Numerical Investigation of a Laser-Drilled Cooling Hole

2017 ◽  
Author(s):  
D. J. Cerantola ◽  
A. M. Birk
Keyword(s):  
Heat Transfer ◽  
Film Cooling ◽  
Average Height ◽  
Conical Nozzle ◽  
Film Cooling Effectiveness ◽  
Hole Area ◽  
Cooling Hole ◽  
Common Technique ◽  
Mass Flow Rates ◽  
Percussion Laser Drilling

Modern aeroengines utilized effusion cooling technology to further protect the components from degrading at the operating temperatures. Most studies did not address the influence of the manufacturing process used to form the cooling holes on the flow physics where percussion laser drilling was a common technique that produced irregularly shaped holes with roughened surfaces. The investigated as-drilled hole surface was statistically homogeneous, non-isotropic, and generally composed of gradually transitioning plateaus that had imperfections with an average height of 0.32 hole diameters. A conjugate heat transfer CFD study was completed on cylindrical, conical nozzle, and as-drilled holes, all yielding the same hole mass flow rates, with the realizable k-ε turbulence model at representative engine conditions. The cylindrical hole had higher film cooling effectiveness due to lower effluent velocity, and better in-hole heat transfer performance due to higher on-average in-hole flow velocities. The as-drilled hole had nominally better film cooling than the conical nozzle hole due to the higher in-hole turbulence production caused by the roughened surface texture. Ultimately, the hole area profile more significantly influenced the averaged metal temperature.

Film Cooling Measurements for a Laidback Fan-Shaped Hole: Effect of Coolant Crossflow on Cooling Effectiveness and Heat Transfer

2019 ◽  
Vol 141 (4) ◽  
Author(s):  
Marc Fraas ◽  
Tobias Glasenapp ◽  
Achmed Schulz ◽  
Hans-Jörg Bauer
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Film Cooling ◽  
Gas Flow ◽  
Density Ratio ◽  
Coolant Flow ◽  
Cooling Effectiveness ◽  
Film Cooling Effectiveness ◽  
Cooling Hole ◽  
Film Cooling Holes

Internal coolant passages of gas turbine vanes and blades have various orientations relative to the external hot gas flow. As a consequence, the inflow of film cooling holes varies as well. To further identify the influencing parameters of film cooling under varying inflow conditions, the present paper provides detailed experimental data. The generic study is performed in a novel test rig, which enables compliance with all relevant similarity parameters including density ratio. Film cooling effectiveness as well as heat transfer of a 10–10–10 deg laidback fan-shaped cooling hole is discussed. Data are processed and presented over 50 hole diameters downstream of the cooling hole exit. First, the parallel coolant flow setup is discussed. Subsequently, it is compared to a perpendicular coolant flow setup at a moderate coolant channel Reynolds number. For the perpendicular coolant flow, asymmetric flow separation in the diffuser occurs and leads to a reduction of film cooling effectiveness. For a higher coolant channel Reynolds number and perpendicular coolant flow, asymmetry increases and cooling effectiveness is further decreased. An increase in blowing ratio does not lead to a significant increase in cooling effectiveness. For all cases investigated, heat transfer augmentation due to film cooling is observed. Heat transfer is highest in the near-hole region and decreases further downstream. Results prove that coolant flow orientation has a severe impact on both parameters.

Numerical Investigation of Adiabatic and Conjugate Film Cooling Effectiveness on a Single Cylindrical Film-Cooling Hole

2004 ◽  
Author(s):  
Mahmood Silieti ◽  
Eduardo Divo ◽  
Alain J. Kassab
Keyword(s):  
Heat Transfer ◽  
Film Cooling ◽  
Conjugate Heat Transfer ◽  
Turbulence Models ◽  
Temperature Fields ◽  
Cooling Effectiveness ◽  
Film Cooling Effectiveness ◽  
Cooling Hole ◽  
Dimensional Distribution ◽  
Lift Off

