Measurement of Eddy Diffusivity of Momentum in Film Cooling Flows With Streamwise Injection

1999 ◽  
Vol 122 (1) ◽  
pp. 178-183 ◽  
Author(s):  
R. W. Kaszeta ◽  
T. W. Simon
Keyword(s):  
Film Cooling ◽  
Density Ratio ◽  
Flux Ratio ◽  
Eddy Diffusivity ◽  
Turbulent Shear ◽  
Spanwise Direction ◽  
Intensity Level ◽  
Mean Velocity ◽  
Injection Angle ◽  
Free Stream Turbulence

Measurement of mean velocity and turbulent shear stress are presented for the mixing region of a film cooling situation in which the coolant is streamwise injected with an injection angle of 35 deg. Measurements are performed using triple-sensor anemometry so that all three instantaneous velocity components are documented. The free-stream turbulence intensity level is 12 percent, the ratio of the integral length scale to injection hole diameter is 4.0, the coolant-to-mainstream momentum flux ratio is 1.0, and the density ratio is unity. From these measurements, values for the eddy diffusivities of momentum in the lateral and wall-normal directions are calculated. Additionally, calculated values of the ratio of eddy diffusivity in the spanwise direction to eddy diffusivity in the wall-normal direction are presented, which provide documentation of the anisotropy of turbulent transport in this film cooling flow. [S0889-504X(00)02001-8]

scholarly journals Measurement of Eddy Diffusivity of Momentum in Film Cooling Flows With Streamwise Injection

1999 ◽  
Author(s):  
Richard W. Kaszeta ◽  
Terrence W. Simon
Keyword(s):  
Film Cooling ◽  
Turbulent Transport ◽  
Density Ratio ◽  
Flux Ratio ◽  
Eddy Diffusivity ◽  
Turbulent Shear ◽  
Spanwise Direction ◽  
Intensity Level ◽  
Mean Velocity ◽  
Injection Angle

Measurements of mean velocity and turbulent shear stress are presented for the mixing region of a film cooling situation in which the coolant is streamwise injected with an injection angle of 35°. Measurements are performed using triple-sensor anemometry so that all three instantaneous velocity components are documented. The freestream turbulence intensity level is 12%, the ratio of the integral length scale to injection hole diameter is 4.0, the coolant-to-mainstream momentum flux ratio is 1.0, and the density ratio is unity. From these measurements, values for the eddy diffusivities of momentum in the lateral and wall-normal directions are calculated. Additionally, calculated values of the ratio of eddy diffusivity in the spanwise direction to eddy diffusivity in the wall-normal direction are presented, which provide documentation of the anisotropy of turbulent transport in this film cooling flow.

Adiabatic Effectiveness, Thermal Fields, and Velocity Fields for Film Cooling With Large Angle Injection

1997 ◽  
Vol 119 (2) ◽  
pp. 352-358 ◽  
Author(s):  
A. Kohli ◽  
D. G. Bogard
Keyword(s):  
Film Cooling ◽  
Momentum Flux ◽  
Thermal Field ◽  
Density Ratio ◽  
Large Angle ◽  
Flux Ratio ◽  
Cryogenic Cooling ◽  
Round Hole ◽  
Mean Velocity ◽  
Injection Angle

The film cooling performance and velocity field were investigated for discrete round holes inclined at an injection angle of 55 deg. Results are compared to typical round film cooling holes, with an injection angle of 35 deg. All experiments in this study were performed at a density ratio of DR = 1.6, using cryogenic cooling of the injected air. Centerline and lateral distributions of effectiveness were obtained for a range of momentum flux ratios. Thermal field and two component mean velocity and turbulence intensity measurements were made at a momentum flux ratio that was within the range of maximum spatially averaged effectiveness. Compared to round holes with 35 deg injection angle, the 55 deg holes showed only a slight degradation in centerline effectiveness for low momentum flux ratios, while a significant reduction in effectiveness was seen at high momentum flux ratios. The thermal field for the 55 deg round holes indicated a faster decay of cooling capacity for the 55 deg round holes. The high turbulence levels for the 55 deg round hole coincided with the sharp velocity gradients between the jet and free stream, and the decay of turbulence levels with downstream distance was found to be similar to those for a 35 deg hole.

