The Comparison of Two Species Film Cooling Characteristics Between Trenched and Shaped Holes

2008 ◽  
Author(s):  
D. H. Zhang ◽  
Q. Y. Chen ◽  
L. Sun ◽  
M. Zeng ◽  
Q. W. Wang
Keyword(s):  
Film Cooling ◽  
Volume Fraction ◽  
Aerodynamic Performance ◽  
Diameter Ratio ◽  
Vapor Film ◽  
Cooling Effectiveness ◽  
Film Cooling Effectiveness ◽  
Shaped Hole ◽  
The Difference ◽  
Length To Diameter Ratio

The exit-shaped holes can result in lower coolant momentum injection with greater surface coverage. The exit-trenched holes can also lower the coolant momentum. Thus, the cooling and aerodynamic performance of laterally diffused shaped holes and laterally trenched holes were numerically compared with same depth and same hole length and the reasons for the difference were also analyzed from the viewpoint of flow mechanism. The both end-shaped holes and both end-trenched holes were also compared to the exit-shaped holes and exit-trenched holes respectively. Owing to the better heat transfer performance of steam than that of air, the cooling characteristics of super heated vapor film and pure air film were numerically investigated using the multi phase model of FLUENT to study the effect of different vapor volume fraction on film cooling characteristics. It appears that the shaped holes is superior to the trenched holes in cooling and aerodynamic performance for the cases in the present study; for shaped holes, the difference between the exit-shaped hole and both end-shaped hole is negligible; But for trenched holes, the cooling effectiveness of both end-trenched hole and the exit-trenched holes is heavily dependent on the hole length to diameter ratio; for shorter hole length to diameter ratio, the cooling effectiveness of both end-trenched hole is superior to that of exit-trenched hole. For all the cases studied, the mixture injectant is better than pure air coolant, and the mixture exhibits greater cooling advantage in the far downstream region of the holes than in the near hole region. The super heated vapor film can improve the film cooling effectiveness; the vapor volume fraction increased by 20%, and the area average cooling effectiveness can increase by 5%.

A Novel Method for Designing Fan-Shaped Holes With Short Length-to-Diameter Ratio in Producing High Film Cooling Performance for Thin-Wall Turbine Airfoil

2018 ◽  
Vol 140 (9) ◽  
Author(s):  
Weihong Li ◽  
Xueying Li ◽  
Jing Ren ◽  
Hongde Jiang
Keyword(s):  
Film Cooling ◽  
Diameter Ratio ◽  
Short Length ◽  
Transfer Coefficients ◽  
Cooling Effectiveness ◽  
Cooling Performance ◽  
Film Cooling Effectiveness ◽  
Heat Transfer Coefficients ◽  
Shaped Hole ◽  
Length To Diameter Ratio

An experimental investigation of the geometrical parameter effects on the film cooling performance of a fan-shaped hole was conducted on a low speed flat-plate facility. The pressure sensitive paint (PSP) technique and steady liquid crystal (SLC) technique were employed to determine the adiabatic film cooling effectiveness and heat transfer coefficients, respectively, for a blowing ratio ranging from 0.3 to 3 and a density ratio of DR = 1.5. Several geometrical parameters were investigated, including lateral expansion angle, length-to-diameter ratio, and hole entrance shape. Local, laterally averaged, and area-averaged adiabatic film cooling effectiveness, heat transfer coefficients, and net heat flux reduction (NHFR) were shown to provide a comprehensive understanding on the geometrical parameter effects on the thermal performance. A novel method was proposed for designing a fan-shaped hole with short length-to-diameter ratio to design to achieve high film cooling performance. The original and optimized fan-shaped holes were compared in terms of adiabatic film cooling effectiveness, heat transfer coefficients, and NHFR. Results showed that the optimized fan-shaped hole with short length-to-diameter ratio, large lateral diffusion angle, and slot hole entrance shape obtained highest overall thermal performance. It demonstrated the feasibility of adopting the proposed design method to design fan-shaped holes applied in thin wall gas turbine blades.

