Experimental and Computational Evaluation of Flow Characteristics for Advanced Film Cooling Hole Geometries

2013 ◽  
Author(s):  
David Gomez-Ramirez ◽  
Shreyas Srinivasan ◽  
Sridharan Ramesh ◽  
Marco Miranda ◽  
Srinath V. Ekkad ◽  
...  
Keyword(s):  
Flat Plate ◽  
Film Cooling ◽  
Gas Turbines ◽  
Structural Integrity ◽  
Fluid Dynamic ◽  
Vortex Formation ◽  
Flow Characteristics ◽  
Cooling Effectiveness ◽  
Computational Evaluation ◽  
Cylindrical Holes

Film cooling is crucial in the field of gas turbines to protect the blade surfaces from the hot combustion gases. Several hole geometries have been studied in the past in an effort to optimize the cooling effectiveness of the holes while maintaining the structural integrity of the blade and low manufacturing costs. To understand the cooling effectiveness of the various hole geometries, the flow structures that develop as the coolant jet interacts with the hot mainstream must be understood. The present paper compares the results obtained from 2D Particle Image Velocimetry (PIV) measurements with CFD predictions using standard Reynolds-Averaged Navier Stokes (RANS) models with a commercially available code. The study is conducted for flat plate film cooling via conventional cylindrical holes, shaped holes (10° flare/laidback), and a tripod anti-vortex hole (AV) design. A constant blowing ratio (BR) of 0.5 was used for all the experiments, except for an additional measurement for the AV design at a BR of 1.0. Computational fluid dynamic (CFD) calculations were made with a standard k-epsilon model and compared to PIV results. The results show the counter-rotating vortices developing for cylindrical and shaped holes up to 5D and 3D respectively from the hole exit. AV holes showed no vortex formation, further supporting its higher cooling performance. Moreover, the present results indicate no separation of the coolant jet for AV or shaped holes as expected, while cylindrical holes displayed a small separation with a vertical extent of ∼0.1D. The CFD model was able to capture the main structures of the flow, but further efforts will concentrate in improving the representation of the flow normal to the flat plate surface.

Effect of Density Ratio on Film-Cooling Effectiveness Distribution and Its Uniformity for Several Hole Geometries on a Flat Plate

2019 ◽  
Vol 141 (5) ◽  
Author(s):  
Jiaxu Yao ◽  
Jin Xu ◽  
Ke Zhang ◽  
Jiang Lei ◽  
Lesley M. Wright
Keyword(s):  
Flat Plate ◽  
Film Cooling ◽  
Density Ratio ◽  
Lateral Spread ◽  
Spanwise Direction ◽  
Cooling Effectiveness ◽  
Film Cooling Effectiveness ◽  
Cylindrical Holes ◽  
Density Ratios ◽  
Compound Angle

The film cooling effectiveness distribution and its uniformity downstream of a row of film cooling holes on a flat plate are investigated by pressure sensitive paint (PSP) under different density ratios. Several hole geometries are studied, including streamwise cylindrical holes, compound-angled cylindrical holes, streamwise fan-shape holes, compound-angled fan-shape holes, and double-jet film-cooling (DJFC) holes. All of them have an inclination angle (θ) of 35 deg. The compound angle (β) is 45 deg. The fan-shape holes have a 10 deg expansion in the spanwise direction. For a fair comparison, the pitch is kept as 4d for the cylindrical and the fan-shape holes, and 8d for the DJFC holes. The uniformity of effectiveness distribution is described by a new parameter (Lateral-Uniformity, LU) defined in this paper. The effects of density ratios (DR = 1.0, 1.5 and 2.5) on the film-cooling effectiveness and its uniformity are focused. Differences among geometries and effects of blowing ratios (M = 0.5, 1.0, 1.5, and 2.0) are also considered. The results show that at higher density ratios, the lateral spread of the discrete-hole geometries (i.e., the cylindrical and the fan-shape holes) is enhanced, while the DJFC holes is more advantageous in film-cooling effectiveness. Mostly, a higher lateral-uniformity is obtained at DR = 2.5 due to better coolant coverage and enhanced lateral spread, but the effects of the density ratio on the lateral-uniformity are not monotonic in some cases. Utilizing the compound angle configuration leads to an increased lateral-uniformity due to a stronger spanwise motion of the jet. Generally, with a higher blowing ratio, the lateral-uniformity of the discrete-hole geometries decreases due to narrower traces, while that of the DJFC holes increases due to a stronger spanwise movement.

