Influence of Gap Leakage Downstream of the Injection Holes on Film Cooling Performance

1998 ◽  
Vol 120 (3) ◽  
pp. 541-548 ◽  
Author(s):  
Y. Yu ◽  
M. K. Chyu
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Film Cooling ◽  
Cooling System ◽  
Convective Transport ◽  
Hole Injection ◽  
Thermochromic Liquid Crystal ◽  
Cooling Performance ◽  
Temperature Problem

This study investigated a practical but never exploited issue concerning the influence of flow leakage through a gap downstream on the film cooling performance with discrete-hole injection. A heat transfer system as such can be categorized as either a three-temperature or a four-temperature problem, depending on the direction of leakage through the gap. To characterize a three-temperature-based film cooling system fully requires knowledge of both local film effectiveness and heat transfer coefficient. A second film effectiveness is necessary for characterizing a four-temperature problem. All these variables can be experimentally determined, based on the transient method of thermochromic liquid crystal imaging. Although the overall convective transport in the region is expected to be dependent on the blowing ratios of the coolants, the mass flow ratio of the two injectants, and the geometry, the current results indicated that the extent of flow injection or extraction through the gap has significant effects on the film effectiveness and less on the heat transfer coefficient, which is primarily dominated by the geometric disturbance of gap presence.

Influence of a Leaking Gap Downstream of the Injection Holes on Film Cooling Performance

1996 ◽  
Author(s):  
Y. Yu ◽  
M. K. Chyu
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Film Cooling ◽  
Cooling System ◽  
Convective Transport ◽  
Hole Injection ◽  
Thermochromic Liquid Crystal ◽  
Cooling Performance ◽  
Temperature Problem

This study investigated a practical but never exploited issue concerning the influence of flow leakage through a gap downstream on the film cooling performance with a row of discrete-hole injection. A heat transfer system as such can be categorized as either a three-temperature or a four-temperature problem, depending on the direction of leakage through the gap. To fully characterize a three-temperature based film-cooling system requires knowledge of both local film effectiveness and heat transfer coefficient. A second film effectiveness is necessary for characterizing a four-temperature problem. All these variables can be experimentally determined, based on the transient method of thermochromic liquid crystal imaging. Although the overall convective transport in the region is expected to be dependent on the blowing ratios of the coolants, the mass flow ratio of the two injectants, and the geometry, the current results indicated that the extent of flow injection or extraction through the gap has significant effects on the film effectiveness and less on the heat transfer coefficient which is primarily dominated by the geometric disturbance of gap presence.

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.

Investigations on the Influence of Rib Orientation Angle on Film Cooling Performance of Compound Holes

2018 ◽  
Author(s):  
Lin Ye ◽  
Cun-liang Liu ◽  
Hai-yong Liu ◽  
Hui-ren Zhu ◽  
Jian-xia Luo
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Film Cooling ◽  
Discharge Coefficient ◽  
Orientation Angle ◽  
Cooling Effectiveness ◽  
Cooling Performance ◽  
Film Cooling Effectiveness ◽  
Blowing Ratio

To investigate the effects of the inclined ribs on internal flow structure in film hole and the film cooling performance on outer surface, experimental and numerical studies are conducted on the effects of rib orientation angle on film cooling of compound cylindrical holes. Three coolant channel cases, including two ribbed cross-flow channels (135° and 45° angled ribs) and the plenum case, are studied under three blowing ratios (0.5, 1.0 and 2.0). 2D contours of film cooling effectiveness as well as heat transfer coefficient were measured by transient liquid crystal measurement technique (TLC). The steady RANS simulations with realizable k-ε turbulence model and enhanced wall treatment were performed. The results show that the spanwise width of film coverage is greatly influenced by the rib orientation angle. The spanwise width of the 45° rib case is obviously larger than that of the 135° rib case under lower blowing ratios. When the blowing ratio is 1.0, the area-averaged cooling effectiveness of the 135° rib case and the 45° rib case are higher than that of the plenum case by 38% and 107%, respectively. With the increase of blowing ratio, the film coverage difference between different rib orientation cases becomes smaller. The 45° rib case also produces higher heat transfer coefficient, which is higher than the 135° rib case by 3.4–8.7% within the studied blowing ratio range. Furthermore, the discharge coefficient of the 45° rib case is the lowest among the three cases. The helical motion of coolant flow is observed in the hole of 45° rib case. The jet divides into two parts after being blown out of the hole due to this motion, which induces strong velocity separation and loss. For the 135° rib case, the vortex in the upper half region of the secondary-flow channel rotates in the same direction with the hole inclination direction, which leads to the straight streamlines and thus results in lower loss and higher discharge coefficient.

