Analysis of Film Cooling With High-Aspect-Ratio Holes: Heat Transfer Mechanisms

2017 ◽  
Author(s):  
Hao-Ming Li ◽  
Wahid Ghaly ◽  
Ibrahim Hassan
Keyword(s):  
Aspect Ratio ◽  
High Aspect Ratio ◽  
Film Cooling ◽  
Density Ratio ◽  
Vortex Pair ◽  
Cooling Effectiveness ◽  
Film Cooling Effectiveness ◽  
Coverage Ratio ◽  
Counter Rotating Vortex Pair ◽  
Transfer Mechanisms

A new advanced film cooling scheme, named high-aspect-ratio holes has been proposed. Four configurations were designed, and numerically simulated under density ratio of 2 and different blowing ratios. All configurations demonstrate extremely high film cooling effectiveness values, some are as high as the so-called perfect performance, while their mechanical strength are similar to the conventional schemes. The new scheme exhibits two traits distinctive from the conventional geometries: Its film cooling effectiveness is much higher than the coverage ratio (t/P), and the high film cooling effectiveness is obtained under strong counter-rotating vortex pair (CRVP). It has been found that, in the new scheme, along with the aspect ratio value increase, the CRVP move away from the coolant-mainstream interface, and the coolant laterally expands in the vicinity of the exit. Consequently, a continuous coolant film would occur near the trailing edge position if aspect ratio is high enough. The approach of high-aspect-ratio holes could be used to design the highest film cooling performance geometries.

Film Cooling of Cylindrical Hole With a Downstream Short Crescent-Shaped Block

2013 ◽  
Vol 135 (3) ◽  
Author(s):  
Baitao An ◽  
Jianjun Liu ◽  
Chao Zhang ◽  
Sijing Zhou
Keyword(s):  
Film Cooling ◽  
Density Ratio ◽  
Vortex Pair ◽  
Cylindrical Hole ◽  
Test Case ◽  
Main Body ◽  
Lateral Direction ◽  
Cooling Effectiveness ◽  
Film Cooling Effectiveness ◽  
Cooling Hole

This paper presents a method to improve the film-cooling effectiveness of cylindrical holes. A short crescent-shaped block is placed at the downstream of a cylindrical cooling hole. The block shape is defined by a number of geometric parameters including block height, length and width, etc. The single row hole on a flat plate with inclination angle of 30 deg, pitch ratio of 3, and length-diameter ratio of 6.25 was chosen as the baseline test case. Film-cooling effectiveness for the cylindrical hole with or without the downstream short crescent-shaped block was measured by using the pressure sensitive paint (PSP) technique. The density ratio of coolant (argon) to mainstream air is 1.38. The blowing ratios vary from 0.5 to 1.25. The results showed that the lateral averaged cooling effectiveness is increased remarkably when the downstream block is present. The downstream short block allows the main body of the coolant jet to pass over the block top and to form a new down-wash vortex pair, which increases the coolant spread in the lateral direction. The effects of each geometrical parameter of the block on the film-cooling effectiveness were studied in detail.

Interaction of Flow and Film-Cooling Effectiveness Between Double-Jet Film-Cooling Holes With Various Spanwise Distances

2018 ◽  
Vol 140 (12) ◽  
Author(s):  
Jiaxu Yao ◽  
Jin Xu ◽  
Ke Zhang ◽  
Jiang Lei ◽  
Lesley M. Wright
Keyword(s):  
Flat Plate ◽  
Film Cooling ◽  
Density Ratio ◽  
Vortex Pair ◽  
Cooling Effectiveness ◽  
Film Cooling Effectiveness ◽  
Blowing Ratio ◽  
Film Cooling Holes ◽  
Two Jets ◽  
Compound Angle