Film Cooling Effectiveness From Two Rows of Compound Angled Cylindrical Holes Using Pressure-Sensitive Paint Technique

2019 ◽  
Vol 141 (4) ◽  
Author(s):  
Nian Wang ◽  
Mingjie Zhang ◽  
Chao-Cheng Shiau ◽  
Je-Chin Han
Keyword(s):  
Flat Plate ◽  
Film Cooling ◽  
Density Ratio ◽  
Pressure Sensitive Paint ◽  
Cooling Effectiveness ◽  
Film Cooling Effectiveness ◽  
Blowing Ratio ◽  
Pressure Sensitive ◽  
Staggered Arrangement ◽  
Cylindrical Holes

This study investigates the effects of blowing ratio, density ratio, and spanwise pitch on the flat plate film cooling from two rows of compound angled cylindrical holes. Two arrangements of two-row compound angled cylindrical holes are tested: (a) the first row and the second row are oriented in staggered and same compound angled direction (β = +45 deg for the first row and +45 deg for the second row); (b) the first row and the second row are oriented in inline and opposite direction (β = +45 deg for the first row and −45 deg for the second row). The cooling hole is 4 mm in diameter with an inclined angle of 30 deg. The streamwise row-to-row spacing is fixed at 3d, and the spanwise hole-to-hole (p) is varying from 4d, 6d to 8d for both designs. The film cooling effectiveness measurements were performed in a low-speed wind tunnel in which the turbulence intensity is kept at 6%. There are 36 cases for each design including four blowing ratios (M = 0.5, 1.0, 1.5, and 2.0), three density ratios (DR = 1.0, 1.5, and 2.0), and three hole-to-hole spacing (p/d = 4, 6, and 8). The detailed film cooling effectiveness distributions were obtained by using the steady-state pressure-sensitive paint (PSP) technique. The spanwise-averaged cooling effectiveness are compared over the range of flow parameters. Some interesting observations are discovered including blowing ratio effect strongly depending on geometric design; staggered arrangement of the hole with same orientation does not yield better effectiveness at higher blowing ratio. Currently, film cooling effectiveness correlation of two-row compound angled cylindrical holes is not available, so this study developed the correlations for the inline arrangement of holes with opposing angles and the staggered arrangement of holes with same angles. The results and correlations are expected to provide useful information for the two-row flat plate film cooling analysis.

The NEKOMIMI Cooling Technology: Cooling Holes With Ears for High-Efficient Film Cooling

2011 ◽  
Author(s):  
Karsten Kusterer ◽  
Anas Elyas ◽  
Dieter Bohn ◽  
Takao Sugimoto ◽  
Ryozo Tanaka ◽  
...  
Keyword(s):  
Film Cooling ◽  
Gas Turbines ◽  
Experimental Investigations ◽  
Cooling Effectiveness ◽  
Film Cooling Effectiveness ◽  
High Efficient ◽  
Cylindrical Holes ◽  
Cooling Technology ◽  
Lift Off ◽  
Cooling Air

Further improvement of the thermal efficiency of modern gas turbines can be achieved by a further reduction of the cooling air amount. Therefore, it is necessary to increase the cooling effectiveness, so that the available cooling air fulfils the cooling task even if the amount has been reduced. Due to experimental and numerical efforts, it is well understood today that aerodynamic mixing processes are enhanced by counter-rotating vortices (CRV) in the cooling jets and lead to jet lift-off effects. Thus, the film-cooling effectiveness is reduced soon behind the cooling air ejection through the holes. Due to that basic understanding, different technologies for improving film cooling have been developed. Some of them focus on establishing anti-counter-rotating vortices (ACRV) inside the cooling jet that prevent the hot gas from flowing underneath the jet and, thus, avoid the lift-off effect. One of these technologies is the double-jet film cooling (DJFC), invented by the authors, where the special arrangement of two cylindrical holes lead to a cooling jet with such an anti-vortex system. However, beside the advantage that the holes are simple cylindrical holes, one disadvantage is that appropriate supply with cooling air for both holes is sometimes difficult to be established in real configurations. Thus, the authors have followed the idea to transfer the original double-jet film cooling principle to a special configuration with merged holes. Thus, in that case only one air supply is necessary but the anti-vortex effect has been preserved. The derived cooling technology has been named NEKOMIMI technology. The paper explains the principle of that technology. Results from experimental investigations including film cooling effectiveness measurements for the new technology are presented. The results are compared to conventional cooling hole configurations showing the tremendous positive effect in reaching highest film cooling effectiveness for the new configuration at M = 1.5 and partly for M = 1. Numerical investigations for the M = 1.5 case indicate that the existence of the ACRV is the likely reason for the enhanced cooling performance of the new configuration.