This paper documents a computational investigation of the film-cooling effectiveness of a 3-D gas turbine endwall with one cylindrical cooling hole. The simulations were performed for an adiabatic and conjugate heat transfer models. Turbulence closure was investigated using five different turbulence models; the standard k-ε model, the RNG k-ε model, the realizable k-ε model, the standard k-ε model, as well as the SST k-ω model. Results were obtained for a blowing ratio of 2.0, and a coolant-to-mainflow temperature ratio of 0.54. The simulations used a dense, high quality, O-type, hexahedral grid. The computed flow/temperature fields are presented, in addition to local, two-dimensional distribution of film cooling effectiveness for the adiabatic and conjugate cases. Results are compared to experimental data in terms of centerline film cooling effectiveness downstream cooling-hole, the predictions with realizable k-ε turbulence model exhibited the best agreement especially in the region for (x/D ≤ 6). All turbulence models predicted the jet lift-off. Also, the results show the effect of the conjugate heat transfer on the temperature (effectiveness) field in the film-cooling hole region and, thus, the additional heating up of the cooling jet itself.

Effects of Film Hole Exit Radiusing on Film Cooling Performance

2016 ◽  
Author(s):  
Antar M. M. Abdala ◽  
Fifi N. M. Elwekeel ◽  
Qun Zheng
Keyword(s):  
Heat Transfer ◽  
Film Cooling ◽  
Discharge Coefficient ◽  
Flux Ratio ◽  
Cooling Effectiveness ◽  
Flow Rates ◽  
Cooling Performance ◽  
Film Cooling Effectiveness ◽  
Net Heat Flux ◽  
Mass Flow Rates

In the present study, theoretical investigation of film cooling effectiveness and heat transfer behavior for radiusing of film hole exit was evaluated. Seven rounding radii of R=0.0D, 0.06D, 0.08D, 0.1D, 0.3D, 0.5D and 0.8D were investigated. The film cooling effectiveness, the heat transfer coefficient, net heat flux ratio and discharge coefficient were investigated. Four mass flow rates in the range of 0.00044: 0.0018[kg/s] were used to investigate the effects of coolant velocity on the film cooling performance. Results show that using the film hole exit radiusing helps in improvement the film cooling effectiveness. The radius of R=0.5D shows higher film cooling effectiveness among the other radii. The spatially average laterally film cooling effectiveness and net heat flux ratio of R=0.5D outperforms the case of R=0.0D at all mass flow rates except at higher rates the values are lower. Discharge coefficient of R=0.5D shows enhancement than R=0.0D with the pressure ratios. Interpretation of the low and high heat transfer coefficient regions for radii of R=0.5D and R= 0.0D depending on the flow structures was explained in detail.

Film Cooling Study of Novel Orthogonal Entrance and Shaped Exit Holes

2009 ◽  
Author(s):  
Santosh Abraham ◽  
Alexander Ritchie Navin ◽  
Srinath V. Ekkad
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Film Cooling ◽  
Geometrical Parameters ◽  
Cooling Effectiveness ◽  
Film Cooling Effectiveness ◽  
Cooling Hole ◽  
Cooling Effects ◽  
Internal Side

Film cooling effectiveness depends on several geometrical parameters like location on the airfoil, exit shape, orientation and arrangement of the holes. The focus of this investigation is to propose and explore a new film cooling hole geometry. The adiabatic film cooling effectiveness is determined experimentally, downstream of the exit of the film cooling holes on a flat plate using a steady state IR thermography technique. Coolant holes that are perpendicular to the direction of flow detach from the surface and enhance the heat transfer coefficient on the turbine blade without providing any coolant coverage, while angled holes along the mainstream direction result in superior film cooling effectiveness and lower heat transfer to the surface. The objective of this study is to examine the external cooling effects using coolant holes that are a combination of both angled shaped holes as well as perpendicular holes. The inlet of the coolant hole is kept perpendicular to the direction of flow to enhance the internal side heat transfer coefficient and the exit of the coolant hole is expanded and angled along the mainstream flow to prevent the coolant jet from lifting off from the blade external surface. A total of six different cases with variations in exit shape geometry are investigated at different blowing ratios (BR varying from 0.5 to 2.0). Results suggest that the film cooling effectiveness values obtained from these geometries are comparable with those of conventional angled holes. With the added advantage of enhanced heat transfer coefficient on the coolant channel internal side, as proven earlier by Byerley [3], overall superior cooling is accomplished. Furthermore this shaped hole can be made using the same technology being presently used in the industry.