scholarly journals Adiabatic Effectiveness, Thermal Fields, and Velocity Fields for Film Cooling With Large Angle Injection

1995 ◽  
Author(s):  
Atul Kohli ◽  
David G. Bogard
Keyword(s):  
Film Cooling ◽  
Momentum Flux ◽  
Thermal Field ◽  
Density Ratio ◽  
Large Angle ◽  
Flux Ratio ◽  
Cryogenic Cooling ◽  
Round Hole ◽  
Mean Velocity ◽  
Injection Angle

The film cooling performance and velocity field were investigated for discrete round holes inclined at an injection angle of 55°. Results are compared to typical round film cooling holes, with an injection angle of 35°. All experiments in this study were performed at a density ratio of DR = 1.6, using cryogenic cooling of the injected air. Centerline and lateral distributions of effectiveness, were obtained for a range of momentum flux ratios. Thermal field and two component mean velocity and turbulence intensity measurements were made at a momentum flux ratio which was within the range of maximum spatially averaged effectiveness. Compared to round holes with 35° injection angle, the 55° holes showed only a slight degradation in centerline effectiveness for low momentum flux ratios, while a significant reduction in effectiveness was seen at high momentum flux ratios. The thermal field for the 55° round holes indicated a faster decay of cooling capacity for the 55° round holes. The high turbulence levels for the 55° round hole coincided with the sharp velocity gradients between the jet and freestream, and the decay of turbulence levels with downstream distance was found to be similar to those for a 35° hole.

scholarly journals Film Cooling From Spanwise Oriented Holes in Two Staggered Rows

1995 ◽  
Author(s):  
Phillip M. Ligrani ◽  
Anthony E. Ramsey
Keyword(s):  
Film Cooling ◽  
Density Ratio ◽  
Flux Ratio ◽  
Test Surface ◽  
Spanwise Direction ◽  
Transfer Coefficients ◽  
Blowing Ratio ◽  
Streamwise Location ◽  
Adiabatic Effectiveness ◽  
Lift Off

Adiabatic effectiveness and iso-energetic heat transfer coefficients are presented from measurements downstream of film-cooling holes inclined at 30 degrees with respect to the test surface in spanwise/normal planes. With this configuration, holes are spaced 3d apart in the spanwise direction and 4d in the streamwise direction in two staggered rows. Results are presented for an injectant to freestream density ratio near 1.0, and injection blowing ratios from 0.5 to 1.5. Spanwise-averaged adiabatic effectiveness values downstream of the spanwise/normal plane holes are significantly higher than values measured downstream of simple angle holes for x/d<25–70 (depending on blowing ratio) when compared for the same normalized streamwise location, blowing ratio, and spanwise and streamwise hole spacings. Differences are principally due to different coalescence of injectant accumulations from the two different rows of holes, as well as significantly different lift-off dependence on momentum flux ratio. Spanwise-averaged iso-energetic Stanton number ratios are somewhat higher than ones measured downstream of other simple and compound angle configurations studied. Values range between 1.0 and 1.41, increase with blowing ratio at each streamwise station, and show little variation with streamwise location for each value of blowing ratio tested.

Scaling of Performance for Varying Density Ratio Coolants on an Airfoil With Strong Curvature and Pressure Gradient Effects

2000 ◽  
Author(s):  
Marcia I. Ethridge ◽  
J. Michael Cutbirth ◽  
David G. Bogard
Keyword(s):  
Pressure Gradient ◽  
Film Cooling ◽  
Density Ratio ◽  
Flux Ratio ◽  
Leading Edge ◽  
Suction Side ◽  
Cooling Performance ◽  
Injection Angle ◽  
Adiabatic Effectiveness ◽  
Strong Curvature

