A Detailed Analysis of Film-Cooling Physics: Part I—Streamwise Injection With Cylindrical Holes

1997 ◽  
Vol 122 (1) ◽  
pp. 102-112 ◽  
Author(s):  
D. K. Walters ◽  
J. H. Leylek
Keyword(s):  
Experimental Data ◽  
Turbulence Model ◽  
Film Cooling ◽  
Stokes Equations ◽  
Density Ratio ◽  
Three Dimensional ◽  
Layer Model ◽  
Flow Physics ◽  
Advantages And Disadvantages ◽  
Two Layer Model

A previously documented systematic computational methodology is implemented and applied to a jet-in-crossflow problem in order to document all of the pertinent flow physics associated with a film-cooling flowfield. Numerical results are compared to experimental data for the case of a row of three-dimensional, inclined jets with length-to-diameter ratios similar to a realistic film-cooling application. A novel vorticity-based approach is included in the analysis of the flow physics. Particular attention has been paid to the downstream coolant structures and to the source and influence of counterrotating vortices in the crossflow region. It is shown that the vorticity in the boundary layers within the film hole is primarily responsible for this secondary motion. Important aspects of the study include: (1) a systematic treatment of the key numerical issues, including accurate computational modeling of the physical problem, exact geometry and high-quality grid generation techniques, higher-order numerical discretization, and accurate evaluation of turbulence model performance; (2) vorticity-based analysis and documentation of the physical mechanisms of jet–crossflow interaction and their influence on film-cooling performance; (3) a comparison of computational results to experimental data; and (4) comparison of results using a two-layer model near-wall treatment versus generalized wall functions. Solution of the steady, time-averaged Navier–Stokes equations were obtained for all cases using an unstructured/adaptive grid, fully explicit, time-marching code with multigrid, local time stepping, and residual smoothing acceleration techniques. For the case using the two-layer model, the solution was obtained with an implicit, pressure-correction solver with multigrid. The three-dimensional test case was examined for two different film-hole length-to-diameter ratios of 1.75 and 3.5, and three different blowing ratios, from 0.5 to 2.0. All of the simulations had a density ratio of 2.0, and an injection angle of 35 deg. An improved understanding of the flow physics has provided insight into future advances to film-cooling configuration design. In addition, the advantages and disadvantages of the two-layer turbulence model are highlighted for this class of problems. [S0889-504X(00)01201-0]

scholarly journals A Detailed Analysis of Film–Cooling Physics: Part I — Streamwise Injection With Cylindrical Holes

1997 ◽  
Author(s):  
Dibbon K. Walters ◽  
James H. Leylek
Keyword(s):  
Experimental Data ◽  
Turbulence Model ◽  
Film Cooling ◽  
Stokes Equations ◽  
Density Ratio ◽  
Three Dimensional ◽  
Layer Model ◽  
Flow Physics ◽  
Advantages And Disadvantages ◽  
Two Layer Model

A previously documented systematic computational methodology is implemented and applied to a jet–in–crossflow problem in order to document all of the pertinent flow physics associated with a film–cooling flowfield. Numerical results are compared to experimental data for the case of a row of three–dimensional, inclined jets with length–to–diameter ratios similar to a realistic film–cooling application. A novel vorticity based approach is included in the analysis of the flow physics. Particular attention has been paid to the downstream coolant structures and to the source and influence of counter–rotating vortices in the crossflow region. It is shown that the vorticity in the boundary layers within the film hole is primarily responsible for this secondary motion. Important aspects of the study include: (1) a systematic treatment of the key numerical issues, including accurate computational modeling of the physical problem, exact geometry and high quality grid generation techniques, higher–order numerical discretization, and accurate evaluation of turbulence model performance; (2) vorticity–based analysis and documentation of the physical mechanisms of jet–crossflow interaction and their influence on film–cooling performance; (3) a comparison of computational results to experimental data; and (4) comparison of results using a two–layer model near–wall treatment versus generalized wall functions. Solution of the steady, time–averaged Navier–Stokes equations were obtained for all cases using an unstructured/adaptive grid, fully explicit, time–marching code with multi–grid, local time stepping, and residual smoothing acceleration techniques. For the case using the two–layer model, the solution was obtained with an implicit, pressure–correction solver with multi–grid. The three–dimensional test case was examined for two different film–hole length–to–diameter ratios of 1.75 and 3.5, and three different blowing ratios, from 0.5 to 2.0. All of the simulations had a density ratio of 2.0, and an injection angle of 35°. An improved understanding of the flow physics has provided insight into future advances to film–cooling configuration design. In addition, the advantages and disadvantages of the two–layer turbulence model are highlighted for this class of problems.