Numerical Investigation of Scoop Effect on Film Cooling for Cylindrical Inclined Hole

2017 ◽  
Author(s):  
Yongbin Ji ◽  
Prashant Singh ◽  
Srinath V. Ekkad ◽  
Shusheng Zhang
Keyword(s):  
Film Cooling ◽  
Three Dimensional ◽  
Diameter Ratio ◽  
Navier Stokes ◽  
Cooling Effectiveness ◽  
Film Cooling Effectiveness ◽  
Blowing Ratio ◽  
Sst Turbulence Model ◽  
Cooling Behavior ◽  
Length To Diameter Ratio

Film cooling behavior of a single cylindrical hole inclined at an angle of 35° with respect to a flat surface is numerically predicted in this study. Adiabatic film cooling effectiveness has been presented to evaluate the influence of the scoop placed on the coolant entry side. The effect of blowing ratio (0.65, 1, 1.5 and 2) and the length-to-diameter ratio (1.7 and 4.4) are examined. Three-dimensional Reynolds-averaged Navier-Stokes analysis with SST turbulence model is used for the computations. It has been found that both centerline and laterally averaged adiabatic film cooling effectiveness are enhanced by the scoop and the enhancement increases with the blowing ratio in the investigated range of variables. The scoop was more effective for the higher length-to-diameter ratio cases (L/D = 4.4) because of better velocity distribution at the film hole exit, which makes coolant reattach at a more upstream location after blowing off from the wall.

Large Eddy Simulation of Axial and Compound Angle Holes With Varying Hole Length-to-Diameter Ratio

2017 ◽  
Author(s):  
Weihong Li ◽  
Wei Shi ◽  
Xueying Li ◽  
Jing Ren ◽  
Hongde Jiang
Keyword(s):  
Large Eddy Simulation ◽  
Film Cooling ◽  
Vortex Structures ◽  
Diameter Ratio ◽  
Cooling Effectiveness ◽  
Film Cooling Effectiveness ◽  
Eddy Simulation ◽  
Large Eddy ◽  
Compound Angle ◽  
Length To Diameter Ratio

The effect of hole length to diameter ratio on flat plate film cooling effectiveness and flow structures of axial and compound angle hole is investigated by large eddy simulation (LES). Film cooling simulations are performed for three blowing ratios (M) ranging from 0.4 to 1.2, three hole length-to-diameter ratios (L/D) from 0.5 to 5 and two compound angle (β: 0°, 45°). The prediction accuracy is validated by the reported hydrodynamic data and present film effectiveness data measured by pressure sensitive paint (PSP). Results indicate that discrete hole with L = 0.5 show highest film cooling effectiveness regardless of compound angle. Round hole generally shows an increasing trend as L increases from 2 to 5, while compound angle hole shows a complex trend concerning with blowing ratios and length to diameter ratios. This is associated with the fact that length-to-diameter ratio influences the in-tube flow behavior, formation of Kelvin-Helmholtz (K-H) structures, and development of single asymmetric main vortex (SAMV). Scalar field transportation features are investigated to clarify how different vortex structures affect the temperature distribution and the film cooling effectiveness. It is also demonstrated that the counter rotating vortex pair (CRVP) which is observed in the time-averaged flow field of axial hole is originated in different vortex structures with varying blowing ratios and length to diameter ratios.

Influence of the Hole Length-to-Diameter Ratio on Film Cooling With Cylindrical Holes

1998 ◽  
Author(s):  
Ewald Lutum ◽  
Bruce V. Johnson
Keyword(s):  
Film Cooling ◽  
External Flow ◽  
Diameter Ratio ◽  
Cylindrical Hole ◽  
Coolant Flow ◽  
Hole Injection ◽  
Cooling Effectiveness ◽  
Film Cooling Effectiveness ◽  
Cylindrical Holes ◽  
Length To Diameter Ratio

Film cooling experiments were conducted to investigate the effects of coolant hole length-to-diameter ratio on the film cooling effectiveness. The results from these experiments offer an explanation for the differences between the film cooling results for cylindrical hole injection configurations previously reported by Goldstein et al. (1974), Pedersen et al. (1977) and Sinha et al. (1991). The previously reported injection configurations differed primarily in coolant hole length-to-diameter ratio. The present experiments were conducted with a row of cylindrical holes oriented at 35 degrees to a constant-velocity external flow, systematically varying the hole length-to-diameter ratios (L/D = 1.75, 3.5, 5, 7 and 18), and blowing rates (0.52≤M≤1.56). Results from these experiments show in a region 5≤X/D≤50 downstream of coolant injection that the coolant flow guiding capability in the cylindrical hole was apparently established after 5 hole diameters and no significant changes in the film cooling effectiveness distribution could be observed for the greater L/D. However, the film cooling effectiveness characteristics generally decreased with decreasing hole L/D ratio in the range of 1.75≤L/D≤5.0. This decrease in film cooling performance was attributed to (1) the undeveloped character of the flow in the coolant channels and (2) the greater effective injection angle of the coolant flow with respect to the external flow direction and surface. The lowest values of film cooling effectiveness were measured for the smallest hole length-to-diameter ratio, L/D = 1.75.

