Experimental and Numerical Study on Effects of Turbulence Promoters on Flat Plate Film Cooling

2011 ◽  
Author(s):  
Eiji Sakai ◽  
Toshihiko Takahashi
Keyword(s):  
Flat Plate ◽  
Secondary Flow ◽  
Film Cooling ◽  
Numerical Study ◽  
Secondary Flows ◽  
Temperature Fields ◽  
Main Stream ◽  
Cooling Performance ◽  
Cooling Hole ◽  
Stream Lines

Turbulence promoters such as ribs inside turbine blade coolant channels are used to improve convective cooling but at the same time could influence external film cooling performance. The effects of rib orientation and rib position on film cooling performance are experimentally and numerically studied with a flat plate configuration in which external (main) flow and internal (secondary) flow are oriented perpendicular to each other. In the experiment, temperature fields are measured by thermo-couples varying blowing ratio at constant Reynolds number of main and secondary flows. To obtain detailed information about flow fields, Reynolds Averaged Navier Stokes (RANS) simulation and Detached Eddy Simulation (DES) are also performed using a commercial code Fluent. Temperature measured shows that rib orientation has a strong influence on film effectiveness. With forward-oriented ribs, higher film effectiveness is observed compared to the reference case without ribs. On the contrary with inverse-oriented ribs, lower film effectiveness is observed. The difference comes from the flow structure in the film cooling hole. With the forward-oriented ribs, straight stream lines are observed in the cooling hole, while with the inverse-oriented ribs, helical stream lines are observed. Due to the helical stream lines in the hole, ejection angle of the secondary flow to the main stream becomes large, resulting in so called lift-off and lower film effectiveness.

An Experimental Investigation of an Anti-Vortex Film Cooling Geometry Under Low and High Turbulence Conditions

2012 ◽  
Author(s):  
Sebastian Schulz ◽  
Simon Maier ◽  
Jeffrey P. Bons
Keyword(s):  
Flat Plate ◽  
Secondary Flow ◽  
Infrared Thermography ◽  
Film Cooling ◽  
Streamwise Direction ◽  
Cooling Effectiveness ◽  
Cooling Performance ◽  
Film Cooling Effectiveness ◽  
Cooling Hole ◽  
High Turbulence

In an attempt to abate the detrimental jet vorticity and lift-off effects at high blowing ratios, the objective of the present study is to investigate the impact of an anti-vortex film cooling hole design on the film cooling effectiveness and the secondary flow field. Furthermore, the influence of low and high turbulence levels is studied with Tu ≈ .0.7% and ≈ 10%, respectively. For the experiments infrared thermography and particle image velocimetry (PIV) are employed. The experiments are conducted in a subsonic wind tunnel at a Reynolds number of 11000 based on the film cooling hole diameter. A flat plate model with an array of three cylindrical primary holes with secondary offshoots to each side represents the anti-vortex geometry. The cylindrical hole arrangement with a diameter of 17.5 mm is inclined at 30° in streamwise direction, with the anti-vortex holes branching off from the primary hole base in a 21° angle. Information from a flat plate with six cylindrical holes of 17.5 mm in diameter inclined at 30 in streamwise direction is used as baseline for comparison. The primary hole spacing was 4.75 and 3 hole diameters, respectively. Results are presented for blowing ratios of 1 and 2 with a constant density ratio of 1.1. The PIV measurements are taken in two planes perpendicular to the flow direction to record the secondary flow structures. The results of the infrared thermography show a strong decrease in film cooling effectiveness as high turbulence levels occur, especially for low blowing ratios. For higher blowing ratios low and high turbulence levels have similar effects on film cooling effectiveness. A significant improvement in film cooling performance is displayed by the anti-vortex design over the standard circular hole arrangement for every blowing ratio. The effectiveness results reveal an improved lateral spreading of the coolant with coolant jets staying attached throughout the series of experiments. By remaining inside the boundary layer, the effects of a high turbulent freestream on film cooling performance is less. The PIV results unveil information of a new vortex pair on either side of the primary hole kidney vortex. Especially at high blowing ratios the results indicate, that the anti-vortex hole design promotes the interaction between the vortical structures, explaining the increased lateral film effectiveness results. The factor which lends to the superior performance and credibility of the studied anti-vortex design is that the results are obtained for 35% less mass flow than the baseline.