Full-Coverage Film Cooling: Heat Transfer Coefficients and Film Effectiveness for a Sparse Hole Array at Different Blowing Ratios and Contraction Ratios

2013 ◽  
Author(s):  
Phillip Ligrani ◽  
Matt Goodro ◽  
Michael D. Fox ◽  
Hee-Koo Moon
Keyword(s):  
Heat Transfer ◽  
Test Section ◽  
Film Cooling ◽  
Hole Array ◽  
Film Cooling Effectiveness ◽  
Blowing Ratio ◽  
Full Coverage ◽  
Contraction Ratio ◽  
Cooling Hole ◽  
Effectiveness Data

The present experimental investigation considers a full coverage film cooling arrangement with differrent streamwise static pressure gradients. The film cooling holes in adjacent streamwise rows are staggered with respect to each other, with sharp edges, and streamwise inclination angles of 20 degrees with respect to the liner surface. Data are provided for turbulent film cooling, contraction ratios of 1 and 4, blowing ratios (at the test section entrance) of 2.0, 5.0, and 10.0, coolant Reynolds numbers of 12,000, freestream temperatures from 75°C to 115°C, a film hole diameter of 7 mm, and density ratios from 1.15 to 1.25. Non-dimensional streamwise and spanwise film cooling hole spacings, X/D and Y/D, are 18, and 5, respectively. Data illustrating the effects of contraction ratio, blowing ratio, and streamwise location on local, line-averaged and spatially-averaged adiabatic film effectiveness data, and on local, line-averaged and spatially-averaged heat transfer coefficient data are presented. Varying blowing ratio values are utilized along the length of the contraction passage, which contains the cooling hole arrangement, when contraction ratio is 4. Dependence on blowing ratio indicates important influences of coolant concentration and distribution. For example, line-averaged and spatially-averaged adiabatic effectiveness data show vastly different changes with blowing ratio BR for the configurations with contraction ratios of 1 and 4. These changes from acceleration are thus mostly due to different blowing ratio distributions along the test section. In particular, much larger effectiveness alterations are present as BR changes from 2.0 to 10.0, when significant acceleration is present and Cr = 4 (in comparison with the Cr = 1 data). When BR = 10.0, much smaller changes due to different contract ratios are present. This is because coolant distributions along the test surfaces are so abundant that magnitudes of streamwise acceleration (and different streamwise variations of blowing ratio) have little effect on near-wall film concentration distributions, or on variations of film cooling effectiveness.

Film Cooling Effectiveness From a Single Scaled-Up Fan-Shaped Hole: A CFD Simulation of Adiabatic and Conjugate Heat Transfer Models

2005 ◽  
Author(s):  
Mahmood Silieti ◽  
Alain J. Kassab ◽  
Eduardo Divo
Keyword(s):  
Heat Transfer ◽  
Turbulence Model ◽  
Film Cooling ◽  
Conjugate Heat Transfer ◽  
Cfd Simulation ◽  
Temperature Fields ◽  
Cooling Effectiveness ◽  
Film Cooling Effectiveness ◽  
Cooling Hole ◽  
Transfer Models