Effect of Density Ratio on Flat Plate Film Cooling With Shaped Holes Using PSP

2010 ◽  
Author(s):  
Lesley M. Wright ◽  
Stephen T. McClain ◽  
Michael D. Clemenson
Keyword(s):  
Flat Plate ◽  
Turbulence Intensity ◽  
Film Cooling ◽  
Density Ratio ◽  
Freestream Turbulence ◽  
Cooling Effectiveness ◽  
Film Cooling Effectiveness ◽  
Blowing Ratio ◽  
Cylindrical Holes ◽  
Film Cooling Holes

Detailed film cooling effectiveness distributions are obtained on a flat plate using the pressure sensitive paint (PSP) technique. The applicability of the PSP technique is expanded to include a coolant-to-mainstream density ratio of 1.4. The effect of density ratio on the film cooling effectiveness is coupled with varying blowing ratio (M = 0.25–2.0), freestream turbulence intensity (Tu = 1%–12.5%), and film hole geometry. The effectiveness distributions are obtained on three separate flat plates containing either simple angle, cylindrical holes, simple angle, fanshaped holes (α = 10°), or simple angle, laidback, fanshaped holes (α = 10°, γ = 10°). In all three cases, the film cooling holes are angled at θ = 35° from the mainstream flow. Using the PSP technique, the combined effects of blowing ratio, turbulence intensity, and density ratio are captured for each film cooling geometry. The detailed film cooling effectiveness distributions, for cylindrical holes, clearly show the effectiveness at the lowest blowing ratio is enhanced at the lower density ratio (DR = 1). However, as the blowing ratio increases, a transition occurs, leading to increased effectiveness with the elevated density ratio (DR = 1.4). In addition, the PSP technique captures an upstream shift of the coolant jet reattachment point as the density ratio increases or the turbulence intensity increases (at moderate blowing ratios for cylindrical holes). With the decreased momentum of the shaped film cooling holes, the greatest film cooling effectiveness is obtained at the lower density ratio (DR = 1.0) over the entire range of blowing ratios considered. In all cases, as the freestream turbulence intensity increases, the film effectiveness decreases; this effect is reduced as the blowing ratio increases for all three film hole configurations.

Film Cooling Effectiveness From Two-Row of Compound Angled Cylindrical Holes Using PSP Technique

2018 ◽  
Author(s):  
Nian Wang ◽  
Mingjie Zhang ◽  
Chao-Cheng Shiau ◽  
Je-Chin Han
Keyword(s):  
Flat Plate ◽  
Film Cooling ◽  
Density Ratio ◽  
Cooling Effectiveness ◽  
Film Cooling Effectiveness ◽  
Free Stream Turbulence ◽  
Cooling Hole ◽  
Cylindrical Holes ◽  
Inclined Angle ◽  
Density Ratios

This study investigates the combined effects of blowing ratio and density ratio on flat plate film cooling effectiveness from two-row of compound angled cylindrical holes. Two arrangements of two-row compound angled cylindrical holes are tested: the first row and second row are oriented in staggered but same compound angled direction (β = +45° for the first row, +45° for the second row); the first row and second row are oriented in inline but opposite direction (β = +45° for the first row, −45° for the second row). Each cooling hole is 4 mm in diameter with an inclined angle 30°. The streamwise distance between the two rows is fixed at 4d and the spanwise pitch between the two holes (p) is 4d, 6d, and 8d, respectively. The experiments are performed at four blowing ratios (M = 0.5, 1.0, 1.5, 2.0) and three density ratios (DR = 1.0, 1.5, 2.0). The free stream turbulence intensity is kept at 6%. Detailed film cooling effectiveness distributions are obtained using the steady state pressure-sensitive paint (PSP) technique. The detailed film cooling effectiveness contours are presented and the spanwise averaged film effectiveness results are compared over the range of flow parameters. Film cooling effectiveness correlations are developed for both inline and staggered compound angled cylindrical holes. The results provide baseline information for the flat plate film cooling analysis with two-row of compound angled cylindrical holes.

