Effects of Very High Free-Stream Turbulence on the Jet–Mainstream Interaction in a Film Cooling Flow

1998 ◽  
Vol 120 (4) ◽  
pp. 785-790 ◽  
Author(s):  
A. Kohli ◽  
D. G. Bogard
Keyword(s):  
High Frequency ◽  
Film Cooling ◽  
Thermal Field ◽  
Free Stream ◽  
Complex Interaction ◽  
Free Stream Turbulence ◽  
High Frequency Response ◽  
Cooling Flow ◽  
The Mean ◽  
Very High

Dispersion of coolant jets in a film cooling flow field is the result of a highly complex interaction between the film cooling jets and the mainstream. Understanding this complex interaction, particularly near the injection location, is critical for improving the predictive capabilities of existing film cooling models, especially when very high free-stream turbulence levels exist. This study uses a high-Frequency-response temperature sensor to investigate the mean and fluctuating thermal field of a film cooling flow for two vastly different free-stream turbulence levels (0.5 and 20 percent). The high-frequency-response temperature sensor provides new information about the film cooling flow in terms of actual rms levels (Θ′), probability density functions (pdf’s), and frequency spectra of the thermal field. Results are presented for both free-stream conditions using round hosed inclined at 35 deg, at a momentum flux ration of I = 0.156 and density ratio of DR = 1.05. The mean thermal field results show severe degradation of the film cooling jet occurs with very high free-stream turbulence levels. Temperature rms results indicate levels as high as Θ′ = 0.25 exist at the jet-mainstream interface. More information is provided by the temperature pdf’s, which are able to identify differences in the jet-mainstream interaction for the two free stream conditions. With small free-stream turbulence, strong intermittent flow structures generated at the jet-mainstream interface disperse the jet by moving hot main stream fluid into the coolant core, and ejecting coolant fluid into the mainstream. When the free stream has large scales and very high turbulence levels, the jet-mainstream interface is obliterated by large-scale turbulent structures originating from the free stream, which completely penetrate the coolant jet, causing very rapid dispersion of the film cooling jet.

scholarly journals Effects of Very High Free-Stream Turbulence on the Jet-Mainstream Interaction in a Film Cooling Flow

1997 ◽  
Author(s):  
Atul Kohli ◽  
David G. Bogard
Keyword(s):  
High Frequency ◽  
Film Cooling ◽  
Thermal Field ◽  
Free Stream ◽  
Complex Interaction ◽  
Free Stream Turbulence ◽  
High Frequency Response ◽  
Cooling Flow ◽  
The Mean ◽  
Very High

Dispersion of coolant jets in a film cooling flow field is the result of a highly complex interaction between the film cooling jets and the mainstream. Understanding this complex interaction, particularly near the injection location, is critical for improving the predictive capabilities of existing film cooling models, especially when very high free-stream turbulence levels exist. This study uses a high frequency response temperature sensor to investigate the mean and fluctuating thermal field of a film cooling flow for two vastly different free-stream turbulence levels (0.5% and 20%). The high frequency response temperature sensor provides new information about the film cooling flow in terms of actual rms levels (Θ′), probability density functions (pdf’s), and frequency spectra of the thermal field. Results are presented for both free-stream conditions using round holes inclined at 35°, at a momentum flux ratio of I = 0.156 and density ratio of DR = 1.05. The mean thermal field results show severe degradation of the film cooling jet occurs with very high free-stream turbulence levels. Temperature rms results indicate levels as high as Θ′ = 0.25 exist at the jet-mainstream interface. More information is provided by the temperature pdf’s which are able to identify differences in the jet-mainstream interaction for the two free-stream conditions. With small free-stream turbulence, strong intermittent flow structures generated at the jet-mainstream interface disperse the jet by moving hot mainstream fluid into the coolant core, and ejecting coolant fluid into the mainstream. When the free-stream has large scales and very high turbulence levels, the jet-mainstream interface is obliterated by large scale turbulent structures originating from the free-stream which completely penetrate the coolant jet causing very rapid dispersion of the film cooling jet.

