Effect of Surface Roughness on Local Heat Transfer and Film Cooling Effectiveness

1995 ◽  
Author(s):  
Douglas N. Barlow ◽  
Yong W. Kim
Keyword(s):  
Heat Transfer ◽  
Film Cooling ◽  
Smooth Surface ◽  
Rough Surfaces ◽  
Local Heat Transfer ◽  
Local Heat ◽  
Transfer Coefficients ◽  
Cooling Effectiveness ◽  
Film Cooling Effectiveness ◽  
Heat Transfer Coefficients

An experimental investigation of film cooling on rough surfaces has been accomplished at a Reynolds number and dimensionless boundary layer momentum thickness found in current high performance first stage turbine vanes. A transient experimental method using thermochromic liquid crystals is employed to determine both local heat transfer coefficients and film cooling effectiveness values on planar rough surfaces. Two surface roughness configurations are investigated with a single row of cooling holes spaced three diameters apart and inclined 30° to the mainstream flow. The mainstream turbulence level at the point of film injection is 8.5% and the density ratio considered is approximately 1.0. The influence of roughness on the centerline film cooling effectiveness, laterally averaged film cooling effectiveness, laterally averaged heat transfer coefficients, as well as area averaged values are presented. It is found that the presence of roughness causes a decrease in the film cooling effectiveness over that of the smooth surface for the range of experimental parameters considered in this study. In addition, significant lateral smoothing in film cooling effectiveness distribution is observed for the rougher surfaces. Measured heat transfer coefficients on rough surfaces show a trend of monotonic increase with blowing ratio. However, such increase is not as great as that for the case of smooth surface.

Film-Cooling Characteristics of Pressure-Side Discharge Slots in an Accelerating Mainstream Flow

2005 ◽  
Author(s):  
Yong W. Kim ◽  
Chad Coon ◽  
Hee-Koo Moon
Keyword(s):  
Heat Transfer ◽  
Film Cooling ◽  
Local Heat Transfer ◽  
Local Heat ◽  
Transfer Coefficients ◽  
Cooling Effectiveness ◽  
Film Cooling Effectiveness ◽  
Heat Transfer Coefficients ◽  
Blowing Ratio ◽  
Mainstream Flow

Pressure-side discharge is commonly employed in turbine blades and nozzle guide vanes to keep the trailing edge metal temperatures within an allowable limit while minimizing aerodynamic penalties. Despite its widespread use, film-cooling data of the discharge slot are scarce in open literature. The objectives of the present experimental study were to measure detailed local heat transfer and film-cooling effectiveness from a 10x scale trailing-edge model of an industrial gas turbine airfoil in a low speed wind tunnel. To simulate the mainstream flow acceleration in vane and blade row passages, a linear velocity gradient was imposed using an adjustable top wall. The present work employed the composite slab quasi-steady liquid crystal method that allows measurements of local heat transfer coefficients and film-cooling effectiveness from two related tests. With this technique, the heat transfer measurement can be performed in a cold wind tunnel. The coolant-to-mainstream blowing ratio was varied between 0.25 and 1.0. The slot hydraulic diameter based Reynolds number ranged from 4,760 to 19,550. The coolant-to-mainstream density ratio was fixed at 0.95. Slot discharge coefficients were also measured with mainstream acceleration. Both local heat transfer coefficients and film-cooling effectiveness displayed a strong dependency on blowing ratio and mainstream acceleration. However, the discharge coefficients showed little dependency on the mainstream acceleration.

Heat Transfer Coefficients and Film Cooling Effectiveness of Transonic Turbine Vane Suction Surface Using TSP Technique

2016 ◽  
Author(s):  
Chao-Cheng Shiau ◽  
Nafiz H. K. Chowdhury ◽  
Shang-Feng Yang ◽  
Je-Chin Han ◽  
Alexander MirzaMoghadam ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Film Cooling ◽  
Local Heat Transfer ◽  
Local Heat ◽  
Transfer Coefficients ◽  
Suction Surface ◽  
Cooling Effectiveness ◽  
Film Cooling Effectiveness ◽  
Heat Transfer Coefficients ◽  
Compound Angle

This paper experimentally studies the effect of transonic flow on local heat transfer coefficients and film cooling effectiveness distributions of a turbine vane’s suction surface with compound-angle shaped-hole configuration. A Temperature Sensitive Paint (TSP) method is used to determine the local heat transfer coefficients and film cooling effectiveness simultaneously. Tests were performed in a five-vane annular-sector cascade blow-down facility. The exit Mach numbers are controlled to be 0.7 and 0.9, from subsonic to transonic conditions. Compressed air is used as coolant with a coolant-to-mainstream density ratio 0.91 on film cooling and heat transfer study. Three averaged coolant-to-mainstream blowing ratios in the range, 0.7, 1.0, and 1.6 are investigated. The test vane features three rows of radial-angle cylindrical holes around the leading edge, and two rows of compound-angle shaped holes on the suction side. Effects of blowing ratio and exit Mach number on the vane suction surface heat transfer and film cooling effectiveness distributions are obtained, and the results are presented and explained in this investigation.

