The Effect of High Free-Stream Turbulence on Film Cooling Effectiveness

1996 ◽  
Vol 118 (4) ◽  
pp. 814-825 ◽  
Author(s):  
J. P. Bons ◽  
C. D. MacArthur ◽  
R. B. Rivir
Keyword(s):  
Film Cooling ◽  
Free Stream ◽  
Density Ratio ◽  
Constant Density ◽  
Injection Hole ◽  
Adiabatic Wall ◽  
Cooling Effectiveness ◽  
Film Cooling Effectiveness ◽  
Single Row ◽  
Free Stream Turbulence

This study investigated the adiabatic wall cooling effectiveness of a single row of film cooling holes injecting into a turbulent flat plate boundary layer below a turbulent, zero pressure gradient free stream. Levels of free-stream turbulence (Tu) up to 17.4 percent were generated using a method that simulates conditions at a gas turbine combustor exit. Film cooling was injected from a single row of five 35 deg slant-hole injectors (length/diameter = 3.5, pitch/diameter = 3.0) at blowing ratios from 0.55 to 1.85 and at a nearly constant density ratio (coolant density/free-stream density) of 0.95. Film cooling effectiveness data are presented for Tu levels ranging from 0.9 to 17 percent at a constant free-stream Reynolds number based on injection hole diameter of 19,000. Results show that elevated levels of free-stream turbulence reduce film cooling effectiveness by up to 70 percent in the region directly downstream of the injection hole due to enhanced mixing. At the same time, high free-stream turbulence also produces a 50–100 percent increase in film cooling effectiveness in the region between injection holes. This is due to accelerated spanwise diffusion of the cooling fluid, which also produces an earlier merger of the coolant jets from adjacent holes.

The Effect of High Freestream Turbulence on Film Cooling Effectiveness

1994 ◽  
Author(s):  
Jeffrey P. Bons ◽  
Charles D. MacArthur ◽  
Richard B. Rivir
Keyword(s):  
Film Cooling ◽  
Density Ratio ◽  
Plate Boundary ◽  
Constant Density ◽  
Freestream Turbulence ◽  
Injection Hole ◽  
Adiabatic Wall ◽  
Cooling Effectiveness ◽  
Film Cooling Effectiveness ◽  
Single Row

This study investigated the adiabatic wall cooling effectiveness of a single row of film cooling boles injecting into a turbulent flat plate boundary layer below a turbulent, zero pressure gradient freestream. Levels of freestream turbulence (Tu) up to 17.4% were generated using a method which simulates conditions at a gas turbine combustor exit. Film cooling was injected from a single row of five 35 degree slant-hole injectors (length/diameter = 3.5. pitch/diameter = 3.0) at blowing ratios from 0.55 to 1.85 and at a nearly constant density ratio (coolant density/freestream density) of 0.95. Film cooling effectiveness data is presented for Tu levels ranging from 0.9% to 17% at a constant freestream Reynolds number based on injection hole diameter of 19000. Results show that elevated levels of freestream turbulence reduce film cooling effectiveness by up to 70% in the region directly downstream of the injection hole due to enhanced mixing. At the same time, high freestream turbulence also produces a 50–100% increase in film cooling effectiveness in the region between injection boles. This is due to accelerated spanwise diffusion of the cooling fluid, which also produces an earlier merger of the coolant jets from adjacent holes.

Film Cooling With Forward and Backward Injection for Cylindrical and Fan-Shaped Holes Using PSP Measurement Technique

2014 ◽  
Author(s):  
Andrew F. Chen ◽  
Shiou-Jiuan Li ◽  
Je-Chin Han
Keyword(s):  
Film Cooling ◽  
Free Stream ◽  
Density Ratio ◽  
Cooling Effectiveness ◽  
Film Cooling Effectiveness ◽  
Free Stream Turbulence ◽  
Blowing Ratio ◽  
Cylindrical Holes ◽  
Density Ratios ◽  
Better Than

A systematic study was performed to investigate the combined effects of hole geometry, blowing ratio, density ratio and free-stream turbulence intensity on flat plate film cooling with forward and backward injection. Detailed film cooling effectiveness distributions were obtained using the steady state pressure sensitive paint (PSP) technique. Four common film-hole geometries with forward injection were used in this study: simple angled cylindrical holes and fan-shaped holes, and compound angled (β = 45°) cylindrical holes and fan-shaped holes. Additional four film-hole geometries with backward injection were tested by reversing the injection direction from forward to backward to the mainstream. There are seven holes in a row on each plate and each hole is 4 mm in diameter. The hole length to diameter ratio is 7.5. The blowing ratio effect was studied at 10 different blowing ratios ranging from M = 0.3 to M = 2.0. The coolant to main stream density ratio (DR) effect was studied by using foreign gases with DR = 1 (N2), 1.5 (CO2), and 2 (15% SF6 + 85% Ar). The free stream turbulence intensity effect was tested at 0.5% and 6%. The results show higher density coolant provides higher effectiveness than lower density coolant, fan-shaped holes perform better than cylindrical holes, and compound angled holes are better than simple angled holes. In general, the results show the film cooling effectiveness with backward injection is greatly reduced for shaped holes as compared with the forward injection. However, significant improvements can be seen in both simple angled and compound angled cylindrical holes at higher blowing ratios and density ratio (DR = 2). Comparison was made between experimental data and empirical correlations for simple angled fan-shaped holes at engine representative density ratios. An improved correlation which covers a wider range of density ratios (DR = 1.0 to DR = 2.0) is proposed.