The interaction of flow and film-cooling effectiveness between jets of double-jet film-cooling (DJFC) holes on a flat plate is studied experimentally. The time-averaged flow field in several axial positions (X/d = −2.0, 1.0, and 5.0) is obtained through a seven-hole probe. The downstream film-cooling effectiveness on the flat plate is measured by pressure sensitive paint (PSP). The inclination angle (θ) of all the holes is 35 deg, and the compound angle (β) is ±45 deg. Effects of the spanwise distance (p = 0, 0.5d, 1.0d, 1.5d, and 2.0d) between the two interacting jets of DJFC holes are studied, while the streamwise distance (s) is kept as 3d. The blowing ratio (M) varies as 0.5, 1.0, 1.5, and 2.0. The density ratio (DR) is maintained at 1.0. Results show that the interaction between the two jets of DJFC holes has different effects at different spanwise distances. For a small spanwise distance (p/d = 0), the interaction between the jets presents a pressing effect. The downstream jet is pressed down and kept attached to the surface by the upstream one. The effectiveness is not sensitive to blowing ratios. For mid-spanwise distances (p/d = 0.5 and 1.0), the antikidney vortex pair dominates the interaction and pushes both of the jets down, thus leading to better coolant coverage and higher effectiveness. As the spanwise distance becomes larger (p/d ≥ 1.5), the pressing effect almost disappears, and the antikidney vortex pair effect is weaker. The jets separate from each other and the coolant coverage decreases. At a higher blowing ratio, the interaction between the jets of DJFC holes happens later.

Geometrical Parameter Effects on Film-Cooling Effectiveness of Rectangular Diffusion Holes

2017 ◽  
Vol 139 (8) ◽  
Author(s):  
Bai-Tao An ◽  
Jian-Jun Liu ◽  
Si-Jing Zhou
Keyword(s):  
Aspect Ratio ◽  
Film Cooling ◽  
Density Ratio ◽  
Lateral Diffusion ◽  
Cooling Effectiveness ◽  
Film Cooling Effectiveness ◽  
Blowing Ratio ◽  
Film Distribution ◽  
Aspect Ratios ◽  
Shaped Hole

This paper presents an experimental investigation of the rectangular diffusion hole. The effects of rectangular aspect ratio and lateral diffusion angle on film-cooling effectiveness were studied at a low-speed flat-plate experimental facility. The pressure-sensitive paint (PSP) measurement technique was employed to determine the adiabatic effectiveness. The experiments were performed at a density ratio of DR = 1.38 and a mainstream turbulence intensity of Tu = 3.5%. The blowing ratio was varied from M = 0.5 to M = 2.5. Three aspect ratios and three lateral diffusion angles were chosen to match the semicircle and straight-line sidewall shape of the rectangular cross section. A comparative investigation was performed among a typical fan-shaped hole and ten rectangular diffusion holes. The experimental results exhibited diversified film distribution patterns of the rectangular diffusion hole, including single-, bi-, and tripeak patterns. The overall cooling effectiveness increased with the increase of rectangular aspect ratio. The improved magnitude was amplified as blowing ratio increased. The holes with semicircle sidewall were shown to be more suitable for high blowing ratio conditions. The maximum increase of cooling effectiveness was over 70% compared to the fan-shaped hole. The reduction of the lateral diffusion angle affected the film distribution pattern significantly, thereby influencing the cooling effectiveness. To obtain a fixed coverage ratio of film hole row, the rectangular diffusion hole with a larger cross-sectional aspect ratio and a slightly smaller lateral diffusion angle is a preferred scheme.

Interaction of Flow and Film-Cooling Effectiveness Between Double-Jet Film-Cooling Holes With Various Spanwise Distances

2017 ◽  
Author(s):  
Jiaxu Yao ◽  
Jin Xu ◽  
Ke Zhang ◽  
Jiang Lei ◽  
Lesley M. Wright
Keyword(s):  
Flat Plate ◽  
Film Cooling ◽  
Density Ratio ◽  
Vortex Pair ◽  
Cooling Effectiveness ◽  
Film Cooling Effectiveness ◽  
Blowing Ratio ◽  
Film Cooling Holes ◽  
Two Jets ◽  
Compound Angle