scholarly journals Three-Dimensional Turbulent Vortex Shedding From a Surface-Mounted Square Cylinder: Predictions With Large-Eddy Simulations and URANS

2014 ◽  
Vol 136 (6) ◽  
Author(s):  
B. A. Younis ◽  
A. Abrishamchi
Keyword(s):  
Experimental Data ◽  
Turbulence Model ◽  
Stokes Equations ◽  
Three Dimensional ◽  
Large Eddy Simulations ◽  
Navier Stokes ◽  
Reynolds Stresses ◽  
Mean Flow ◽  
Navier Stokes Equations ◽  
Large Eddy

The paper reports on the prediction of the turbulent flow field around a three-dimensional, surface mounted, square-sectioned cylinder at Reynolds numbers in the range 104–105. The effects of turbulence are accounted for in two different ways: by performing large-eddy simulations (LES) with a Smagorinsky model for the subgrid-scale motions and by solving the unsteady form of the Reynolds-averaged Navier–Stokes equations (URANS) together with a turbulence model to determine the resulting Reynolds stresses. The turbulence model used is a two-equation, eddy-viscosity closure that incorporates a term designed to account for the interactions between the organized mean-flow periodicity and the random turbulent motions. Comparisons with experimental data show that the two approaches yield results that are generally comparable and in good accord with the experimental data. The main conclusion of this work is that the URANS approach, which is considerably less demanding in terms of computer resources than LES, can reliably be used for the prediction of unsteady separated flows provided that the effects of organized mean-flow unsteadiness on the turbulence are properly accounted for in the turbulence model.

Heat Transfer in Film-Cooled Turbine Blades

1993 ◽  
Author(s):  
Vijay K. Garg ◽  
Raymond E. Gaugler
Keyword(s):  
Heat Transfer ◽  
Experimental Data ◽  
Film Cooling ◽  
Stokes Equations ◽  
Turbine Blades ◽  
Three Dimensional ◽  
Navier Stokes ◽  
Navier Stokes Equations ◽  
Explicit Finite Difference ◽  
Control Volumes

In order to study the effect of film cooling on the flow and heat transfer characteristics of actual turbine blades, a three-dimensional Navier-Stokes code has been developed. An existing code (Chima and Yokota, 1990) has been modified for the purpose. The code is an explicit finite difference code with an algebraic turbulence model. The thin-layer Navier-Stokes equations are solved using a general body-fitted coordinate system. The effects of film cooling have been incorporated into the code in the form of appropriate boundary conditions at the hole locations on the blade surface. Each hole exit is represented by several control volumes, thus providing an ability to study the effect of hole shape on the film-cooling characteristics. Comparison with experimental data is fair. Further validation of the code is required, however, and in this respect, there is an urgent need for detailed experimental data on actual turbine blades.

Curvature Effects on Discrete-Hole Film Cooling

1999 ◽  
Vol 121 (4) ◽  
pp. 781-791 ◽  
Author(s):  
M. K. Berhe ◽  
S. V. Patankar
Keyword(s):  
Film Cooling ◽  
Stokes Equations ◽  
Convex Surface ◽  
Numerical Study ◽  
Turbulent Viscosity ◽  
Density Ratio ◽  
Three Dimensional ◽  
Cooling Effectiveness ◽  
Streamline Curvature ◽  
Curvature Effects