Effect of Breakout Angle on Tripod Injection Hole Geometries on Flat Plate Film Cooling

2012 ◽  
Author(s):  
Christopher LeBlanc ◽  
Sridharan Ramesh ◽  
Srinath Ekkad ◽  
Mary Anne Alvin
Keyword(s):  
Flat Plate ◽  
Film Cooling ◽  
Density Ratio ◽  
Diameter Ratio ◽  
Cylindrical Hole ◽  
Cooling Effectiveness ◽  
Film Cooling Effectiveness ◽  
Shaped Hole ◽  
Jet Interactions ◽  
Density Ratios

In this study, effect of breakout angle of side holes from the main hole in a tripod hole design on film cooling performance is evaluated on a flat plate surface with steady-state IR (infrared thermography) technique. The designs are compared a cylindrical hole design inclined at 30° from the surface with pitch-to-diameter ratio of 3.0 and a shaped hole design, which is identical to the cylindrical hole design with the addition of adding a 10° flare and laydown to the exit on the mainstream surface. The two tripod hole designs are one where the two side holes, also of the same diameter, branch from the root at a 15° angle while maintaining the same 30° inclination as the cylindrical and shaped designs witha pitch-to-diameter ratio between the main holes for this design is 6.0. The other tripod hole design is a modified tripod hole design that increases the branch angle to 30°, which has the added effect of increasing the pitch-to-diameter ratio between the main holes to 7.5. Two secondary fluids — air and carbon-dioxide — were used to study the effects of coolant-to-mainstream density ratio (DR = 0.95 and 1.45) on film cooling effectiveness. Several blowing ratios in the range 0.5–4.0 were investigated independently at the two density ratios. Results show that the tripod hole design provides similar film cooling effectiveness as the shaped hole case with overall reduced coolant usage. Increasing the breakout angle from 15° to 30° reduces overall cooling effectiveness but increases jet-to-jet interactions.

Influence of the Hole Length-to-Diameter Ratio on Film Cooling With Cylindrical Holes

1999 ◽  
Vol 121 (2) ◽  
pp. 209-216 ◽  
Author(s):  
E. Lutum ◽  
B. V. Johnson
Keyword(s):  
Film Cooling ◽  
External Flow ◽  
Diameter Ratio ◽  
Cylindrical Hole ◽  
Coolant Flow ◽  
Hole Injection ◽  
Cooling Effectiveness ◽  
Film Cooling Effectiveness ◽  
Cylindrical Holes ◽  
Length To Diameter Ratio

Film cooling experiments were conducted to investigate the effects of coolant hole length-to-diameter ratio on the film cooling effectiveness. The results from these experiments offer an explanation for the differences between the film cooling results for cylindrical hole injection configurations previously reported by Goldstein et al. (1974), Pedersen et al. (1977), and Sinha et al. (1991). The previously reported injection configurations differed primarily in coolant hole length-to-diameter ratio. The present experiments were conducted with a row of cylindrical holes oriented at 35 deg to a constant-velocity external flow, systematically varying the hole length-to-diameter ratios (L/D = 1.75, 3.5, 5, 7, and 18), and blowing rates (0.52 ≤ M ≤ 1.56). Results from these experiments show in a region 5 ≤ X/D ≤ 50 downstream of coolant injection that the coolant flow guiding capability in the cylindrical hole was apparently established after five hole diameters and no significant changes in the film cooling effectiveness distribution could be observed for the greater L/D. However, the film cooling effectiveness characteristics generally decreased with decreasing hole L/D ratio in the range of 1.75 ≤ L/D ≤ 5.0. This decrease in film cooling performance was attributed to (1) the undeveloped character of the flow in the coolant channels and (2) the greater effective injection angle of the coolant flow with respect to the external flow direction and surface. The lowest values of film cooling effectiveness were measured for the smallest hole length-to-diameter ratio, L/D = 1.75.

Enhancement of Full Coverage Film Cooling Effectiveness with Mixed Injection Holes

2018 ◽  
Vol 0 (0) ◽  
Author(s):  
Mukesh Prakash Mishra ◽  
A K Sahani ◽  
Sunil Chandel ◽  
R K Mishra
Keyword(s):  
Film Cooling ◽  
Numerical Study ◽  
Velocity Ratio ◽  
Perforated Plate ◽  
Combustion Chambers ◽  
Cooling Effectiveness ◽  
Film Cooling Effectiveness ◽  
Full Coverage ◽  
Upstream Direction ◽  
The Difference

