Effect of length-to-diameter ratio on film cooling and heat transfer performances of simple and compound cylindrical-holes in transverse trenches with various depths

2021 ◽  
pp. 122328
Author(s):  
Xin Huang ◽  
Jian Pu ◽  
Tiao Zhang ◽  
Jian-Hua Wang ◽  
Wei-Long Wu ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Film Cooling ◽  
Diameter Ratio ◽  
Cylindrical Holes ◽  
Length To Diameter Ratio

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.

Film Cooling Characteristic of Double-Fan-Shaped Film Cooling Holes

2009 ◽  
Author(s):  
Jiang-Tao Bai ◽  
Hui-ren Zhu ◽  
Cun-liang Liu
Keyword(s):  
Heat Transfer ◽  
Numerical Simulation ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Film Cooling ◽  
Diameter Ratio ◽  
Cooling Effectiveness ◽  
Film Cooling Effectiveness ◽  
Cylindrical Holes ◽  
Film Cooling Holes

The film cooling performance downstream of a single row of double-fan-shaped film cooling holes in a flat plate have been investigated by experimental measurements and numerical simulation. The entrance and exit of double-fan-shaped holes are comprised of a lateral expansion of 15° from the original simple cylindrical shape with stream-wise inclination of 45°. The width of the exit face to cylinder diameter ratio is 1.5; the length-to-diameter ratio is 4.24 and the pitch-to-diameter ratio is 3. The experimental method used to obtain the adiabatic film cooling effectiveness values and the heat transfer coefficient is a transient narrow band liquid crystal technique. Both film cooling effectiveness and heat transfer coefficient are measured at three momentum ratios (I = 0.5, 1, 2) at constant Reynolds number (Re = 10000) and free stream turbulence (Tu = 2%). The film cooling effectiveness, heat transfer coefficient and Net Heat Flux Reduction (NHFR) are presented for detailed distribution and span-wise averaged values. Discharge coefficients are also measured in the experiment. A commercial package is used to numerically simulate the flow and heat transfer of double-fan-shaped holes; simple cylindrical holes are also simulated for comparison. Numerical simulation use RNG turbulence model with a standard wall function for near wall region. Experimental and Numerical simulation results show that: 1) the double-fan-shaped holes present higher discharge coefficient than simple cylindrical holes at respective momentum ratio; 2) the numerical simulation film cooling effectiveness results of double-fan-shaped holes accord well with the experimental results; 3) at measured three momentum ratios, the double-fan-shaped holes demonstrate better film cooling performance (higher NHFR) than simple cylindrical holes, better film cooling expansion on span-wise; 4) the best momentum ratio of double-fan-shaped holes is 0.5.

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.

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°.

Heat Transfer Measurements Downstream of Trenched Film Cooling Holes Using a Novel Optical Two-Layer Measurement Technique

2015 ◽  
Vol 138 (3) ◽  
Author(s):  
Peter Schreivogel ◽  
Michael Pfitzner
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Film Cooling ◽  
Slight Reduction ◽  
Superposition Method ◽  
Cooling Effectiveness ◽  
Cylindrical Holes ◽  
The Heat Transfer Coefficient

A new approach for steady-state heat transfer measurements is proposed. Temperature distributions are measured at the surface and a defined depth inside the wall to provide boundary conditions for a three-dimensional heat flux calculation. The practical application of the technique is demonstrated by employing a superposition method to measure heat transfer and film cooling effectiveness downstream of two different 0.75D deep narrow trench geometries and cylindrical holes. Compared to the cylindrical holes, both trench geometries lead to an augmentation of the heat transfer coefficient supposedly caused by the highly turbulent attached cooling film emanating from the trenches. Areas of high heat transfer are visible, where recirculation bubbles or large amounts of coolant are expected. Increasing the density ratio from 1.33 to 1.60 led to a slight reduction of the heat transfer coefficient and an increased cooling effectiveness. Both trenches provide a net heat flux reduction (NHFR) superior to that of cylindrical holes, especially at the highest momentum flux ratios.

Velocity and Turbulence Intensity Profiles Downstream of a Long Reach Endwall Double Row of Film Cooling Holes in a Gas Turbine Combustor Representative Environment

2015 ◽  
Author(s):  
Irene Cresci ◽  
Peter T. Ireland ◽  
Marko Bacic ◽  
Ian Tibbott ◽  
Anton Rawlinson
Keyword(s):  
Flow Field ◽  
Turbulence Intensity ◽  
Film Cooling ◽  
Momentum Flux ◽  
Diameter Ratio ◽  
Double Row ◽  
Length Scales ◽  
Cylindrical Holes ◽  
Endwall Film Cooling ◽  
Film Cooling Holes