A numerical study has been conducted to investigate the effects of surface curvature on cooling effectiveness using three-dimensional film cooling geometries that included the mainflow, injection hole, and supply plenum regions. Three surfaces were considered in this study, namely, convex, concave, and flat surfaces. The fully elliptic, three-dimensional Navier–Stokes equations were solved over a body-fitted grid. The effects of streamline curvature were taken into account by using algebraic relations for the turbulent viscosity and the turbulent Prandtl number in a modified k–ε turbulence model. Computations were performed for blowing ratios of 0.5, 1.0, and 1.5 at a density ratio of 2.0. The computed and experimental cooling effectiveness results were compared. For the most part, the cooling effectiveness was predicted quite well. A comparison of the cooling performances over the three surfaces reveals that the effect of streamline curvature on cooling effectiveness is very significant. For the low blowing ratios considered, the convex surface resulted in a higher cooling effectiveness than both the flat and concave surfaces. The flow structures over the three surfaces also exhibited important differences. On the concave surface, the flow involved a stronger vorticity and greater mixing of the coolant jet with the mainstream gases. On the convex surface, the counterrotating vortices were suppressed and the coolant jet pressed to the surface by a strong cross-stream pressure gradient.

Physics of Hot Crossflow Ingestion in Film Cooling

1999 ◽  
Vol 121 (3) ◽  
pp. 532-541 ◽  
Author(s):  
E. L. McGrath ◽  
J. H. Leylek
Keyword(s):  
Reynolds Number ◽  
Gas Turbine ◽  
Film Cooling ◽  
Stokes Equations ◽  
Density Ratio ◽  
Lessons Learned ◽  
Wall Functions ◽  
Flow Physics ◽  
Blowing Ratio ◽  
Compound Angle

Computational fluid dynamics (CFD) is used to isolate the flow physics responsible for hot crossflow ingestion, a phenomenon that can cause failure of a film cooled gas turbine component. In the gas turbine industry, new compound-angle shaped hole (CASH) geometries are currently being developed to decrease the heat transfer coefficient and increase the adiabatic effectiveness on film cooled surfaces. These new CASH geometries can have unexpected flow patterns that result in hot crossflow ingestion at the film hole. This investigation examines a 15 deg forward-diffused film hole injected streamwise at 35 deg with a compound angle of 60 deg (FDIFF60) and with a length-to-diameter ratio (L/D) of 4.0. Qualitative and quantitative aspects of computed results agreed well with measurements, thus lending credibility to predictions. The FDIFF60 configuration is a good representative of a typical CASH geometry, and produces flow mechanisms that are characteristic of CASH film cooling. FDIFF60 has been shown to have impressive downstream film cooling performance, while simultaneously having undesirable ingestion at the film hole. In addition to identifying the physical mechanisms driving ingestion, this paper documents the effects on ingestion of the blowing ratio, the density ratio, and the film hole Reynolds number over realistic gas turbine ranges of 0.5 to 1.88, 1.6 to 2.0, and 17,350 to 70,000, respectively. The results of this study show that hot crossflow ingestion is caused by a combination of coolant blockage at the film hole exit plane and of crossflow boundary layer vorticity that has been re-oriented streamwise by the presence of jetting coolant. Ingestion results when this re-oriented vorticity passes over the blocked region of the film hole. The density ratio and the film hole Reynolds number do not have a significant effect on ingestion over the ranges studied, but the blowing ratio has a surprising nonlinear effect. Another important result of this study is that the blockage of coolant hampers convection and allows diffusion to transfer heat into the film hole even when ingestion is not present. This produces both an undesirable temperature gradient and high temperature level on the film hole wall itself. Lessons learned about the physics of ingestion are generalized to arbitrary CASH configurations. The systematic computational methodology currently used has been previously documented and has become a standard for ensuring accurate results. The methodology includes exact modeling of flow physics, proper modeling of the geometry including the crossflow, plenum, and film hole regions, a high quality mesh for grid independent results, second order discretization, and the two-equation k–ε turbulence model with generalized wall functions. The steady, Reynolds-averaged Navier–Stokes equations are solved using a fully elliptic and fully implicit pressure-correction solver with multiblock unstructured and adaptive grid capability and with multigrid convergence acceleration.

scholarly journals Curvature Effects on Discrete-Hole Film Cooling

1998 ◽  
Author(s):  
Mulugeta K. Berhe ◽  
Suhas V. Patankar
Keyword(s):  
Film Cooling ◽  
Stokes Equations ◽  
Convex Surface ◽  
Numerical Study ◽  
Turbulent Viscosity ◽  
Density Ratio ◽  
Three Dimensional ◽  
Cooling Effectiveness ◽  
Streamline Curvature ◽  
Curvature Effects