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

1996 ◽  
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.

Heat Transfer Characteristics of an Impingement Plate Used in a Turbine Vane Cooling System

2001 ◽  
Author(s):  
Changmin Son ◽  
David Gillespie ◽  
Peter Ireland ◽  
Geoffrey M. Dailey
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Cooling System ◽  
Target Surface ◽  
Thermochromic Liquid Crystal ◽  
Impingement Cooling ◽  
Impingement Plate ◽  
Turbine Vane ◽  
Surface Heat Transfer Coefficient

Detailed heat transfer coefficient distributions have been measured on both surfaces of the impingement plate of an engine-representative impingement cooling system using the thermochromic liquid crystal (TLC) transient technique. The color images of the TLC on the impingement downstream surface provide evidence of a re-impingement flow. The re-impingement flow is found to contribute to local increases in the heat transfer on the impingement plate downstream surface. It was found that the average heat transfer coefficient on the impingement downstream surface is about 50% of the average target surface heat transfer coefficient. The results are compared with a previously reported correlation.

Film Cooling Performance of Waist-Shaped Slot Holes

2010 ◽  
Author(s):  
Cun-liang Liu ◽  
Hui-ren Zhu ◽  
Jiang-tao Bai ◽  
Du-chun Xu
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Film Cooling ◽  
Thermal Protection ◽  
Upstream Region ◽  
Cooling Effectiveness ◽  
Cooling Performance ◽  
Shaped Hole ◽  
The Heat Transfer Coefficient

Film cooling performance of a new shaped hole: waist-shaped slot hole is studied in this paper. Experimental measurement and numerical simulation are carried out to investigate the film cooling character and physics of this new shaped hole. And comparisons between the waist-shaped slot hole and two kinds of console holes are also performed. Both the cooling effectiveness distribution and the heat transfer coefficient distribution of the waist-shaped slot hole are similar with those of the console hole with large divergence angle because of the effect of the waist-shaped slot hole’s structure. The middle constriction structure of the waist-shaped slot hole and the coupled vortices make jets from the waist-shaped slot holes produce higher cooling effectiveness in the midspan region between adjacent holes. And also due to the effect of the middle constriction structure, the heat transfer coefficient of the waist-shaped slot hole is very high in the upstream midspan region. However, the heat transfer coefficient in the downstream midspan region is lower than that in the region near the hole centerline because of the effect of the coupled vortices. The waist-shaped slot holes provide the surface with very good thermal protection, especially in the upstream region. Although the console holes with small exit-entry area ratio provide better thermal protection than the waist-shaped slot holes due to small turbulence intensity, the flow resistance characteristic of the waist-shaped slot hole is much better.

Numerical Study on the Effects of V-Shaped Rib Angle on Film Cooling Performance for Turbine Blade Trailing Edge

2018 ◽  
Author(s):  
Lin Ye ◽  
Cun-liang Liu ◽  
Hai-yong Liu ◽  
Qi-jiao He ◽  
Gang Xie
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Turbine Blade ◽  
Film Cooling ◽  
Trailing Edge ◽  
Cooling Effectiveness ◽  
Cooling Performance ◽  
Film Cooling Effectiveness ◽  
Blowing Ratio

The trailing edge of the high-pressure turbine blade presents significant challenges to cooling structure design. To achieve better cooling performance at turbine blade trailing edge, a novel ribbed cutback structure is proposed for trailing edge cooling, which has rib structures on the cutback surface for heat transfer enhancement. In this study, numerical simulations have been performed on the effects of V-shaped rib angle on the film cooling characteristics and flow physics. Three V-shaped rib angles of 30°, 45° and 60° are studied. The distributions of adiabatic cooling effectiveness and heat transfer coefficient are obtained under blowing ratios with the value of 0.5, 1.0 and 1.5 respectively. Due to the relatively small rib height, the effect of V-shaped ribs on the film cooling effectiveness is not notable. The disadvantage of V-shaped ribs mainly exhibits at the downstream area of cutback surface. With the increase of V-shaped rib angle, the film cooling effectiveness becomes lower, but the values are still above 0.9. The V-shaped ribs obviously enhance the heat transfer on trailing edge cutback surface. The area-averaged heat transfer coefficient of the V-rib case is higher than that of the smooth case by 26.3–41.2%. The 45° V-rib case has higher heat transfer intensity than the other two V-shaped rib cases under all the three blowing ratios. However, the heat transfer coefficient distribution of the 60° V-rib case is more uniform. The heat transfer intensity of the 30° V-rib case is higher in the downstream region than the other two cases, but lower in the upstream region in which the difference becomes smaller with the increase of blowing ratio. The 45° V-rib case and the 60° V-rib case both reach the maximum value of area-averaged heat transfer intensity under blowing ratio is 1.0. Under higher blowing ratio, the 30° V-rib case and the 45° V-rib case outperform 2.1% and 6.7% higher value relative to the 60° V-rib case respectively due to the smaller velocity gradient in the 60° V-rib case in the downstream.