This paper documents a computational investigation of the film cooling effectiveness of a 3-D gas turbine endwall with one fan-shaped cooling hole. The simulations were performed for adiabatic and conjugate heat transfer models. Turbulence closure was investigated using three different turbulence models; the realizable k-ε model, the SST k-ω model, as well as the v2–f turbulence model. Results were obtained for a blowing ratio of one, and a coolant-to-mainflow temperature ratio of 0.54. The simulations used a dense, high quality, O-type, hexahedral grid with three different schemes of meshing for the cooling hole: hexahedral-, hybrid-, and tetrahedral-topology grid. The computed flow/temperature fields are presented, in addition to local, two-dimensional distribution of film cooling effectiveness for the adiabatic and conjugate cases. Results are compared to experimental data in terms of centerline film cooling effectiveness downstream cooling-hole, the predictions with realizable k-ε turbulence model exhibited the best agreement especially in the region for (2 ≤ x/D ≤ 6). Also, the results show the effect of the conjugate heat transfer on the temperature (effectiveness) field in the film cooling hole region and, thus, the additional heating up of the cooling jet itself.

Increasing Adiabatic Film-Cooling Effectiveness by Using an Upstream Ramp

2006 ◽  
Author(s):  
S. Na ◽  
T. I.-P. Shih
Keyword(s):  
Heat Transfer ◽  
Film Cooling ◽  
Stokes Equations ◽  
Surface Heat ◽  
Navier Stokes ◽  
Backward Facing Step ◽  
Film Cooling Effectiveness ◽  
Surface Heat Transfer ◽  
Cooling Hole ◽  
Adiabatic Effectiveness

A new design concept is presented to increase the adiabatic effectiveness of film cooling jets without unduly increasing surface heat transfer and pressure loss. Instead of shaping the film-cooling hole at its downstream end as is done for shaped holes, this study proposes a geometry modification upstream of the film-cooling hole to modify the approaching boundary-layer flow and its interaction with the film-cooling jet. Computations, based on the ensemble-averaged Navier-Stokes equations closed by the realizable k-ε turbulence model, were used to examine the usefulness of making the surface just upstream of the film-cooling hole into a ramp with backward-facing step. The effects of the following parameters were investigated: angle of the ramp (8.5°, 10°, 14°), distance between the backward-facing step of the ramp and the film-cooling hole (0.5D, D), and blowing ratio (0.36, 0.49, 0.56, 0.98). Results obtained show that an upstream ramp with a backward-facing step can greatly increase film-cooling adiabatic effectiveness. The laterally averaged adiabatic effectiveness with ramp can be two or more times higher than without the ramp. Also, the ramp increases the surface area that each film-cooling jet protects. However, using the ramp does increase drag. The increase in surface heat transfer was found to be minimal.

Effect of Film Cooling Hole Area Ratio on Adiabatic Film Cooling Effectiveness Over a Flat Plate

2013 ◽  
Author(s):  
J. Felix ◽  
J. Jim Alen ◽  
Y. Giridhara Babu ◽  
P. Siva Kumar ◽  
N. Vinod Kumar
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Flat Plate ◽  
Film Cooling ◽  
Area Ratio ◽  
Cross Sectional ◽  
Cooling Effectiveness ◽  
Film Cooling Effectiveness ◽  
Hole Area

In the present study the film cooling performance is analyzed for a flat plate model with different hole area ratios. Here “Area Ratio” is defined as the ratio between the cross sectional area of the hole at inlet to the exit of the hole. The area ratios which are considered for analyzing are 1, 2 and 3. The models are made in a 10 mm thickness flat plate with a row of 7 holes having 5 mm diameter and at an angle of 22° towards the downstream. The first model has an area ratio of 1 with a constant cross sectional area throughout the hole. For the second and third models, the area of hole exit is diverged to the corresponding area ratios of 2 and 3 from the mid of the plate. The divergence of hole is made with the area extended towards the downstream. A stainless steel sheet with a low thermal conductivity substrate is placed at the downstream of test model. To study the film cooling performance, two parameters have been considered namely, convective heat transfer coefficient and adiabatic film cooling effectiveness. Both the film effectiveness and convective heat transfer coefficients can be obtained from the same test plate setup. The heat transfer coefficient is obtained by constant heat flux boundary condition over the stainless steel sheet by heating it through current supply. For the film cooling effectiveness measurement, the mainstream is kept at atmospheric temperature and the coolant is maintained at a temperature to attain a constant density ratio equal to 1.3. Experiments are carried out at various blowing ratios in the range of 0.5 to 2. The temperature measurement over the flat plate is measured through an IR camera. Among the considered three models, the model with the higher area ratio had shown higher adiabatic film cooling effectiveness. On analyzing the heat transfer coefficient distribution, no significant changes were found for all the models.