Heat Transfer Coefficients and Film Cooling Effectiveness on the Squealer Tip of a Gas Turbine Blade

2003 ◽  
Vol 125 (4) ◽  
pp. 648-657 ◽  
Author(s):  
Jae Su Kwak ◽  
Je-Chin Han
Keyword(s):  
Heat Transfer ◽  
Gas Turbine ◽  
Turbine Blade ◽  
Film Cooling ◽  
Rotor Blade ◽  
Transfer Coefficients ◽  
Cooling Effectiveness ◽  
Film Cooling Effectiveness ◽  
Heat Transfer Coefficients ◽  
Blowing Ratio

Experimental investigations were performed to measure the detailed heat transfer coefficients and film cooling effectiveness on the squealer tip of a gas turbine blade in a five-bladed linear cascade. The blade was a two-dimensional model of a first stage gas turbine rotor blade with a profile of the GE-E3 aircraft gas turbine engine rotor blade. The test blade had a squealer (recessed) tip with a 4.22% recess. The blade model was equipped with a single row of film cooling holes on the pressure side near the tip region and the tip surface along the camber line. Hue detection based transient liquid crystals technique was used to measure heat transfer coefficients and film cooling effectiveness. All measurements were done for the three tip gap clearances of 1.0%, 1.5%, and 2.5% of blade span at the two blowing ratios of 1.0 and 2.0. The Reynolds number based on cascade exit velocity and axial chord length was 1.1×106 and the total turning angle of the blade was 97.9 deg. The overall pressure ratio was 1.2 and the inlet and exit Mach numbers were 0.25 and 0.59, respectively. The turbulence intensity level at the cascade inlet was 9.7%. Results showed that the overall heat transfer coefficients increased with increasing tip gap clearance, but decreased with increasing blowing ratio. However, the overall film cooling effectiveness increased with increasing blowing ratio. Results also showed that the overall film cooling effectiveness increased but heat transfer coefficients decreased for the squealer tip when compared to the plane tip at the same tip gap clearance and blowing ratio conditions.

Transient Liquid Crystal Technique for Convective Heat Transfer on Rough Surfaces

1995 ◽  
Author(s):  
Douglas N. Barlow ◽  
Yong W. Kim
Keyword(s):  
Heat Transfer ◽  
Rough Surfaces ◽  
Empirical Relationship ◽  
Local Heat Transfer ◽  
Local Heat ◽  
Test Method ◽  
Planar Surface ◽  
Transfer Coefficients ◽  
Heat Transfer Coefficients ◽  
Turbine Stator

The local heat transfer coefficients are obtained on a rough planar surface simulating in-service turbine stator vane sections. A transient experimental technique is presented that permits the determination of local heat transfer coefficients for a rough planar surface using thermochromic liquid crystals. The technique involves the use of a composite test surface in the form of a thin foil of stainless steel with roughness elements laminated over a transparent substrate. Tests are conducted on a splitter plate to provide momentum boundary layer thicknesses to roughness heights appropriate for actual turbine stator vanes. Data are reported for two roughness geometries and two free stream velocities. The range of Reynolds numbers along with the ratio of average roughness value to momentum thickness matches conditions encountered on the pressure side of the first stage stator vanes in current high performance turbofan engines. A numerical simulation is conducted to validate the test method. Results for the investigated rough surfaces are compared with an available empirical relationship.

Heat Transfer and Film Cooling on a Contoured Blade Endwall With Platform Gap Leakage

2017 ◽  
Vol 139 (5) ◽  
Author(s):  
Stephen P. Lynch ◽  
Karen A. Thole
Keyword(s):  
Heat Transfer ◽  
Turbine Blade ◽  
Film Cooling ◽  
Vortical Flow ◽  
Leakage Flow ◽  
Transfer Coefficients ◽  
Cooling Effectiveness ◽  
Film Cooling Effectiveness ◽  
Heat Transfer Coefficients ◽  
Manufacturing Assembly