An experimental study was conducted to investigate the film cooling performance on the suction side of a first stage turbine vane. Tests were conducted on a nine times scale vane model at density ratios of DR = 1.1 and 1.6 over a range of blowing conditions, 0.2 ≤ M ≤ 1.5 and 0.05 ≤ I ≤ 1.2. Two different mainstream turbulence intensity levels, Tu∞ = 0.5% and 20%, were also investigated. The row of coolant holes studied was located in a position of both strong curvature and strong favorable pressure gradient. In addition, its performance was isolated by blocking the leading edge showerhead coolant holes. Adiabatic effectiveness measurements were made using an infrared camera to map the surface temperature distribution. The results indicate that film cooling performance was greatly enhanced over holes with a similar 50° injection angle on a flat plate. Overall, adiabatic effectiveness scaled with mass flux ratio for low blowing conditions and with momentum flux ratio for high blowing conditions. However, for M < 0.5 there was a higher rate of decay for the low density ratio data. High mainstream turbulence had little effect at low blowing ratios, but degraded performance at higher blowing ratios.

Effects of Density Ratio on the Hydrodynamics of Film Cooling

1990 ◽  
Vol 112 (3) ◽  
pp. 437-443 ◽  
Author(s):  
J. R. Pietrzyk ◽  
D. G. Bogard ◽  
M. E. Crawford
Keyword(s):  
Flow Field ◽  
Film Cooling ◽  
Free Stream ◽  
Laser Doppler Anemometry ◽  
Density Ratio ◽  
Vertical Plane ◽  
Flux Ratio ◽  
Mean Velocity ◽  
Entire Flow ◽  
Hydrodynamic Study

This paper presents the results of a detailed hydrodynamic study of a row of inclined jets issuing into a crossflow with a density ratio of injectant to free stream of 2. Laser-Doppler anemometry was used to measure the vertical and streamwise components of velocity for a jet-to-free stream mass flux ratio of 0.5. Mean velocity components and turbulent Reynolds normal and shear stress components were measured at locations in a vertical plane along the centerline of the jet from 1 diameter upstream to 30 diameters downstream of the jet. The results, which have application to film cooling, give a quantitative picture of the entire flow field, from the approaching flow upstream of the jet, through the interaction region of the jet and free stream, to the relaxation region downstream where the flow field approaches that of a standard turbulent boundary layer.

A Systematic Computational Methodology Applied to a Three-Dimensional Film-Cooling Flowfield

1997 ◽  
Vol 119 (4) ◽  
pp. 777-785 ◽  
Author(s):  
D. K. Walters ◽  
J. H. Leylek
Keyword(s):  
Film Cooling ◽  
Gas Turbines ◽  
Turbulence Modeling ◽  
Density Ratio ◽  
Three Dimensional ◽  
Elliptic Solution ◽  
Injection Angle ◽  
Free Stream Turbulence ◽  
Acceleration Techniques ◽  
Computational Methodology

Numerical results are presented for a three-dimensional discrete-jet in crossflow problem typical of a realistic film-cooling application in gas turbines. Key aspects of the study include: (1) application of a systematic computational methodology that stresses accurate computational model of the physical problem, including simultaneous, fully elliptic solution of the crossflow, film-hole, and plenum regions; high-quality three-dimensional unstructured grid generation techniques, which have yet to be documented for this class of problems; the use of a high-order discretization scheme to reduce numerical errors significantly; and effective turbulence modeling; (2) a three-way comparison of results to both code validation quality experimental data and a previously documented structured grid simulation; and (3) identification of sources of discrepancy between predicted and measured results, as well as recommendations to alleviate these discrepancies. Solutions were obtained with a multiblock, unstructured/adaptive grid, fully explicit, time-marching, Reynolds-averaged Navier–Stokes code with multigrid, local time stepping, and residual smoothing type acceleration techniques. The computational methodology was applied to the validation test case of a row of discrete jets on a flat plate with a streamwise injection angle of 35 deg, and two film-hole length-to-diameter ratios of 3.5 and 1.75. The density ratio for all cases was 2.0, blowing ratio was varied from 0.5 to 2.0, and free-stream turbulence intensity was 2 percent. The results demonstrate that the prescribed computational methodology yields consistently more accurate solutions for this class of problems than previous attempts published in the open literature. Sources of disagreement between measured and computed results have been identified, and recommendations made for future prediction of film-cooling problems.