Film Cooling Effectiveness in High-Turbulence Flow

1991 ◽  
Vol 113 (3) ◽  
pp. 479-483 ◽  
Author(s):  
G. W. Jumper ◽  
W. C. Elrod ◽  
R. B. Rivir
Keyword(s):  
Film Cooling ◽  
Free Stream ◽  
Reynolds Numbers ◽  
Cooling Effectiveness ◽  
Film Cooling Effectiveness ◽  
Single Row ◽  
Free Stream Turbulence ◽  
Cooling Flow ◽  
Turbulence Flow ◽  
High Turbulence

The mechanisms influencing film cooling effectiveness on a flat plate in high free-stream turbulence using a single row of 30 deg slant-hole injectors are examined. The primary area of focus is the area within 40 diameters downstream of injection. Of interest are blowing ratios for optimum film cooling effectiveness within 10 diameters downstream of injection, and the decay of film cooling effectiveness down the plate. Film cooling flow Reynolds numbers. Re, from 24,700 to 86,600 and free-stream turbulence intensities from 14 to 17 percent were examined. Changes in Reynolds number or free-stream turbulence broadened and increased the blowing ratios for optimum film cooling effectiveness. In comparison with tests conducted at 0.5 percent free-stream turbulence, higher free-stream turbulence causes a faster decay in film cooling effectiveness, or a reduction in the effective cooling length, and a reduction of the level of cooling effectiveness at the higher Reynolds numbers.

Turbine Vane Endwall Film Cooling From Cross-Row Configuration With Simulated Upstream Leakage Flow

2017 ◽  
Author(s):  
Nafiz H. K. Chowdhury ◽  
Chao-Cheng Shiau ◽  
Je-Chin Han ◽  
Luzeng Zhang ◽  
Hee-Koo Moon
Keyword(s):  
Film Cooling ◽  
Density Ratio ◽  
Companion Paper ◽  
Leakage Flow ◽  
Blow Down ◽  
Cooling Effectiveness ◽  
Film Cooling Effectiveness ◽  
Free Stream Turbulence ◽  
Lift Off ◽  
Endwall Cooling

The performance of a full coverage film cooling configuration called cross-row (CR) configuration including upstream inlet leakage flow was studied by measuring the adiabatic film cooling effectiveness distribution using PSP technique. Experiments were conducted in a blow-down wind tunnel cascade facility at the isentropic exit Mach number of 0.5 corresponding to inlet Reynolds number of 3.8 × 105, based on axial chord length. A free-stream turbulence level was generated as high as 19% with a length scale of 1.7 cm at the inlet. The results are presented as two-dimensional adiabatic film cooling effectiveness distributions on the endwall surface with corresponding spanwise averaged distributions. The focus of this study is to investigate the effect of coolant-to-mainstream mass flow ratio (MFR) and density ratio (DR) on the proposed endwall cooling design. Initially, increased MFR for the endwall cooling and upstream leakage levels up the local adiabatic cooling effectiveness and yields relatively uniform coverage on the entire endwall. However, in either case, highest MFR does not provide any improvement as endwall cooling suffered from the jet lift-off and leakage coolant coverage restricted by the downstream near-wall flow field. Results also indicated a density ratio of 1.5 provides the best performance. Finally, a fair comparison is made with another design called axial-row (AR) configuration from a companion paper.

Experimental Film Cooling Effectiveness of Multi-Row Patterns on Flat and Step-Down Surfaces

2019 ◽  
Author(s):  
Filippo Baldino ◽  
Mohammad E. Taslim
Keyword(s):  
Film Cooling ◽  
Density Ratio ◽  
Hole Diameter ◽  
Constant Density ◽  
Airfoil Surface ◽  
Cooling Effectiveness ◽  
Film Cooling Effectiveness ◽  
Flat Surfaces ◽  
Step Down ◽  
Turbine Airfoils