Turbine blade components in an engine are typically designed with gaps between parts due to manufacturing, assembly, and operational considerations. Coolant is provided to these gaps to limit the ingestion of hot combustion gases. The interaction of the gaps, their leakage flows, and the complex vortical flow at the endwall of a turbine blade can significantly impact endwall heat transfer coefficients and the effectiveness of the leakage flow in providing localized cooling. In particular, a platform gap through the passage, representing the mating interface between adjacent blades in a wheel, has been shown to have a significant effect. Other important turbine blade features present in the engine environment are nonaxisymmetric contouring of the endwall, and an upstream rim seal with a gaspath cavity, which can reduce and increase endwall vortical flow, respectively. To understand the platform gap leakage effect in this environment, measurements of endwall heat transfer, and film cooling effectiveness were performed in a scaled blade cascade with a nonaxisymmetric contour in the passage. A rim seal with a cavity, representing the overlap interface between a stator and rotor, was included upstream of the blades and a nominal purge flowrate of 0.75% of the mainstream was supplied to the rim seal. The results indicated that the endwall heat transfer coefficients increased as the platform gap net leakage increased from 0% to 0.6% of the mainstream flowrate, but net heat flux to the endwall was reduced due to high cooling effectiveness of the leakage flow.

Film Cooling on Highly Loaded Blades With Main Flow Separation—Part I: Heat Transfer

2012 ◽  
Vol 135 (1) ◽  
Author(s):  
Reinaldo A. Gomes ◽  
Reinhard Niehuis
Keyword(s):  
Heat Transfer ◽  
Flow Separation ◽  
Film Cooling ◽  
Separation Bubble ◽  
Leading Edge ◽  
Local Heat Transfer ◽  
Local Heat ◽  
Main Flow ◽  
Cooling Effectiveness ◽  
Film Cooling Effectiveness

Film cooling experiments were run at the high speed cascade wind tunnel of the University of the Federal Armed Forces Munich. The investigations were carried out with a linear cascade of highly loaded turbine blades. The main objectives of the tests were to assess the film cooling effectiveness and the heat transfer in zones with main flow separation. Therefore, the blades were designed to force the flow to detach on the pressure side shortly downstream of the leading edge and reattach at about half of the axial chord. In this zone, film cooling rows are placed among others for a reduction of the size of the separation bubble. The analyzed region on the blade is critical due to the high heat transfer present at the leading edge and at the reattachment line after the main flow separation. Film cooling can contribute to a reduction of the size of the separation bubble reducing aerodynamic losses, however, in general, it increases heat transfer due to turbulent mixing. The reduction of the size of the separation bubble might also be twofold, since it acts like a thermal insulator on the blade and reducing the size of the bubble might lead to a stronger heating of the blade. Film cooling should, therefore, take both into account: first, a proper protection of the surface and second, reducing aerodynamic losses, diminishing the extension of the main flow separation. While experimental results of the adiabatic film cooling effectiveness were shown in previous publications, the local heat transfer is analyzed in this paper. Emphasis is also placed upon analyzing, in detail, the flow separation process. Furthermore, the tests comprise the analysis of the effect of different outlet Mach and Reynolds numbers and film cooling. In part two of this paper, the overall film cooling effectiveness is addressed. Local heat transfer is still difficult to predict with modern numerical tools and this is especially true for complex flows with flow separation. Some numerical results with the Reynolds averaged Navier-Stokes (RANS) and large eddy simulation (LES) show the capability of a commercial solver in predicting the heat transfer.

Film Cooling From a Row of Holes With Both Ends Embedded in Transverse Slots

2008 ◽  
Author(s):  
D. H. Zhang ◽  
L. Sun ◽  
Q. Y. Chen ◽  
M. Lin ◽  
M. Zeng ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Film Cooling ◽  
Aerodynamic Performance ◽  
Transfer Coefficients ◽  
Cooling Effectiveness ◽  
Cooling Performance ◽  
Film Cooling Effectiveness ◽  
Heat Transfer Coefficients ◽  
Discharge Coefficients ◽  
Cylindrical Holes

Embedding a row of typical cylindrical holes in a transverse slot can improve the cooling performance. Rectangular slots can increase the cooling effectiveness but is at the cost of decreasing of discharge coefficients. An experiment is conducted to examine the effects of an overlying transverse inclined trench on the film cooling performance of axial holes. Four different trench configurations are tested including the baseline inclined cylindrical holes. The influence of the geometry of the upstream lip of the exit trench and the geometry of the inlet trench on cooling performance is examined. Detailed film cooling effectiveness and heat transfer coefficients are obtained separately using the steady state IR thermography technique. The discharge coefficients are also acquired to evaluate the aerodynamic performance of different hole configurations. The results show that the film cooling holes with both ends embedded in slots can provide higher film cooling effectiveness and lower heat transfer coefficients; it also can provide higher discharge coefficients whilst retaining the mechanical strength of a row of discrete holes. The cooling performance and the aerodynamic performance of the holes with both ends embedded in inclined slots are superior to the holes with only exit trenched. To a certain extent, the configuration of the upstream lip of the exit trench affects the cooling performance of the downstream of the trench. The filleting for the film hole inlet avail the improvement of the cooling effect, but not for the film hole outlet. Comparing film cooling with embedded holes to unembedded holes, the overall heat flux ratio shows that the film holes with both ends embedded in slots and filleting for the film hole inlet can produce the highest heat flux reduction.