The interaction of flow and film-cooling effectiveness between jets of double-jet film-cooling (DJFC) holes on a flat plate is studied experimentally. The time-averaged secondary flow field in several axial positions (X/d = −2.0, 1.0, and 5.0) is obtained through a seven-hole probe. The downstream film-cooling effectiveness on the flat plate is achieved by Pressure Sensitive Paint (PSP). The inclination angle (θ) of all holes is 35°, and the compound angle (β) is ±45°. Effects of spanwise distance (p = 0, 0.5d, 1.0d, 1.5d, 2.0d) between the two interacting jets of DJFC holes are studied while streamwise distance (s) is kept as 3d. The blowing ratio (M) varies as 0.5, 1.0, 1.5, and 2.0. The density ratio (DR) is maintained at 1.0. Results show that the interaction between two jets of DJFC holes has different effects for different spanwise distance. For a small spanwise distance (p/d = 0), the interaction between jets presents a pressing effect. The downstream jet is pressed down and kept attached to the surface by the upstream one. The effectiveness is not sensitive to blowing ratios. For mid spanwise distances (p/d = 0.5 and 1.0), the anti-kidney vortex pair dominates the interaction, and pushes both of the jets down, thus leads to better coolant coverage and higher effectiveness. As spanwise distance becomes larger (p/d≥1.5), the pressing effect almost disappears, and the anti-kidney vortex pair effect is weaker. The jets separate from each other and the coolant coverage decreases. At higher blowing ratio, the interaction between the two jets of DJFC holes moves more downstream.

Numerical Investigation of Film Cooling Enhancement Using Staggered Row Mixed Hole Arrangements

2017 ◽  
Vol 9 (2) ◽  
Author(s):  
Prakhar Jindal ◽  
Shubham Agarwal ◽  
R. P. Sharma ◽  
A. K. Roy
Keyword(s):  
Film Cooling ◽  
Vortex Pair ◽  
Temperature Fields ◽  
Flow Temperature ◽  
Cooling Effectiveness ◽  
Film Cooling Effectiveness ◽  
Jet Interaction ◽  
Blowing Ratio ◽  
Cooling Enhancement ◽  
Counter Rotating Vortex Pair

The paper presents a novel study on film cooling effectiveness of a 3D flat plate with a multihole arrangement of mixed hole shapes. The film cooling arrangement consists of two rows of coolant holes, organized in a staggered pattern with an L/D (length to diameter ratio) of 10. The two rows consist of varied combinations of triangular and semi-elliptic shaped holes for the enhancement of film-cooling effectiveness. The results were obtained for a coolant to mainstream temperature ratio of 0.5 and a blowing ratio of 1.0. The computed flow temperature fields are presented in addition to the local two-dimensional streamwise and spanwise distribution of film cooling effectiveness. Validation of the results obtained from the turbulence model has been done with the experimental data of centerline film cooling effectiveness downstream of the cooling holes available in the open literature. The results showed the rapid merging of coolant jets emerging from front row of multiholes with the secondary staggered row of mixed holes. Due to the mainstream–coolant jet interaction, the strength of the counter rotating vortex pair was mitigated in the downstream region for certain arrangement of mixed hole shapes. The optimal hole combination with maximum overall effectiveness has been deduced from this study. The best configuration (M.R. VI) not only favored for the developed film, but also enhanced the averaged film cooling effectiveness to a large extent.

Film Cooling Effectiveness Improvements Using a Non-Diffusing Oval Hole

2015 ◽  
Author(s):  
Emin Issakhanian ◽  
Christopher J. Elkins ◽  
John K. Eaton
Keyword(s):  
Film Cooling ◽  
Vortex Pair ◽  
Round Hole ◽  
Blade Surface ◽  
Cooling Effectiveness ◽  
Film Cooling Effectiveness ◽  
Cooling Hole ◽  
Counter Rotating Vortex Pair ◽  
Shaped Hole ◽  
Film Cooling Holes

The need for improvements in film cooling effectiveness over traditional cylindrical film cooling holes has led to varied shaped hole and sister hole designs of increasing complexity. This paper presents a simpler shaped-hole design which shows improved film cooling effectiveness over both cylindrical holes and diffusing fan-shaped holes without the geometric complexity of the latter. Magnetic resonance imaging measurement techniques are used to reveal the coupled 3D velocity and coolant mixing from film cooling holes which are of a constant oval cross-section as opposed to round. The oval shaped hole yielded an area-averaged adiabatic effectiveness twice that of the diffusing fan-shaped hole tested. Three component mean velocity measurements within the channel and cooling hole showed the flow features and vorticity fields which explain the improved performance of the oval shaped hole. As compared to the round hole, the oval hole leads to a more complex vorticity field which reduces the strength of the main counter-rotating vortex pair. The counter-rotating vortex pair acts to lift the coolant away from the turbine blade surface and thus strongly reduces the film cooling effectiveness. The weaker vortices allow coolant to stay closer to the blade surface and to remain relatively unmixed with the main flow over a longer distance. Thus, the oval-shaped film cooling hole provides a simpler solution for improving film cooling effectiveness beyond circular hole and diffusing hole designs.