Abstract Multiple rows of film cooling holes have been widely used for the protection of gas turbine airfoils and other hot sections. In the common approach, however, the streamwise surfaces between the film holes may not receive enough protection. The objective of this research was to overcome this issue by introducing a new layout of film cooling, the step-down surfaces. Pressure-sensitive paint technique was used to test three pairs of geometries. Each pair consists of a flat and a step-down surface for back to back comparisons, under otherwise identical conditions. Two rows of 30° angled cylindrical holes of 3.175 mm diameter, exiting at the step bottom corner, introduced the coolant to the surface. Two spanwise pitch-to-diameter ratios of 2 and 4, two row distance to hole diameter of 4 and 8, four blowing ratios of 0.25, 0.5, 0.75 and 1, all at a constant density ratio of 1 were tested. Adding a step-down of the order of 0.8 hole-diameter proved to significantly increase the overall film cooling effectiveness. Two major improvements compared to a flat surfaces were observed: (a) longer streamwise film cooling effectiveness (b) more uniform spanwise distribution of coolant. The main reason of all the improvements is the aerodynamic phenomenon governing the flow evolution, the Coanda effect. The latter, indeed, enhances the flow attachment to the airfoil surface downstream the step.

Film Cooling Effectiveness for Short Film Cooling Holes Fed by a Narrow Plenum

1999 ◽  
Vol 122 (3) ◽  
pp. 553-557 ◽  
Author(s):  
C. A. Hale ◽  
M. W. Plesniak ◽  
S. Ramadhyani
Keyword(s):  
Film Cooling ◽  
Short Film ◽  
Injection Hole ◽  
Cooling Effectiveness ◽  
Cooling Performance ◽  
Film Cooling Effectiveness ◽  
Single Row ◽  
Hole Geometry ◽  
Thin Walled ◽  
Film Cooling Holes

The adiabatic, steady-state liquid crystal technique was used to measure surface adiabatic film cooling effectiveness values in the near-hole region X/D<10. A parametric study was conducted for a single row of short holes L/D⩽3 fed by a narrow plenum H/D=1. Film cooling effectiveness values are presented and compared for various L/D ratios (0.66 to 3.0), three different blowing ratios (0.5, 1.0, and 1.5), two different plenum feed configurations (co-flow and counterflow), and two different injection angles (35 and 90 deg). Injection hole geometry and plenum feed direction were found to affect short hole film cooling performance significantly. Under certain conditions, similar or improved coverage was achieved with 90 deg holes compared with 35 deg holes. This result has important implications for manufacturing of thin-walled film-cooled blades or vanes. [S0889-504X(00)00603-6]

Turbine Vane Endwall Film Cooling With Slashface Leakage and Discrete Hole Configuration

2017 ◽  
Vol 139 (6) ◽  
Author(s):  
Nafiz H. K. Chowdhury ◽  
Chao-Cheng Shiau ◽  
Je-Chin Han ◽  
Luzeng Zhang ◽  
Hee-Koo Moon
Keyword(s):  
Film Cooling ◽  
Guide Vane ◽  
Density Ratio ◽  
Secondary Flows ◽  
Blow Down ◽  
Cooling Effectiveness ◽  
Film Cooling Effectiveness ◽  
Free Stream Turbulence ◽  
Leakage Flows ◽  
Turbine Vane

Turbine vanes are typically assembled as a section containing single or double airfoil units in an annular pattern. First stage guide vane assembly results in two common mating interfaces: a gap between combustor and vane endwall and another resulted from the adjacent sections, called slashface. High pressure coolant could leak through these gaps to reduce the ingestion of hot gas and achieve certain cooling benefit. As vane endwall region flow field is already very complicated due to highly three-dimensional secondary flows, then a significant influence on endwall cooling can be expected due to the gap leakage flows. To determine the effect of leakage flows from those gaps, film cooling effectiveness distributions were measured using pressure sensitive paint (PSP) technique on the endwall of a scaled up, midrange industrial turbine vane geometry with the multiple rows of discrete film cooling (DFC) holes inside the passages. Experiments were performed in a blow-down wind tunnel cascade facility at the exit Mach number of 0.5 corresponding to Reynolds number of 3.8 × 105 based on inlet conditions and axial chord length. Passive turbulence grid was used to generate free-stream turbulence (FST) level about 19% with an integral length scale of 1.7 cm. Two parameters, coolant-to-mainstream mass flow ratio (MFR) and density ratio (DR), were studied. The results are presented as two-dimensional film cooling effectiveness distribution on the vane endwall surface with the corresponding spanwise averaged values along the axial direction.