scholarly journals High-Resolution Measurements of Local Heat Transfer Coefficients From Discrete Hole Film Cooling

1999 ◽  
Vol 123 (4) ◽  
pp. 749-757 ◽  
Author(s):  
S. Baldauf ◽  
A. Schulz ◽  
S. Wittig
Keyword(s):  
Heat Transfer ◽  
High Resolution ◽  
Film Cooling ◽  
Density Ratio ◽  
Local Heat Transfer ◽  
Local Heat ◽  
Transfer Coefficients ◽  
Heat Transfer Coefficients ◽  
Wide Range ◽  
Surface Patterns

Local heat transfer coefficients on a flat plate surface downstream a row of cylindrical ejection holes were investigated. The parameters blowing angle, hole pitch, blowing rate, and density ratio were varied over a wide range, emphasizing engine relevant conditions. A high-resolution IR-thermography technique was used for measuring surface temperature fields. Local heat transfer coefficients were obtained from a Finite Element analysis. IR-determined surface temperatures and backside temperatures of the cooled test plate measured with thermocouples were applied as boundary conditions in this heat flux computation. The superposition approach was employed to obtain the heat transfer coefficient hf based on the difference between actual wall temperatures and adiabatic wall temperatures in the presence of film cooling. The hf data are given for an engine relevant density ratio of 1.8. Therefore, heat transfer results with different wall temperature conditions and adiabatic film cooling effectiveness results for identical flow situations (i.e., constant density ratios) were combined. Characteristic surface patterns of the locally resolved heat transfer coefficients hf are recognized and quantified as the different ejection parameters are changed. The detailed results are used to discuss the specific local heat transfer behavior in the presence of film cooling. They also provide a base of surface data essential for the validation of the heat transfer capabilities of CFD codes in discrete hole film cooling.

Film Cooling on Highly Loaded Blades With Main Flow Separation—Part II: Overall Film Cooling Effectiveness

2012 ◽  
Vol 135 (1) ◽  
Author(s):  
Reinaldo A. Gomes ◽  
Reinhard Niehuis
Keyword(s):  
Heat Transfer ◽  
Flow Separation ◽  
Film Cooling ◽  
Separation Bubble ◽  
Leading Edge ◽  
Local Heat Transfer ◽  
Local Heat ◽  
Main Flow ◽  
Cooling Effectiveness ◽  
Film Cooling Effectiveness

Film cooling experiments were run at the high speed cascade wind tunnel of the University of the Federal Armed Forces Munich. The investigations were carried out with a linear cascade of highly loaded turbine blades. The main targets of the tests were to assess the film cooling effectiveness and the heat transfer in zones with main flow separation. Therefore the blades were designed to force the flow to detach on the pressure side shortly downstream of the leading edge and it reattaches at about half of the axial chord. In this zone, film cooling rows are placed among others for reduction of the size of the separation bubble. The analyzed region on the blade is critical due to the high heat transfer present at the leading edge and at the reattachment line after main flow separation. Film cooling can contribute to a reduction of the size of the separation bubble reducing aerodynamic losses but increases in general heat transfer due to turbulent mixing. The reduction of the size of the separation bubble might also be two-fold since it acts like a thermal insulator on the blade and reducing the size of the bubble might lead to stronger heating of the blade. Film cooling should therefore take into account both: firstly, a proper protection of the surface, and secondly, reduce aerodynamic losses diminishing the extension of the main flow separation. The overall effectiveness of film cooling for a real engine has to combine heat transfer with film cooling effect. In this paper, the overall effectiveness of film cooling, combining results from measurements of the adiabatic film cooling effectiveness and the local heat transfer coefficient are shown. The tests comprise the analysis of the effect of different outlet Mach and Reynolds numbers at engine relevant values and film cooling ratio. A new parameter is introduced which allows for the evaluation of the effect of film cooling accounting at the same time for the change of local heat transfer coefficient. To the authors’ opinion this parameter allows a better, physically based assessment than the strategy using the so-called heat flux ratio. A parameter study is carried out in order to benchmark the effect of changes of the blade design.

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