Fluctuating Thermal Field in the Near-Hole Region for Film Cooling Flows

1998 ◽  
Vol 120 (1) ◽  
pp. 86-91 ◽  
Author(s):  
A. Kohli ◽  
D. G. Bogard
Keyword(s):  
Probability Density ◽  
Film Cooling ◽  
Thermal Field ◽  
Density Ratio ◽  
Flux Ratio ◽  
Probability Density Functions ◽  
Intermittent Flow ◽  
Density Functions ◽  
High Frequency Response ◽  
Cooling Flow

The film cooling flow field is the result of a highly complex interaction between the film cooling jets and the mainstream. Understanding this interaction is important in order to explain the physical mechanisms involved in the rapid decrease of effectiveness, which occurs close to the hole exit. Not surprisingly, it is this region that is not modeled satisfactorily with current film cooling models. This study uses a high-frequency-response temperature sensor, which provides new information about the film cooling flow in terms of actual turbulence levels and probability density functions of the thermal field. Mean and rms temperature results are presented for 35 deg round holes at a momentum flux ratio of I = 0.16, at a density ratio of DR = 1.05. Probability density functions of the temperature indicate penetration of the mainstream into the coolant core, and ejection of coolant into the mainstream. Extreme excursions in the fluctuating temperature measurements suggest existence of strong intermittent flow structures responsible for dilution and dispersion of the coolant jets.

PIV Measurements of Periodically Forced Flat Plate Film Cooling Flows With High Free Stream Turbulence

1996 ◽  
Author(s):  
Sivaram P. Gogineni ◽  
Darryl D. Trump ◽  
Richard B. Rivir ◽  
David J. Pestian
Keyword(s):  
Film Cooling ◽  
Free Stream ◽  
Near Field ◽  
Piv Measurements ◽  
Free Stream Turbulence ◽  
Cooling Flows ◽  
Cooling Flow ◽  
Reduced Frequency ◽  
Image Velocimetry ◽  
Cooling Hole

Two color double pulsed Particle Image Velocimetry (PIV) measurements of simulated turbine film cooling flows have been made for blowing ratios of 0.5, 0.7, and 1.0 in the near field of the film cooling hole, x/d≤2.5. The effect of the vane wake on the rotor film cooling flow is simulated by periodically forcing the film cooling flows at the nnn dimensional reduced frequency. Phase locked measurements at 45 deg. increments of the periodic film forcing (0, 45, 90, 135, 180, 225, 270, and 315 deg.) for free stream turbulence levels of 1 and 17% have been made. The effects of reduced frequencies of 20 and 80, at free stream turbulence levels of 1 and 17% on the spreading of the film cooling jet are investigated. Increases in the jet spread with forcing and free stream turbulence are > 2 times those in the unforced 1% free stream turbulence case.

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.

Fluctuating Thermal Field in the Near Hole Region for Film Cooling Flows

1996 ◽  
Author(s):  
Atul Kohli ◽  
David G. Bogard
Keyword(s):  
Probability Density ◽  
Film Cooling ◽  
Thermal Field ◽  
Density Ratio ◽  
Flux Ratio ◽  
Probability Density Functions ◽  
Intermittent Flow ◽  
Density Functions ◽  
High Frequency Response ◽  
Cooling Flow

The film cooling flow field is the result of a highly complex interaction between the film cooling jets and the mainstream, Understanding this interaction is important in order to explain the physical mechanisms involved in the rapid decrease of effectiveness which occurs close to the hole exit. Not surprisingly, it is this region which is not modeled satisfactorily with current film cooling models. This study uses a high frequency response temperature sensor which provides new information about the film cooling flow in terms of actual turbulence levels and probability density functions of the thermal field. Mean and rms temperature results are presented for 35° round holes at a momentum flux ratio of I = 0.16, at a density ratio of DR = 1.05. Probability density functions of the temperature indicate penetration of the mainstream into the coolant core, and ejection of coolant into the mainstream. Extreme excursions in the fluctuating temperature measurements suggests existence of strong intermittent flow structures responsible for dilution and dispersion of the coolant jets.