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.

Scaling of Performance for Varying Density Ratio Coolants on an Airfoil With Strong Curvature and Pressure Gradient Effects

2000 ◽  
Vol 123 (2) ◽  
pp. 231-237 ◽  
Author(s):  
Marcia I. Ethridge ◽  
J. Michael Cutbirth ◽  
David G. Bogard
Keyword(s):  
Pressure Gradient ◽  
Film Cooling ◽  
Density Ratio ◽  
Flux Ratio ◽  
Leading Edge ◽  
Suction Side ◽  
Cooling Performance ◽  
Injection Angle ◽  
Adiabatic Effectiveness ◽  
Strong Curvature

An experimental study was conducted to investigate the film cooling performance on the suction side of a first-stage turbine vane. Tests were conducted on a nine times scale vane model at density ratios of DR=1.1 and 1.6 over a range of blowing conditions, 0.2⩽M⩽1.5 and 0.05⩽I⩽1.2. Two different mainstream turbulence intensity levels, Tu∞=0.5 and 20 percent, were also investigated. The row of coolant holes studied was located in a position of both strong curvature and strong favorable pressure gradient. In addition, its performance was isolated by blocking the leading edge showerhead coolant holes. Adiabatic effectiveness measurements were made using an infrared camera to map the surface temperature distribution. The results indicate that film cooling performance was greatly enhanced over holes with a similar 50 deg injection angle on a flat plate. Overall, adiabatic effectiveness scaled with mass flux ratio for low blowing conditions and with momentum flux ratio for high blowing conditions. However, for M<0.5, there was a higher rate of decay for the low density ratio data. High mainstream turbulence had little effect at low blowing ratios, but degraded performance at higher blowing ratios.

A Systematic Computational Methodology Applied to a Three–Dimensional Film–Cooling Flowfield

1996 ◽  
Author(s):  
Dibbon K. Walters ◽  
James H. Leylek
Keyword(s):  
Film Cooling ◽  
Gas Turbines ◽  
Density Ratio ◽  
Three Dimensional ◽  
Test Case ◽  
Elliptic Solution ◽  
Injection Angle ◽  
Free Stream Turbulence ◽  
Acceleration Techniques ◽  
Computational Methodology

Numerical results are presented for a three–dimensional discrete–jet in crossflow problem typical of a realistic film–cooling application in gas turbines. Key aspects of the study include: (1) Application of a systematic computational methodology that stresses accurate computational model of the physical problem, including simultaneous, fully–elliptic solution of the crossflow, film–hole, and plenum regions; high quality 3–D unstructured grid generation techniques which have yet to be documented for this class of problems; the use of a high order discretization scheme to significantly reduce numerical errors; and effective turbulence modelling; (2) A three–way comparison of results to both code validation quality experimental data and a previously documented structured grid simulation; and (3) Identification of sources of discrepancy between predicted and measured results, as well as recommendations to alleviate these discrepancies. Solutions were obtained with a multi–block, unstructured/adaptive grid, fully explicit, time–marching, Reynolds averaged Navier–Stokes code with multi-grid, local time stepping, and residual smoothing type acceleration techniques. The computational methodology was applied to the validation test case of a row of discrete jets on a flat plate with a streamwise injection angle of 35°, and two film–hole length–to–diameter ratios of 3.5 and 1.75. The density ratio for all cases was 2.0, blowing ratio was varied from 0.5 to 2.0, and free–stream turbulence intensity was 2%. The results demonstrate that the prescribed computational methodology yields consistently more accurate solutions for this class of problems than previous attempts published in the open literature. Sources of disagreement between measured and computed results have been identified, and recommendations made for future prediction of this class of problems.

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