Injection Angle Influence of Secondary Holes on the Enhancement of Film Cooling Effectiveness With Horn-Shaped or Cylindrical Primary Holes

2017 ◽  
Author(s):  
Rui Zhu ◽  
Gongnan Xie ◽  
Terrence W. Simon
Keyword(s):  
Film Cooling ◽  
Numerical Study ◽  
Cylindrical Hole ◽  
Cooling Effectiveness ◽  
Cooling Performance ◽  
Film Cooling Effectiveness ◽  
Injection Angle ◽  
Inclination Angles ◽  
Cooling Hole ◽  
Cylindrical Holes

Secondary holes to a main film cooling hole are used to improve film cooling performance by creating anti-kidney vortices. The effects of injection angle of the secondary holes on both film cooling effectiveness and surrounding thermal and flow fields are investigated in this numerical study. Two kinds of primary hole shapes are adopted. One is a cylindrical hole, the other is a horn-shaped hole which is designed from a cylindrical hole by expanding the hole in the transverse direction to double the hole size at the exit. Two smaller cylindrical holes, the secondary holes, are located symmetrically about the centerline and downstream of the primary hole. Three compound injection angles (α = 30°, 45° and 60°, β = 30°) of the secondary holes are analyzed while the injection angle of the primary hole is kept at 45°. Cases with various blowing ratios are computed. It is shown from the simulation that cooling effectiveness of secondary holes with a horn-shaped primary hole is better than that with a cylindrical primary hole, especially at high blowing ratios. With a cylindrical primary hole, increasing inclination angle of the secondary holes provides better cooling effectiveness because the anti-kidney vortices created by shallow secondary holes cannot counteract the kidney vortex pairs adequately, enhancing mixing of main flow and coolant. For secondary holes with a horn-shaped primary hole, large secondary hole inclination angles provide better cooling performance at low blowing ratios; but, at high blowing ratios, secondary holes with small inclination angles are more effective, as the film coverage becomes wider in the downstream area.

Improvement of Flat-Plate Film Cooling Performance by Double Flow Control Devices: Part I — Investigations on Capability of a Base-Type Device

2014 ◽  
Author(s):  
Ken-ichi Funazaki ◽  
Ryota Nakata ◽  
Hirokazu Kawabata ◽  
Hisato Tagawa ◽  
Yasuhiro Horiuchi
Keyword(s):  
Flow Control ◽  
Flat Plate ◽  
Film Cooling ◽  
Laser Doppler Velocimeter ◽  
Pressure Probe ◽  
Cooling Performance ◽  
Flow Control Devices ◽  
Type Device ◽  
Cooling Hole ◽  
Control Devices

This paper deals with effects of double flow control devices (DFCDs) on flat plate film cooling performance. Aiming for further improvement of film effectiveness of discrete cooling holes, this new type of controlling method is invented and recently patented by the authors. The performance of base-type DFCDs, installed just upstream of cooling holes with conventional round or fan-shaped exits, is thoroughly investigated and reported in this study. Effects of the hole pitch are examined. Three hole-pitch cases, 3.0d, 4.5 d and 6.0 d are examined in this study to explore a possibility of reducing the cooling air by the application of DFCDs, where d is a hole diameter. In order to investigate the film effectiveness, a transient method using a high-resolution infrared camera is adopted. At the downstream of the cooling hole, the time-averaged temperature field is captured by a thermocouple rake and the time-averaged velocity field is captured by 3D Laser Doppler Velocimeter (LDV), respectively. Furthermore, the aerodynamic loss characteristics of the cooling hole with and without DFCDs are measured by a total pressure probe rake. The experiments are carried out for two blowing ratios, 0.5 and 1.0. It is found that DFCDs are quite effective in increasing the film effectiveness not only for round but also the fan-shaped holes. Starting from the base-type device, a robust optimization using Taguchi Method has been made by the present authors and will be reported as Part II.