Effusion-Cooling Performance at Gas Turbine Combustor Representative Flow Conditions

2012 ◽  
Author(s):  
Vinod U. Kakade ◽  
Steven J. Thorpe ◽  
Miklós Gerendás
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Film Cooling ◽  
Free Stream ◽  
Flow Conditions ◽  
Cooling Performance ◽  
Free Stream Turbulence ◽  
High Turbulence ◽  
Adiabatic Effectiveness

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.

Implicit LES for Shaped-Hole Film Cooling Flow

2017 ◽  
Author(s):  
Todd A. Oliver ◽  
Joshua B. Anderson ◽  
David G. Bogard ◽  
Robert D. Moser ◽  
Gregory Laskowski
Keyword(s):  
Film Cooling ◽  
Density Ratio ◽  
Vortex Pair ◽  
Cooling Flow ◽  
Blowing Ratio ◽  
Eddy Simulation ◽  
Mean Temperature ◽  
Cooling Hole ◽  
The Mean ◽  
Adiabatic Effectiveness

Results of a recent joint experimental and computational investigation of the flow through a plenum-fed 7-7-7 shaped film cooling hole are presented. In particular, we compare the measured adiabatic effectiveness and mean temperature against implicit large eddy simulation (iLES) for blowing ratio approximately 2, density ratio 1.6, and Reynolds number 6000. The results overall show reasonable agreement between the iLES and the experimental results for the adiabatic effectiveness and gross features of the mean temperature field. Notable discrepancies include the centerline adiabatic effectiveness near the hole, where the iLES under-predicts the measurements by Δη ≈ 0.05, and the near-wall temperature, where the simulation results show features not present in the measurements. After showing this comparison, the iLES results are used to examine features that were not measured in the experiments, including the in-hole flow and the dominant fluxes in the mean internal energy equation downstream of the hole. Key findings include that the flow near the entrance to the hole is highly turbulent and that there is a large region of backflow near the exit of the hole. Further, the well-known counter-rotating vortex pair downstream of the hole is observed. Finally, the typical gradient diffusion hypothesis for the Reynolds heat flux is evaluated and found to be incorrect.

Experimental Study of Interactions of Shock Wave With Free-Stream Turbulence

1994 ◽  
Vol 116 (4) ◽  
pp. 763-769 ◽  
Author(s):  
A. Honkan ◽  
C. B. Watkins ◽  
J. Andreopoulos
Keyword(s):  
Shock Wave ◽  
Free Stream ◽  
Length Scale ◽  
Pressure Transducers ◽  
Free Stream Turbulence ◽  
High Frequency Response ◽  
Reflected Shock ◽  
Response Pressure ◽  
Decaying Turbulence ◽  
Large Eddies

Phenomena related to turbulence interactions with shock waves have been studied in detail. The present investigation is focused on interactions of a normal shock wave with homogeneous/grid-generated turbulence. When a shock wave formed in a shock-tube is passed through a grid, the induced flow behind the shock has the features of a compressible flow with free-stream turbulence. The decaying turbulence is subjected to an interaction with the reflected shock traveling in the opposite direction. Data were sampled simultaneously from four channels of high frequency response pressure transducers and dual hot-wires probes. A cold-wire was used to provide instantaneous total temperature measurements while a single hot-wire provided instantaneous mass flux measurements. Amplification of velocity and temperature fluctuations and dissipative length scales has been found in all experiments. Velocity fluctuations of large eddies are amplified more than the fluctuations of small eddies. The dissipative length scale, however, of the large eddies is amplified less than the length scale of the small eddies.

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