Abstract In the present work numerical study of full coverage film cooling on an adiabatic flat plate is carried out. Cooling performance of three configurations of cylindrical holes is studied with downstream injection, upstream injection and mixed injection. In mixed injection configuration one column of holes inject in downstream direction and the holes in the adjacent column inject in the upstream direction. Numerical simulations are carried out at different velocity ratios and circumferentially averaged value of adiabatic film cooling effectiveness is estimated. Simulation results indicate that the mixed injection configuration has better and more uniform cooling, throughout the perforated plate, than with downstream injection. The difference is greater with increase in the velocity ratio. Configuration with upstream injection gives better cooling than mixed injection at front few rows of cooling holes but it shows poorer performance with downstream injection in the downstream rows of cooling holes. The obtained results from this study can be an invaluable input for highly loaded combustion chambers.

Film Cooling Mechanism of Combined Hole and Saw-tooth Slot

2019 ◽  
Vol 36 (4) ◽  
pp. 425-433
Author(s):  
Wei Zhang ◽  
Shuai Zhou ◽  
Zhuang Wu ◽  
Guangchao Li ◽  
Zhihai Kou
Keyword(s):  
Film Cooling ◽  
Numerical Data ◽  
Diameter Ratio ◽  
Cooling Effectiveness ◽  
Cooling Performance ◽  
Film Cooling Effectiveness ◽  
Inclination Angles ◽  
Cylindrical Holes ◽  
Cooling Mechanism ◽  
Experimental Values

Abstract Film cooling performance of one row of cylindrical holes integrated with saw-tooth slots was numerically studied at blowing ratios of 0.5, 1.0 1.5 and 2.0 respectively. The saw-tooth slot concept combines the advantages both of easy machining for the slot and of the high film cooling effectiveness caused by the anti-vortex induced by the shaped hole. The film holes have an inclination angles of 30°, length to diameter ratio of 4 and pitch to diameter ratio of 3. The corner angles of the saw-tooth are 60°, 90°, 120°, 150° and 180° respectively. The 180° corner angle corresponds to a standard transverse slot. The emphasis of this other is on the influence of the corner angles of the saw-tooth on film cooling effectiveness. The flow field and thermal field were obtained to explain the mechanism of film cooling performance improvement by the saw-tooth slot. The results show that the numerical data agrees with the experimental values for the cylindrical holes. Relatively small corner angles generate uniform local film cooling effectiveness and high spanwise averaged film cooling effectiveness due to the coolant ejected from the hole smoothly flowing into the slot. The effect of corner angles strongly depends on blowing ratios. The increase of x/D decreases the differences of film cooling effectiveness between various corner angles. At low blowing ratios, an anti-vortex can be found with the spanwise angle of 60° and 120°. At high blowing ratios, an anti-vortex can be found with the spanwise angle of 60°.

Experimental Investigation and Optimal Design on the Film Cooling Performance of Fan-Shaped Hole With Vortex Generator Fed by Crossflow

2021 ◽  
Author(s):  
Jie Wang ◽  
Chao Zhang ◽  
Xuebin Liu ◽  
Liming Song ◽  
Jun Li ◽  
...  
Keyword(s):  
Reynolds Number ◽  
Film Cooling ◽  
Vortex Generator ◽  
Optimized Design ◽  
Combined Model ◽  
Cooling Effectiveness ◽  
Cooling Performance ◽  
Film Cooling Effectiveness ◽  
Blowing Ratio ◽  
Shaped Hole

Abstract Aiming at investigating the effects of crossflow and vortex generator on film cooling characteristics of fan-shaped hole, the film cooling performance was measured experimentally by infrared camera. The blowing ratio is fixed at 0.5 and 1.5. The Reynolds number of the mainstream based on the hole diameter remains at 7000 and the inlet Reynolds number of crossflow is 40000. The experimental results show that the film cooling performance becomes better when the blowing ratio increases from 0.5 to 1.5 for each model, and the film cooling performance becomes worse under the influence of crossflow. When the blowing ratio is 1.5, the area-averaged film cooling effectiveness of the fan-shaped hole model with vortex generator decreases by 16.6% because of the influence of crossflow. The combined model always performs better compared with the model without vortex generator under all working conditions. When the blowing ratio becomes 1.5, under the influence of crossflow, the area-averaged film cooling effectiveness of the combined model could increase by 14.8%, compared with the model without vortex generator. To further improve the film cooling performance, the global optimization algorithm based on the Kriging method and the CFD technology are coupled to optimize the combined model under crossflow condition at the high blowing ratio, and the optimized design is verified by experiments. The experimental results show that the area-averaged film cooling effectiveness of the optimized design increases by 17.8% compared with the reference model.

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