The Effects of Biot Number on the Conjugate Film Cooling Effectiveness Under Different Blowing Ratios

2013 ◽  
Author(s):  
Chao Zhang ◽  
Jian-Jun Liu ◽  
Zhan Wang ◽  
Bai-Tao An
Keyword(s):  
Heat Transfer ◽  
Biot Number ◽  
Film Cooling ◽  
Heat Transfer Analysis ◽  
Upstream Region ◽  
Transfer Resistance ◽  
Cooling Effectiveness ◽  
Film Cooling Effectiveness ◽  
Blowing Ratio ◽  
Cooling Hole

Based on the one-dimensional heat transfer analysis of film cooled turbine blade, the correlation between overall cooling effectiveness and Biot number was obtained, where Biot number represents the ratio of the solid thermal resistance to the external convective heat transfer resistance. And a new parameter — net film cooling effectiveness was defined to evaluate the film cooling performance in the case of conjugate film cooling. Conjugate heat transfer simulation was carried out by using the commercial CFD package CFX for the typical cylindrical film cooling holes on flat plate. The influences of Biot number under different blowing ratios on laterally-averaged overall film cooling effectiveness, laterally-averaged and area-averaged net film cooling effectiveness were investigated systematically. The results showed that due to the effect of solid heat conduction, laterally averaged overall film cooling effectiveness is higher than adiabatic film cooling effectiveness, and the upstream region of the cooling hole can also be cooled by the coolant. With the decrease of Biot number, both the stream-wise and laterally overall cooling effectiveness are more uniform, and laterally-averaged net film cooling effectiveness is reduced. The trend of laterally-averaged net cooling effectiveness under different blowing ratios is consistent with the adiabatic case, but has lower values. For the engine-like Biot number Bi = 0.36, compared with the low blowing ratio M = 0.5 case, the value of area-averaged net film cooling effectiveness is reduced about 29% and 65% correspondingly under blowing ratio M = 1.0 and M = 1.5.

Film Cooling Measurements for a Laidback Fan-Shaped Hole: Effect of Coolant Crossflow on Cooling Effectiveness and Heat Transfer

2018 ◽  
Author(s):  
Marc Fraas ◽  
Tobias Glasenapp ◽  
Achmed Schulz ◽  
Hans-Jörg Bauer
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Film Cooling ◽  
Gas Flow ◽  
Density Ratio ◽  
Coolant Flow ◽  
Cooling Effectiveness ◽  
Film Cooling Effectiveness ◽  
Cooling Hole ◽  
Film Cooling Holes

Internal coolant passages of gas turbine vanes and blades have various orientations relative to the external hot gas flow. As a consequence, the inflow of film cooling holes varies as well. To further identify the influencing parameters of film cooling under varying inflow conditions, the present paper provides detailed experimental data. The generic study is performed in a novel test rig which enables compliance with all relevant similarity parameters including density ratio. Film cooling effectiveness as well as heat transfer of a 10-10-10deg laidback fan-shaped cooling hole are discussed. Data are processed and presented over 50 hole diameters downstream of the cooling hole exit. First, the parallel coolant flow setup is discussed. Subsequently, it is compared to a perpendicular coolant flow setup at a moderate coolant channel Reynolds number. For the perpendicular coolant flow, asymmetric flow separation in the diffuser occurs and leads to a reduction of film cooling effectiveness. For a higher coolant channel Reynolds number and perpendicular coolant flow, asymmetry increases and cooling effectiveness is further decreased. An increase in blowing ratio does not lead to a significant increase in cooling effectiveness. For all cases investigated, heat transfer augmentation due to film cooling is observed. Heat transfer is highest in the near hole region and decreases further downstream. Results prove that coolant flow orientation has a severe impact on both parameters.

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