surface roughness conditions which are more representative of actual turbine conditions.

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Heat Transfer Measurements Downstream of Trenched Film Cooling Holes Using a Novel Optical Two-Layer Measurement Technique

Journal of Turbomachinery ◽

10.1115/1.4031919 ◽

2015 ◽

Vol 138 (3) ◽

Cited By ~ 3

Author(s):

Peter Schreivogel ◽

Michael Pfitzner

Keyword(s):

Heat Transfer ◽

Heat Flux ◽

Heat Transfer Coefficient ◽

Transfer Coefficient ◽

Film Cooling ◽

Slight Reduction ◽

Superposition Method ◽

Cooling Effectiveness ◽

Cylindrical Holes ◽

The Heat Transfer Coefficient

A new approach for steady-state heat transfer measurements is proposed. Temperature distributions are measured at the surface and a defined depth inside the wall to provide boundary conditions for a three-dimensional heat flux calculation. The practical application of the technique is demonstrated by employing a superposition method to measure heat transfer and film cooling effectiveness downstream of two different 0.75D deep narrow trench geometries and cylindrical holes. Compared to the cylindrical holes, both trench geometries lead to an augmentation of the heat transfer coefficient supposedly caused by the highly turbulent attached cooling film emanating from the trenches. Areas of high heat transfer are visible, where recirculation bubbles or large amounts of coolant are expected. Increasing the density ratio from 1.33 to 1.60 led to a slight reduction of the heat transfer coefficient and an increased cooling effectiveness. Both trenches provide a net heat flux reduction (NHFR) superior to that of cylindrical holes, especially at the highest momentum flux ratios.

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Leading Edge Film Cooling Effects on Turbine Blade Heat Transfer

Volume 4: Heat Transfer; Electric Power; Industrial and Cogeneration ◽

10.1115/95-gt-275 ◽

1995 ◽

Cited By ~ 1

Author(s):

Vijay K. Garg ◽

Raymond E. Gaugler

Keyword(s):

Heat Transfer ◽

Heat Transfer Coefficient ◽

Transfer Coefficient ◽

Mass Flow ◽

Film Cooling ◽

Three Dimensional ◽

Stagnation Temperature ◽

Flow Ratio ◽

Adiabatic Effectiveness ◽

Mass Flow Ratio

An existing three-dimensional Navier-Stokes code (Arnone et al., 1991), modified to include film cooling considerations (Garg and Gaugler, 1994), has been used to study the effect of spanwise pitch of shower-head holes and coolant to mainstream mass flow ratio on the adiabatic effectiveness and heat transfer coefficient on a film-cooled turbine vane. The mainstream is akin to that under real engine conditions with stagnation temperature = 1900 K and stagnation pressure = 3 MPa. It is found that with the coolant to mainstream mass flow ratio fixed, reducing P, the spanwise pitch for shower-head holes, from 7.5 d to 3.0 d, where d is the hole diameter, increases the average effectiveness considerably over the blade surface. However, when P/d = 7.5, increasing the coolant mass flow increases the effectiveness on the pressure surface but reduces it on the suction surface due to coolant jet lift-off. For P/d = 4.5 or 3.0, such an anomaly does not occur within the range of coolant to mainstream mass flow ratios analyzed. In all cases, adiabatic effectiveness and heat transfer coefficient are highly three-dimensional.

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