The continuous demand from the airlines for reduced jet engine fuel consumption results in increasingly challenging high pressure turbine nozzle guide vane (NGV) working conditions. The capability to reproduce realistic boundary conditions in a rig at the combustor-turbine interaction plane is a key feature when testing NGVs in an engine-representative environment. A large scale linear cascade rig to investigate NGV leading edge cooling systems has been designed with particular attention being paid to creating engine representative conditions at the inlet to the NGVs. The combustor simulator replicates the main features of a rich-burn design including large dilution jets and extensive endwall film cooling. A three-dimensional computational domain including the entire combustor simulator has been created and RANS CFD simulations have been run in order to match Reynolds number and mainstream-to-coolant momentum flux ratio; velocity and turbulence measurements have been acquired at the NGV inlet plane at ambient temperature. In this engine-representative environment the authors focused their attention on the flow field downstream of different endwall film cooling holes configurations: three arrangements of a double row of staggered cylindrical holes (lateral pitch-to-diameter ratio of 2–3–6) and one with intersecting holes (intersecting angle of 90°) are experimentally and numerically analyzed. Velocity, turbulence intensity and integral length scales are predicted and measured for a density ratio of 1 and coolant-to-mainstream momentum flux of 6. A hot wire sensor was mounted on a two-axis traverse mechanism able to move the probe in the spanwise and lateral directions. Three slots allowed to reposition the traverse and take measurements at three downstream locations (stream-wise distance-to-diameter ratio of 4.2–9.2–14.2). The research confirmed the strong influence of the endwall coolant on the flow field at the NGV inlet plane and the hole spacing results a key parameter in managing the film development. Closer-spaced hole configurations can assure an effective film coverage. The integral length scales are strongly connected to the hole diameter and spacing. Intersecting holes can potentially reduce the amount of required coolant at a fixed pressure ratio, but they offer worst film performance than cylindrical holes. RANS simulations proved to be able to get the main trends shown by the measurements.

Film Cooling From a Row of Holes With Both Ends Embedded in Transverse Slots

2008 ◽  
Author(s):  
D. H. Zhang ◽  
L. Sun ◽  
Q. Y. Chen ◽  
M. Lin ◽  
M. Zeng ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Film Cooling ◽  
Aerodynamic Performance ◽  
Transfer Coefficients ◽  
Cooling Effectiveness ◽  
Cooling Performance ◽  
Film Cooling Effectiveness ◽  
Heat Transfer Coefficients ◽  
Discharge Coefficients ◽  
Cylindrical Holes

Embedding a row of typical cylindrical holes in a transverse slot can improve the cooling performance. Rectangular slots can increase the cooling effectiveness but is at the cost of decreasing of discharge coefficients. An experiment is conducted to examine the effects of an overlying transverse inclined trench on the film cooling performance of axial holes. Four different trench configurations are tested including the baseline inclined cylindrical holes. The influence of the geometry of the upstream lip of the exit trench and the geometry of the inlet trench on cooling performance is examined. Detailed film cooling effectiveness and heat transfer coefficients are obtained separately using the steady state IR thermography technique. The discharge coefficients are also acquired to evaluate the aerodynamic performance of different hole configurations. The results show that the film cooling holes with both ends embedded in slots can provide higher film cooling effectiveness and lower heat transfer coefficients; it also can provide higher discharge coefficients whilst retaining the mechanical strength of a row of discrete holes. The cooling performance and the aerodynamic performance of the holes with both ends embedded in inclined slots are superior to the holes with only exit trenched. To a certain extent, the configuration of the upstream lip of the exit trench affects the cooling performance of the downstream of the trench. The filleting for the film hole inlet avail the improvement of the cooling effect, but not for the film hole outlet. Comparing film cooling with embedded holes to unembedded holes, the overall heat flux ratio shows that the film holes with both ends embedded in slots and filleting for the film hole inlet can produce the highest heat flux reduction.

Effect of Trench Width and Depth on Film Cooling From Cylindrical Holes Embedded in Trenches

2007 ◽  
Author(s):  
Yiping Lu ◽  
Alok Dhungel ◽  
Srinath V. Ekkad ◽  
Ronald S. Bunker
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Film Cooling ◽  
Cfd Simulation ◽  
Lateral Spreading ◽  
Stream Velocity ◽  
Clear Understanding ◽  
Cylindrical Holes ◽  
Trench Width

The present study is an experimental investigation of film cooling from cylindrical holes embedded in transverse trenches. Different trench depths are considered with two trench widths. Trench holes can occur when blades are coated with thermal barrier coating (TBC) layers. The film hole performance and behavior will be different for the trench holes compared to standard cylindrical holes that are flush with the surface. The trench width and depth depends on the mask region and the thickness of the TBC layer. Detailed heat transfer coefficient and film effectiveness measurements are obtained simultaneously using a single test transient IR thermography technique. The study is performed at a single mainstream Reynolds number based on free-stream velocity and film hole diameter of 11000 at four different coolant-to-mainstream blowing ratios of 0.5, 1.0, 1.5 and 2.0. The results show that film effectiveness is greatly enhanced by the trenching due to improved two dimensional nature of the film and lateral spreading. The detailed heat transfer coefficient and film effectiveness contours provide a clear understanding of the jet-mainstream interactions for different hole orientations. CFD simulation using Fluent was also performed to determine the jet mainstream interactions to better understand the surface heat transfer coefficient and film effectiveness distributions.

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