Numerical Evaluation of Surface Roughness Effects on Film-Cooling Performance in a Laidback Fan-Shaped Hole

2020 ◽  
Author(s):  
Ali Zamiri ◽  
Sung Jin You ◽  
Jin Taek Chung
Keyword(s):  
Surface Roughness ◽  
Flat Plate ◽  
Film Cooling ◽  
Density Ratio ◽  
Roughness Height ◽  
Constant Density ◽  
Cooling Performance ◽  
Cooling Hole ◽  
Shaped Hole ◽  
Grain Roughness

Abstract This study numerically investigates the influences of cooling hole surface roughness in a laidback fan-shaped hole on the flow structure and film-cooling effectiveness. The three-dimensional compressible LES approach (large eddy simulation) is conducted in a baseline 7-7-7 laidback fan-shaped hole. The cooling hole is located on a flat plate surface with a 30-degree injection angle at a constant density ratio DR = 1.5 and two blowing ratios M = 1.5 and 3. The computational results were validated by the measurements in terms of velocity and thermal fields for both the smooth and rough holes. In order to numerically consider the influences of the surface roughness on cooling hole side, the equivalent sand grain roughness method was utilized. Different correlations between the equivalent sand grain roughness height and arithmetic average roughness height were numerically tested to find an accurate correlation in comparison to the measurements. The computational data revealed that the surface roughness of the hole interior walls increases the thickness of the boundary layers within the hole. This leads to a higher jet core flow at the hole exit and lower film-cooling performance at the surface of flat plate compared to those of the smooth cooling hole. The minimum area-averaged film-cooling performance was observed in the case of the highest blowing ratio and the largest surface roughness height. The present work reveals that the current LES approach by considering the proper equivalent sand grain roughness height is a powerful tool to obtain the accurate solution in the prediction of the heat transfer characteristics and the flow structures in the fan-shaped cooling holes.

Effects of Pin-Fin Shapes on Mesh-Fed Slot Film Cooling for a Flat-Plate Model

2019 ◽  
Vol 11 (3) ◽  
Author(s):  
Xiao-Ming Tan ◽  
Jing-Zhou Zhang ◽  
Qing-Zhi Cai
Keyword(s):  
Flat Plate ◽  
Film Cooling ◽  
Coolant Flow ◽  
Plate Model ◽  
Cross Sectional ◽  
Cooling Performance ◽  
Pin Fin ◽  
Pin Fins ◽  
Cooling Hole ◽  
Slot Film Cooling

Experimental and numerical research is performed to illustrate the effects of pin-fin shapes on mesh-fed slot film cooling performance on a flat-plate model. Three types of pin-fin shapes (such as circular, elliptical, and drop-shaped) with the same cross-sectional area are taken into consideration. The results show that a pair of counter rotating vortices is still generated for the mesh-fed slot film cooling scheme due to the strong “jetting” effect of coolant flow at the slot outlet. As the coolant jet ejecting from mesh-fed slot is capable of establishing more uniform film layer over the protected surface, the kidney vortices are illustrated to have weakly detrimental role on the film cooling performance. By the shaping of pin fins, the uniformity of coolant flow exiting mesh-fed slot is improved in comparison to the baseline case of circular shape, especially for the elliptical-shape pin-fin array. Therefore, the jetting effect of coolant flow is alleviated for the elliptical and drop-shaped pin-fin meshes when compared to the circular pin-fin mesh. In general, the pin-fin shape has nearly no influence on cooling effectiveness immediately downstream the film cooling-hole outlet. However, beyond x/s = 5, the elliptical and drop-shaped pin fins are demonstrated to be advantageous over the circular pin fins.