Numerical Simulation of Hole Shapes Effect on Film Cooling Effectiveness and Aerodynamics Loss over Flat Plate

2012 ◽  
Vol 614-615 ◽  
pp. 216-221 ◽  
Author(s):  
Ruo Ling Dong ◽  
Hong Hui Shi ◽  
Wei Chen ◽  
Xiao Dong Zhang
Keyword(s):  
Numerical Simulation ◽  
Flat Plate ◽  
Film Cooling ◽  
Flow Characteristics ◽  
Low Loss ◽  
Simple Method ◽  
Cooling Effectiveness ◽  
Film Cooling Effectiveness ◽  
Blowing Ratio ◽  
Compound Angle

A numerical simulation was conducted to investigate the flow characteristics, film cooling effectiveness and aerodynamics loss over flat plate. Three types of shaped holes, separately, cylindrical hole, laterally diffused hole and converging-expanding hole were studied with 35°inclination angle and 0°compound angle. The inlet diameter of the hole in this paper is 12.7 mm, giving a L/D ratio of 3.5 at a mainstream velocity of 20m/s, turbulence intensity 2%, and temperature ratio to cooling jet 1.97, with blowing ratio M equaling to 0.5. Realizable k-ε turbulence model, standard wall function and SIMPLE method for pressure-velocity coupling were used .The coefficients η and ξ were calculated to analyze cooling effectiveness and aerodynamics loss. Both high film cooling effectiveness and low loss are found with laterally diffused hole. While optimizing the hole geometry in film cooling, cooling effectiveness and aerodynamics loss should been considered simultaneously.

Effect of Density Ratio on Flat Plate Film Cooling With Shaped Holes Using PSP

2011 ◽  
Vol 133 (4) ◽  
Author(s):  
Lesley M. Wright ◽  
Stephen T. McClain ◽  
Michael D. Clemenson
Keyword(s):  
Flat Plate ◽  
Turbulence Intensity ◽  
Film Cooling ◽  
Density Ratio ◽  
Freestream Turbulence ◽  
Cooling Effectiveness ◽  
Film Cooling Effectiveness ◽  
Blowing Ratio ◽  
Cylindrical Holes ◽  
Film Cooling Holes

Detailed film-cooling effectiveness distributions are obtained on a flat plate using the pressure sensitive paint (PSP) technique. The applicability of the PSP technique is expanded to include a coolant-to-mainstream density ratio of 1.4. The effect of density ratio on the film-cooling effectiveness is coupled with varying blowing ratio (M=0.25–2.0), freestream turbulence intensity (Tu=1–12.5%), and film hole geometry. The effectiveness distributions are obtained on three separate flat plates containing either simple angle, cylindrical holes, simple angle, fanshaped holes (α=10 deg), or simple angle, laidback, fanshaped holes (α=10 deg and γ=10 deg). In all three cases, the film-cooling holes are angled at θ=35 deg from the mainstream flow. Using the PSP technique, the combined effects of blowing ratio, turbulence intensity, and density ratio are captured for each film-cooling geometry. The detailed film-cooling effectiveness distributions, for cylindrical holes, clearly show that the effectiveness at the lowest blowing ratio is enhanced at the lower density ratio (DR=1). However, as the blowing ratio increases, a transition occurs, leading to increased effectiveness with the elevated density ratio (DR=1.4). In addition, the PSP technique captures an upstream shift of the coolant jet reattachment point as the density ratio increases or the turbulence intensity increases (at moderate blowing ratios for cylindrical holes). With the decreased momentum of the shaped film-cooling holes, the greatest film-cooling effectiveness is obtained at the lower density ratio (DR=1.0) over the entire range of blowing ratios considered. In all cases, as the freestream turbulence intensity increases, the film effectiveness decreases; this effect is reduced as the blowing ratio increases for all three film hole configurations.

Numerical Predictions of Flow Structures and Film Cooling Effectiveness Values of a Turbine Vane: Effects of Secondary Holes

2019 ◽  
Author(s):  
Rui Zhu ◽  
Terrence W. Simon ◽  
Gongnan Xie
Keyword(s):  
Film Cooling ◽  
Gas Turbines ◽  
Suction Side ◽  
Pressure Side ◽  
Cooling Effectiveness ◽  
Cooling Performance ◽  
Film Cooling Effectiveness ◽  
Single Row ◽  
Cylindrical Holes ◽  
Better Than

Abstract In modern gas turbines, film cooling is the most common and efficient way to provide thermal protection for hot components. Secondary holes to a primary film cooling hole are used to improve film cooling performance by creating anti-kidney vortices, a technique that has been well documented using flat plate models. This study aims to evaluate the effects of secondary holes on film cooling effectiveness over an airfoil. The film cooling performance and flow fields of a row of primary holes with secondary holes on the pressure side and suction side of a C3X vane are numerically investigated and compared with the results of a single row of cylindrical holes and two rows of staggered cylindrical holes. Cases with different blowing ratios are analyzed. It is shown from the simulation that film cooling effectiveness of primary holes with secondary holes is much better than with a single row of cylindrical holes, and slightly better than with two rows of staggered holes on both pressure side and suction side, with the same amount of coolant usage and blowing ratio. The enhancement is higher on the pressure side than on the suction side. The results show that adding secondary holes can enhance film cooling effectiveness by creating anti-kidney vortices, which will weaken jet lift-off from the primary holes caused by the kidney vortex pair, especially at higher blowing ratios. In addition, film coverage of primary holes with secondary holes is wider and persists further downstream than for a single row of cylindrical holes.