Conjugate Heat Transfer and Film Cooling of a Multi-Stage Cooling Scheme

2008 ◽  
Author(s):  
M. Ghorab ◽  
S. I. Kim ◽  
I. Hassan
Keyword(s):  
Heat Transfer ◽  
Film Cooling ◽  
Gas Turbines ◽  
Conjugate Heat Transfer ◽  
Density Ratio ◽  
Design Parameters ◽  
Cooling Effectiveness ◽  
Film Cooling Effectiveness ◽  
Multi Stage ◽  
Internal Gap

Cooling techniques play a key role in improving efficiency and power output of modern gas turbines. The conjugate technique of film and impingement cooling schemes is considered in this study. The Multi-Stage Cooling Scheme (MSCS) involves coolant passing from inside to outside turbine blade through two stages. The first stage; the coolant passes through first hole to internal gap where the impinging jet cools the external layer of the blade. Finally, the coolant passes through the internal gap to the second hole which has specific designed geometry for external film cooling. The effect of design parameters, such as, offset distance between two-stage holes, gap height, and inclination angle of the first hole, on upstream conjugate heat transfer rate and downstream film cooling effectiveness performance are investigated computationally. An Inconel 617 alloy with variable properties is selected for the solid material. The conjugate heat transfer and film cooling characteristics of MSCS are analyzed across blowing ratios of Br = 1 and 2 for density ratio, 2. This study presents upstream wall temperature distributions due to conjugate heat transfer for different gap design parameters. The maximum film cooling effectiveness with upstream conjugate heat transfer is less than adiabatic film cooling effectiveness by 24–34%. However, the full coverage of cooling effectiveness in spanwise direction can be obtained using internal cooling with conjugate heat transfer, whereas adiabatic film cooling effectiveness has narrow distribution.

Assessment of a Double Hole Film Cooling Geometry Using S-PIV and PSP

2013 ◽  
Author(s):  
Lesley M. Wright ◽  
Stephen T. McClain ◽  
Charles P. Brown ◽  
Weston V. Harmon
Keyword(s):  
Film Cooling ◽  
Density Ratio ◽  
Three Dimensional ◽  
Field Measurements ◽  
Secondary Flows ◽  
Cylindrical Hole ◽  
Cooling Effectiveness ◽  
Film Cooling Effectiveness ◽  
Hole Geometry ◽  
Compound Angle

A novel, double hole film cooling configuration is investigated as an alternative to traditional cylindrical and fanshaped, laidback holes. This experimental investigation utilizes a Stereo-Particle Image Velocimetry (S-PIV) to quantitatively assess the ability of the proposed, double hole geometry to weaken or mitigate the counter-rotating vortices formed within the jet structure. The three-dimensional flow field measurements are combined with surface film cooling effectiveness measurements obtained using Pressure Sensitive Paint (PSP). The double hole geometry consists of two compound angle holes. The inclination of each hole is θ = 35°, and the compound angle of the holes is β = ± 45° (with the holes angled toward one another). The simple angle cylindrical and shaped holes both have an inclination angle of θ = 35°. The blowing ratio is varied from M = 0.5 to 1.5 for all three film cooling geometries while the density ratio is maintained at DR = 1.0. Time averaged velocity distributions are obtained for both the mainstream and coolant flows at five streamwise planes across the fluid domain (x/d = −4, 0, 1, 5, and 10). These transverse velocity distributions are combined with the detailed film cooling effectiveness distributions on the surface to evaluate the proposed double hole configuration (compared to the traditional hole designs). The fanshaped, laidback geometry effectively reduces the strength of the kidney-shaped vortices within the structure of the jet (over the entire range of blowing ratios considered). The three-dimensional velocity field measurements indicate the secondary flows formed from the double hole geometry strengthen in the plane perpendicular to the mainstream flow. At the exit of the double hole geometry, the streamwise momentum of the jets is reduced (compared to the single, cylindrical hole), and the geometry offers improved film cooling coverage. However, moving downstream in the steamwise direction, the two jets form a single jet, and the counter-rotating vortices are comparable to those formed within the jet from a single, cylindrical hole. These strong secondary flows lift the coolant off the surface, and the film cooling coverage offered by the double hole geometry is reduced.