Numerical Analysis of Film-Cooling Performance and Optimization for a Novel Shaped Film-Cooling Hole

2012 ◽  
Author(s):  
Ki-Don Lee ◽  
Sun-Min Kim ◽  
Kwang-Yong Kim
Keyword(s):  
Film Cooling ◽  
Numerical Study ◽  
Density Ratio ◽  
Lateral Spreading ◽  
Diameter Ratio ◽  
The Novel ◽  
Cooling Performance ◽  
Cooling Hole ◽  
Shaped Hole ◽  
Film Cooling Holes

In the present work, a numerical study on a novel shaped film-cooling hole has been performed. The novel shaped hole is designed to enhance lateral spreading of coolant on the cooling surface. The film-cooling performance of the novel shaped hole is compared with the fan, laidback fan, and dumbbell shaped film-cooling holes at density ratio of 1.75 in the range of blowing ratio from 0.5 to 2.5. The optimization of the novel shaped hole has been carried out to increase film-cooling effectiveness with four design variables, i.e., lateral expansion of the diffuser, forward expansion angle of the hole, length to diameter ratio of the hole, and pitch to diameter ratio of the hole. To optimize the hole shape, the radial basis neural network model is constructed and sequential quadratic programming is used to find optimal point from the surrogate model. The novel shaped hole shows remarkably improved film-cooling performance in comparison with the other film-cooling holes. The novel shaped hole modified by the optimization gives enhanced performance in comparison with the reference geometry.

Numerical Investigation of Film Cooling Performance With Different Internal Flow Structures

2014 ◽  
Author(s):  
Jianxia Luo ◽  
Cunliang Liu ◽  
Huiren Zhu
Keyword(s):  
Secondary Flow ◽  
Film Cooling ◽  
Internal Flow ◽  
Navier Stokes ◽  
Flow Structures ◽  
Cooling Performance ◽  
Smooth Case ◽  
Air Jet ◽  
Smooth Channel ◽  
Cooling Hole

Four coolant channel configurations, including supply plenum without crossflow, smooth channel with crossflow and ribbed channels with crossflow ( 135° and 45° angled ribs), are simulated to find out the effect of internal flow structures on the external film cooling performance. Reynolds Averaged Navier Stokes (RANS) simulations with realizable k-ε turbulence model and enhanced wall treatment are performed using a commercial code Fluent. Blowing ratios cover a range from 0.5 to 2.0. For the three cases with crossflow, a constant Reynolds number, ReDh, is fixed as 100000. Particular attention has been paid to the flow structures and counter-rotating vortices. Helical motion of secondary flow is observed in the hole of the smooth case and the 45° ribs case, inducing strong velocity separation in the cooling hole and blocks at the entrance and exit. In the two cases, the cooling-air jet divides into two parts after being blown out of the hole and a pair of skewed vortices appears downstream. In the 135° ribs case, the vortex in the upper half region of the secondary flow channel rotates in the same direction with the hole inclination direction, the straight stream lines are generated and therefore lower loss and higher discharge coefficient. Experimental data of the smooth case and the 135° ribs case show the good agreement with the numerical results.

Effects of Endwall 3D Contouring on Film Cooling Effectiveness of Cylindrical Hole Injections at Different Locations on Vane Endwall

2018 ◽  
Author(s):  
Pingting Chen ◽  
Hongyu Gao ◽  
Xueying Li ◽  
Jing Ren ◽  
Hongde Jiang
Keyword(s):  
Secondary Flow ◽  
Film Cooling ◽  
Guide Vane ◽  
Density Ratio ◽  
Secondary Flows ◽  
Cylindrical Hole ◽  
Cooling Effectiveness ◽  
Cooling Performance ◽  
Film Cooling Effectiveness ◽  
Endwall Contouring

With the development of gas turbine, the secondary flow loss in vane passage is getting higher. To reduce the strength of secondary flows within vane passage, endwall 3D contouring is an effective design. Endwall 3D contouring can lead to significant changes in the secondary flow vortices, which lead to changes on jet-to-secondary flow interaction and then changes on the film cooling effectiveness. Meanwhile, the geometry configuration of the contoured endwall, such as the rising and falling on the endwall, can also have an impact on film cooling performance. As a result, the film cooling performance on contoured endwall differs from that on flat endwall. Understanding the difference in film cooling characteristics on the contoured endwall and flat endwall may help to make better endwall contouring design and better endwall film cooling arrangement. The present experiment compares the film cooling effectiveness of cylindrical hole injections at different locations on 3D contoured endwall versus flat endwall in an NGV (nozzle guide vane) passage. The measurement is performed in a low speed wind tunnel with a F-class annular sector NGV cascade. The cylindrical hole injections are located as 4 different rows at −30% axial chord, 30% axial chord, 50% axial chord and 70% axial chord. Endwall pressure distribution is measured with pressure taps by pressure sensor while film cooling effectiveness is measured using PSP (Pressure Sensitive Paint). Two density ratios with 1.0 and 1.5 and several average blowing ratios are investigated. Effects of endwall contouring, density ratio and blowing ratio on film cooling effectiveness are obtained and the results are presented and explained in this investigation.