Film Cooling Effectiveness Distributions on a Flat Plate With a Double Hole Geometry Using PSP

2011 ◽  
Author(s):  
Lesley M. Wright ◽  
Evan L. Martin
Keyword(s):  
Flat Plate ◽  
Film Cooling ◽  
Surface Film ◽  
Density Ratio ◽  
Cooling Effectiveness ◽  
Freestream Velocity ◽  
Film Cooling Effectiveness ◽  
Single Row ◽  
Blowing Ratio ◽  
Hole Geometry

Detailed film cooling effectiveness distributions are obtained on a flat plate using the pressure sensitive paint (PSP) technique. The effects of average blowing ratio (M = 0.25–1.0) and coolant – to – mainstream density ratio (DR = 1.0–1.4) are evaluated in a low speed wind tunnel with a freestream velocity of 8.5 m/s and a freestream turbulence intensity of 6.8%. The coolant – to – mainstream density ratio is varied by using either nitrogen (DR = 1.0) or argon (DR = 1.4) as the coolant gases. The double hole geometry consists of a row of simple angle (θ = 35°), cylindrical holes coupled with one row of compound angle holes (θ = 45°, β = 50°). With the selected geometry, the compound holes effectively weaken the counter rotating vortex pair formed within the traditional simple angle hole. Therefore, the surface film cooling effectiveness is increased compared to a single row of simple angle film cooling holes. While increasing the blowing ratio decreases the film cooling effectiveness, the severity of the film cooling effectiveness reduction is less than with the single row of holes.

Evaluation of Two-Equation Models of Turbulence in Predicting Film Cooling Performance Under High Free Stream Turbulence

2007 ◽  
Author(s):  
Savas Yavuzkurt ◽  
Jawad S. Hassan
Keyword(s):  
Film Cooling ◽  
Free Stream ◽  
Turbulence Models ◽  
Accurate Solution ◽  
Diameter Ratio ◽  
Tube Length ◽  
Cooling Effectiveness ◽  
Film Cooling Effectiveness ◽  
Free Stream Turbulence ◽  
Density Ratios

The capabilities of four two-equation turbulence models in predicting film cooling effectiveness under high free stream turbulence (FST) intensity (Tu = 10%) were investigated and their performance are presented and discussed. The four turbulence models are: the standard k-ε, RNG, and realizable k-ε models as well as the standard k-ω model all four found in the FLUENT CFD code. In all models, the enhanced wall treatment has been used to resolve the flow near solid boundaries. A systematic approach has been followed in the computational setup to insure grid-independence and accurate solution that reflects the true capabilities of these models. Exact geometrical and flow-field replicas of an experimental study on discrete hole film cooling were generated and used in FLUENT. A pitch-to-diameter ratio of 3.04, injection tube length-to-diameter ratio of 4.6 and density ratios of 0.92 and 0.97 were some of the parameters used in the film cooling analysis. The study covered two levels of blowing ratios (M = 0.5 and 1.5) at an environment of what is defined as high initial free-stream turbulence intensity (Tu = 10%). Performance of these models under a very low initial FST were presented in a paper by the authors in Turbo Expo 2006. In that case, the standard k-ε model had the most consistent performance among all considered turbulence models and the best centerline film cooling effectiveness predictions under very low FST. However, after the addition of high FST in the free-stream, even the standard k-ε model started to deviate greatly from the experimental data (up to 200% over-prediction) under high blowing ratios (M = 1.5). The model which performed the best under high FST but low blowing ratios (M = 0.5) is still the standard k-ε model. In all cases only standard k-ε model results match the trends of data for both cases. It can be said that under high FST with high M all the models do not do a good job of predicting the data. It was concluded that these deviations resulted from the effects of both high FST and high M. Under high M, near the injection holes deviations could result from the limitations of Boussinesq hypothesis relating the direction of Reynolds stress to the mean strain rate. Also, it seems like all models have trouble including the effects of high FST by not being able to take into account high levels of diffusion of turbulence from the free stream. However, standard k-ε model still looks like the best candidate for further improvement with the addition of new diffusion model for TKE under high FST.

Film Cooling Effectiveness for Injection from Multirow Holes

1979 ◽  
Vol 101 (1) ◽  
pp. 101-108 ◽  
Author(s):  
M. Sasaki ◽  
K. Takahara ◽  
T. Kumagai ◽  
M. Hamano
Keyword(s):  
Pressure Gradient ◽  
Wall Temperature ◽  
Film Cooling ◽  
Infrared Camera ◽  
Superposition Model ◽  
Adiabatic Wall ◽  
Cooling Effectiveness ◽  
Film Cooling Effectiveness ◽  
Single Row ◽  
Temperature Distributions

Experimental results are presented for film cooling effectiveness with injection from both a single row and multiple rows of holes with spanwise hole-to-hole spacings of three hole diameters. In the multi-row cases, the injection holes were arranged in staggered patterns with streamwise row-to-row spacings of five or ten hole diameters. Adiabatic wall temperature distributions near and downstream of injection holes were well visualized using a scanning infrared camera. The effect of mainstream pressure gradient was partially included. The additive nature of multi-row film cooling was demonstrated experimentally, in agreement with the Sellers superposition model.

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