The Effect of Freestream Turbulence on Film Cooling Heat Transfer Coefficient

2002 ◽  
Author(s):  
James E. Mayhew ◽  
James W. Baughn ◽  
Aaron R. Byerley
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Boundary Conditions ◽  
Transfer Coefficient ◽  
Film Cooling ◽  
Convective Heat Transfer Coefficient ◽  
High Heat ◽  
Freestream Turbulence ◽  
Thermochromic Liquid Crystal ◽  
High Heat Transfer

The film-cooling performance of a flat plate in the presence of low and high freestream turbulence is investigated using thermochromic liquid crystal thermography. Full-surface distributions of the convective heat transfer coefficient are determined for three blowing rates on a model with three straight holes spaced three diameters apart. An increase in heat transfer coefficient due to mass injection is clearly observed in the images and is quantitatively determined for both the low and high freestream turbulence cases. The increase in heat transfer coefficient is greater than in previously published research, possibly due to the use of different, more representative thermal boundary conditions upstream of the injection location. These boundary conditions, along with high resolution images, may account for the appearance of “fork tine” patterns of high heat transfer due to the presence of these vortices, not previously seen. Although the driving potential for heat transfer is less, it is observed that in some instances film cooling may cause an increase in overall heat transfer due to the increase in heat transfer coefficient.

Film Cooling Effectiveness and Mass/Heat Transfer Coefficient Downstream of One Row of Discrete Holes

1999 ◽  
Vol 121 (2) ◽  
pp. 225-232 ◽  
Author(s):  
R. J. Goldstein ◽  
P. Jin ◽  
R. L. Olson
Keyword(s):  
Heat Transfer ◽  
Mass Transfer ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Film Cooling ◽  
Density Ratio ◽  
Transfer Coefficients ◽  
Cooling Effectiveness ◽  
Cooling Performance ◽  
Film Cooling Effectiveness

A special naphthalene sublimation technique is used to study the film cooling performance downstream of one row of holes of 35 deg inclination angle with 3d hole spacing and relatively small hole length to diameter ratio (L/d = 6.3). Both film cooling effectiveness and mass/heat transfer coefficient are determined for blowing rates from 0.5 to 2.0 with density ratio of 1.0. The mass transfer coefficient is measured using pure air film injection, while the film cooling effectiveness is derived from comparison of mass transfer coefficients obtained following injection of naphthalene-vapor-saturated air with those from pure air injection. This technique enables one to obtain detailed local information on film cooling performance. The laterally averaged and local film cooling effectiveness agree with previous experiments. The difference between mass/heat transfer coefficients and previous heat transfer results indicates that conduction error may play an important role in the earlier heat transfer measurements.

Experimental Investigation of Film Cooling Performance for a New Shaped Hole at the Leading Edge

2014 ◽  
Author(s):  
Tarek Elnady ◽  
Ibrahim Hassan
Keyword(s):  
Heat Transfer ◽  
Experimental Investigation ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Film Cooling ◽  
Density Ratio ◽  
Leading Edge ◽  
Local Heat Transfer ◽  
Stagnation Line ◽  
Cooling Performance

An experimental investigation has been performed to study the film cooling performance of a smooth expansion exit at the leading edge of a gas turbine vane. A two-dimensional cascade has been employed to measure the cooling performance of the proposed expansion using the transient Thermochromatic Liquid Crystal technique. One row of cylindrical holes, located on the stagnation line, is investigated with two expansion levels, 2d and 4d, in addition to the standard hole. The air is injected at 90° and 60° inclination angle relative to the vane surface at four blowing ratios ranging from 1 to 2 at a 0.9 density ratio. The Mach number and the Reynolds number based on the cascade exit velocity and the axial chord are 0.23 and 1.4E5, respectively. The detailed local heat transfer coefficient over both the pressure side and the suction side are presented in addition to the lateral-averaged normalized heat transfer coefficient. The proposed expansion provides a lower heat transfer coefficient compared with the standard cylindrical hole over the investigated blowing ratios. Combining the heat transfer coefficient with the corresponding cooling effectiveness, previously presented, the smooth expansion shows a significant reduction in the heat load with more uniform distribution of the coolant over the leading edge region. The strong confrontation between the coolant jet and the mainstream, in case of 90° injection, yields a strong dispersion of the coolant with higher heat transfer coefficient and high thermal load over the vane surface.

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