Experimental and Numerical Investigations of Effects of Flow Control Devices Upon Flat-Plate Film Cooling Performance

2013 ◽  
Vol 136 (6) ◽  
Author(s):  
Hirokazu Kawabata ◽  
Ken-ichi Funazaki ◽  
Ryota Nakata ◽  
Daichi Takahashi
Keyword(s):  
Flow Field ◽  
Flow Control ◽  
Flat Plate ◽  
Vortex Structure ◽  
Film Cooling ◽  
Pressure Probe ◽  
Cooling Performance ◽  
Flow Control Devices ◽  
Cooling Hole ◽  
Control Devices

This study deals with the experimental and numerical studies of the effect of flow control devices (FCDs) on the film cooling performance of a circular cooling hole on a flat plate. Two types of FCDs with different heights are examined in this study, where each of them is mounted to the flat plate upstream of the cooling hole by changing its lateral position with respect to the hole centerline. In order to measure the film effectiveness as well as heat transfer downstream of the cooling hole with upstream FCD, a transient method using a high-resolution infrared camera is adopted. The velocity field downstream of the cooling hole is captured by 3D laser Doppler velocimeter (LDV). Furthermore, the aerodynamic loss associated with the cooling hole with/without FCD is measured by a total pressure probe rake. The experiments are carried out at blowing ratios ranging from 0.5 to 1.0. In addition, numerical simulations are also made to have a better understanding of the flow field. LES approach is employed to solve the flow field and visualize the vortex structure around the cooling hole with FCD. When a taller FCD is mounted to the plate, the film effectiveness tends to increase due to the vortex structure generated by the FCD. As FCD is laterally shifted from the centerline, the film effectiveness increases, while the lift-off of cooling air is also promoted when FCD is put on the center line.

Experimental and Numerical Investigations of Effects of Flow Control Devices Upon Flat-Plate Film Cooling Performance

2013 ◽  
Author(s):  
Hirokazu Kawabata ◽  
Ken-ichi Funazaki ◽  
Ryota Nakata ◽  
Daichi Takahashi
Keyword(s):  
Flow Field ◽  
Flow Control ◽  
Flat Plate ◽  
Vortex Structure ◽  
Film Cooling ◽  
Pressure Probe ◽  
Cooling Performance ◽  
Flow Control Devices ◽  
Cooling Hole ◽  
Control Devices

This study deals with the experimental and numerical studies of the effect of flow control devices (FCDs) on the film cooling performance of a circular cooling hole on a flat plate. Two types of FCDs with different heights are examined in this study, where each of them is mounted to the flat plate upstream of the cooling hole by changing its lateral position with respect to the hole centerline. In order to measure the film effectiveness as well as heat transfer downstream of the cooling hole with upstream FCD, a transient method using a high-resolution infrared camera is adopted. The velocity field downstream of the cooling hole is captured by 3D Laser Doppler Velocimeter (LDV). Furthermore, the aerodynamic loss associated with the cooling hole with/without FCD is measured by a total pressure probe rake. The experiments are carried out at blowing ratios ranging from 0.5 to 1.0. In addition, numerical simulations are also made to have a better understanding of the flow field. LES approach is employed to solve the flow field and visualize the vortex structure around the cooling hole with FCD. When a higher FCD is mounted to the plate, the film effectiveness tends to increase due to the vortex structure generated by the FCD. As FCD is laterally shifted from the centerline, the film effectiveness increases, while the lift-off of cooling air is also promoted when FCD is put on the center line.

Sign in / Sign up

Export Citation Format

Share Document