Influence of Coolant Density on Turbine Platform Film-Cooling With Stator–Rotor Purge Flow and Compound-Angle Holes

2014 ◽  
Vol 6 (4) ◽  
Author(s):  
Kevin Liu ◽  
Shang-Feng Yang ◽  
Je-Chin Han
Keyword(s):  
Film Cooling ◽  
Density Ratio ◽  
Cooling Effectiveness ◽  
Film Cooling Effectiveness ◽  
Fundamental Parameters ◽  
Blowing Ratio ◽  
Purge Flow ◽  
Cylindrical Holes ◽  
Exit Mach Number ◽  
Compound Angle

A detailed parametric study of film-cooling effectiveness was carried out on a turbine blade platform. The platform was cooled by purge flow from a simulated stator–rotor seal combined with discrete hole film-cooling. The cylindrical holes and laidback fan-shaped holes were accessed in terms of film-cooling effectiveness. This paper focuses on the effect of coolant-to-mainstream density ratio on platform film-cooling (DR = 1 to 2). Other fundamental parameters were also examined in this study—a fixed purge flow of 0.5%, three discrete-hole film-cooling blowing ratios between 1.0 and 2.0, and two freestream turbulence intensities of 4.2% and 10.5%. Experiments were done in a five-blade linear cascade with inlet and exit Mach number of 0.27 and 0.44, respectively. Reynolds number of the mainstream flow was 750,000 and was based on the exit velocity and chord length of the blade. The measurement technique adopted was the conduction-free pressure sensitive paint (PSP) technique. Results indicated that with the same density ratio, shaped holes present higher film-cooling effectiveness and wider film coverage than the cylindrical holes, particularly at higher blowing ratios. The optimum blowing ratio of 1.5 exists for the cylindrical holes, whereas the effectiveness for the shaped holes increases with an increase of blowing ratio. Results also indicate that the platform film-cooling effectiveness increases with density ratio but decreases with turbulence intensity.

Numerical Investigation of Effects of Blockage, Inclination Angle, and Hole-Size on Film Cooling Effectiveness at Concave Surface

2021 ◽  
Vol 143 (2) ◽  
Author(s):  
Fu-qiang Wang ◽  
Jian Pu ◽  
Jian-hua Wang ◽  
Wei-dong Xia
Keyword(s):  
Film Cooling ◽  
Pressure Loss ◽  
Numerical Study ◽  
Density Ratio ◽  
Concave Surface ◽  
Blockage Ratio ◽  
Coverage Area ◽  
Cooling Effectiveness ◽  
Film Cooling Effectiveness ◽  
Injection Angle

Abstract Film-hole can be often blocked by thermal-barrier coatings (TBCs) spraying, resulting in the variations of aerodynamic and thermal performances of film cooling. In this study, a numerical study of the blockage effect on the film cooling effectiveness of inclined cylindrical-holes was carried out on a concave surface to simulate the airfoil pressure side. Three typical blowing ratios (BRs) of 0.5, 1.0, and 1.5 were chosen at an engine-similar density ratio (DR) of 2.0. Two common inclination angles of 30 deg and 45 deg were designed. The blockage ratios were adjusted from 0 to 20%. The results indicated the blockage could enhance the penetration of film cooling flow to the mainstream. Thus, the averaged effectiveness and coolant coverage area were reduced. Moreover, the pressure loss inside of the hole was increased. With the increase of BR, the decrement of film cooling effectiveness caused by blockage rapidly increased. At BR = 1.5, the decrement could be acquired up to 70% for a blockage ratio of 20%. The decrement of film cooling effectiveness caused by blockage was nearly nonsensitive to the injection angle; however, the larger angle could generate the higher increment of pressure loss caused by blockage. A new design method for the couple scheme of film cooling and TBC was proposed, i.e., increasing the inlet diameter according to the blockage ratio before TBC spraying. In comparison with the original unblocked-hole, the enlarged blocked-hole not only kept the nearly same area-averaged effectiveness but also reduced slightly the pressure loss inside of the hole. Unfortunately, application of enlarged blocked-hole at large BR could lead to a more obvious reduction of effectiveness near hole-exit, in comparison with the original common-hole.

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