A numerical study has been conducted to investigate the effects of surface curvature on cooling effectiveness using three-dimensional film cooling geometries that included the mainflow, injection hole, and supply plenum regions. Three surfaces were considered in this study, namely, convex, concave, and flat surfaces. The fully elliptic, three-dimensional Navier-Stokes equations were solved over a body-fitted grid. The effects of streamline curvature were taken into account by using algebraic relations for the turbulent viscosity and the turbulent Prandtl number in a modified k-ε turbulence model. Computations were performed for blowing ratios of 0.5, 1.0, and 1.5 at a density ratio of 2.0. The computed and experimental cooling effectiveness results were compared. For the most part, the cooling effectiveness was predicted quite well. A comparison of the cooling performances over the three surfaces reveals that the effect of streamline curvature on cooling effectiveness is very significant. For the low blowing ratios considered, the convex surface resulted in a higher cooling effectiveness than both the flat and concave surfaces. The flow structures over the three surfaces also exhibited important differences. On the concave surface, the flow involved a stronger vorticity and greater mixing of the coolant jet with the mainstream gases. On the convex surface, the counter-rotating vortices were suppressed and the coolant jet pressed to the surface by a strong cross-stream pressure gradient.

scholarly journals Physics of Hot Crossflow Ingestion in Film Cooling

1998 ◽  
Author(s):  
E. Lee McGrath ◽  
James H. Leylek
Keyword(s):  
Reynolds Number ◽  
Gas Turbine ◽  
Film Cooling ◽  
Stokes Equations ◽  
Density Ratio ◽  
Lessons Learned ◽  
Wall Functions ◽  
Flow Physics ◽  
Blowing Ratio ◽  
Compound Angle

Computational fluid dynamics (CFD) is used to isolate the flow physics responsible for hot crossflow ingestion, a phenomenon that can cause failure of a film cooled gas turbine component. In the gas turbine industry, new compound-angle shaped hole (CASH) geometries are currently being developed to decrease the heat transfer coefficient and increase the adiabatic effectiveness on film cooled surfaces. These new CASH geometries can have unexpected flow patterns that result in hot crossflow ingestion at the film hole. This investigation examines a 15° forward-diffused cylindrical film hole injected streamwise at 35° with a compound angle of 60° (FDIFF60) and with a length-to-diameter ratio (L/D) of 4.0. Qualitative and quantitative aspects of computed results agreed well with measurements, thus lending credibility to predictions. The FDIFF60 configuration is a good representative of a typical CASH geometry, and produces flow mechanisms that are characteristic of CASH film cooling. FDIFF60 has been shown to have impressive downstream film cooling performance, while simultaneously having undesirable ingestion at the film hole. In addition to identifying the physical mechanisms driving ingestion, this paper documents the effects on ingestion of the blowing ratio, the density ratio, and the film hole Reynolds number over realistic gas turbine ranges of 0.5 to 1.88, 1.6 to 2.0, and 17,350 to 70,000, respectively. The results of this study show that hot crossflow ingestion is caused by a combination of coolant blockage at the film hole exit plane and of crossflow boundary layer vorticity that has been re-oriented streamwise by the presence of jetting coolant: Ingestion results when this re-oriented vorticity passes over the blocked region of the film hole. The density ratio and the film hole Reynolds number do not have a significant effect on ingestion over the ranges studied, but the blowing ratio has a surprising non-linear effect. Another important result of this study is that the blockage of coolant hampers convection and allows diffusion to transfer heat into the film hole even when ingestion is not present. This produces both an undesirable temperature gradient and high temperature level on the film hole wall itself. Lessons learned about the physics of ingestion are generalized to arbitrary CASH configurations. The systematic computational methodology currently used has been previously documented and has become a standard for ensuring accurate results. The methodology includes exact modeling of flow physics, proper modeling of the geometry including the crossflow, plenum, and film hole regions, a high quality mesh for grid independent results, second order discretization, and the two-equation k-ε turbulence model with generalized wall functions. The steady, Reynolds-averaged Navier-Stokes equations are solved using a fully-elliptical and fully-implicit pressure-correction solver with multi-block unstructured and adaptive grid capability and with multi-grid convergence acceleration.