An Experimental Study of Mist Film Cooling With Fan-Shaped Holes on an Extended Flat Plate: Part 1 — Heat Transfer

2014 ◽  
Author(s):  
Reda Ragab ◽  
Ting Wang
Keyword(s):  
Heat Transfer ◽  
Flat Plate ◽  
Film Cooling ◽  
Flow Behavior ◽  
Test Facility ◽  
Controlled Cooling ◽  
Cooling Effectiveness ◽  
Film Cooling Effectiveness ◽  
Cylindrical Holes ◽  
Cooling Effects

Motivated by the need to further improve film cooling in terms of both cooling effectiveness and coolant coverage area, the mist/air film cooling scheme is investigated through experiments using fan-shaped holes over an extended downstream length in this study. Both an existing wind tunnel and test facility, used in previous work, have been retrofitted. The first modification was extending the length of the flat plate test section to cover longer distances downstream of the injection holes, up to X/D = 100, in order to investigate whether mist cooling can be harnessed farther downstream where single-phase film cooling is not effective. The second modification was to incorporate a fan-shaped diffusion hole geometry in order to investigate whether mist can further enhance the film cooling performance of the already highly effective fan-shaped holes. A Phase Doppler Particle Analyzer (PDPA) system is employed to measure droplet size, velocity, and turbulence information. An infrared camera and thermocouples are both used for temperature measurements. Part 1 is focused on the heat transfer result on the wall, and Part 2 is focused on the two-phase droplet multiphase flow behavior. Three blowing ratios are investigated. The results show that, at low blowing ratios when the film is attached to the surface, the enhancement of the mist film cooling effectiveness, compared to the air-only case, on the centerline of the hole ranges from 40% in the near hole region to over 170% at X/D = 100. Due to the diffusive nature of the fan-shaped hole, the laterally-averaged enhancement is on par with that on the centerline. The significant enhancement over the extended downstream distance from X/D = 40–100 is attributed to the evaporation time needed to evaporate all of the droplets. Each droplet acts as a cooling sink and flies over a distance before it completely vaporizes. This “distributed cooling” characteristic allows controlled cooling by manipulating the size distribution of the water droplets to extend the cooling effects of the droplets farther downstream from the injection location. At higher blowing ratios, when the cooling film is lifted off from the surface, the cooling enhancement drops below 40%. Although the enhancement in the near hole region X/D < 40 is about 20% lower than that achieved by using the cylindrical holes, the magnitudes of the mist adiabatic film cooling effectiveness using fan-shaped holes are still much higher than those of the cylindrical holes.

Effect of multi-zone effusion cooling on an adiabatic flat plate for gas turbine application

2021 ◽  
Vol 0 (0) ◽  
Author(s):  
Ved Prakash ◽  
Sunil Chandel ◽  
Dineshsingh G. Thakur ◽  
Mukesh Prakash Mishra ◽  
R. K. Mishra
Keyword(s):  
Numerical Analysis ◽  
Flat Plate ◽  
Film Cooling ◽  
Velocity Ratio ◽  
Three Dimensional ◽  
Perforated Plate ◽  
Primary Flow ◽  
Cooling Effectiveness ◽  
Film Cooling Effectiveness ◽  
Cylindrical Holes

Abstract The present study performed a three-dimensional numerical analysis on an adiabatic flat plate with forward injection holes for multi-zone film cooling. The cooling holes were divided into three-zone, and the cold air was supplied from cylindrical holes at a velocity ratio of 0.5 and 1.5 with 30° inclination to the primary flow. The effect of multi-zone arrangement in film cooling effectiveness is studied, and a comparison between two-zone and three-zone arrangement has been made. Results show that the three-zone arrangement helps achieve better film cooling effectiveness than the two-zone arrangement due to the uniform flow of coolant at a higher velocity ratio. It also reduces the mass flow rate of secondary flow by decreasing the number of cylindrical holes in the perforated plate.

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