Numerical Evaluation of Novel Shaped Holes for Enhancing Film Cooling Performance

2015 ◽  
Vol 137 (7) ◽  
Author(s):  
Xing Yang ◽  
Zhao Liu ◽  
Zhenping Feng
Keyword(s):  
Experimental Data ◽  
Turbulence Model ◽  
Film Cooling ◽  
Density Ratio ◽  
Cylindrical Hole ◽  
Transfer Coefficients ◽  
Cooling Performance ◽  
Film Cooling Effectiveness ◽  
Blowing Ratio ◽  
Wide Range

The overall film cooling performance of three novel film cooling holes has been numerically investigated in this paper, including adiabatic film cooling effectiveness, heat transfer coefficients as well as discharge coefficients. The novel holes were proposed to help cooling injection spread laterally on a cooled endwall surface. Three-dimensional Reynolds-averaged Navier–Stokes (RANS) equations with shear stress transport (SST) k-ω turbulence model were solved to perform the simulation based on turbulence model validation by using the relevant experimental data. Additionally, the grid independent test was also carried out. With a mainstream Mach number of 0.3, flow conditions applied in the simulation vary in a wide range of blowing ratio from 0.5 to 2.5. The coolant-to-mainstream density ratio (DR) is fixed at 1.75, which can be more approximate to real typical gas turbine applications. The numerical results for the cylindrical hole are in good agreement with the experimental data. It is found that the flow structures and temperature distributions downstream of the cooling injection are significantly changed by shaping the cooling hole exit. For a low blowing ratio of 0.5, the three novel shaped cooling holes present similar film cooling performances with the traditional cylindrical hole, while with the blowing ratio increasing, all the three novel cooling holes perform better, of which the bean-shaped hole is considered to be the best one in terms of the overall film cooling performance.

scholarly journals Computation of Discrete-Hole Film Cooling: A Hydrodynamic Study

1997 ◽  
Author(s):  
Mulugeta K. Berhe ◽  
Suhas V. Patankar
Keyword(s):  
Film Cooling ◽  
Stokes Equations ◽  
Numerical Study ◽  
Control Volume ◽  
Density Ratio ◽  
Three Dimensional ◽  
Lateral Spread ◽  
Injection Hole ◽  
Mean Velocity ◽  
Resultant Velocity

Hydrodynamic plots are presented from a numerical study conducted on a three dimensional film cooling geometry that includes the main flow, injection hole, and the plenum. The fully elliptic Navier-Stokes equations were solved over a body fitted grid using the control volume method. Turbulence closure was achieved using the k-ε turbulence model. The results presented include contour plots of the resultant velocity at hole exit, as well as streamwise mean velocity and turbulence intensity contours at several cross-stream planes. Computations were performed for blowing ratios of 0.5 and 1.0, and a density ratio of 2. The injection hole was 12.7 mm in diameter, 3.5 diameters long, and inclined at 35° to the streamwise direction. Results obtained from this analysis are compared with the available experimental results. Whereas the overall agreement is good, important differences were found. Compared to the experimental jet, the computed jet showed (a) a larger vertical velocity at hole exit, (b) a smaller lateral spread in the downstream region, especially at low blowing ratios.

Quantitative Flow Imaging of Film Cooling Jets in a Cross-Flow Using Particle Image Velocimetry and Computational Fluid Dynamics

2020 ◽  
Author(s):  
Robin G. Brakmann ◽  
Robin Schöffler ◽  
Frank Kocian ◽  
Michael Schroll ◽  
Christian Willert ◽  
...  
Keyword(s):  
Turbulence Model ◽  
Film Cooling ◽  
Density Ratio ◽  
Three Dimensional ◽  
Cross Flow ◽  
Flux Ratio ◽  
Turbulent Heat Flux ◽  
Turbulent Heat ◽  
Stable Model ◽  
Algebraic Models

Abstract The investigated generic configuration consists of cylindrical film cooling holes with a diameter of D = 8.4 mm and an inclination angle of α = 35°. The jets are characterized by a momentum flux ratio of I = 0.63, a density ratio of DR = 0.94 and a cross-flow Reynolds number of Re = 5500. Stereoscopic PIV allows creating a (pseudo) three dimensional image of the flow field. High resolution PIV is used to evaluate velocity fluctuations. The numerical model uses the SST and an EARSM turbulence model. The turbulent scalar fluxes are computed by a constant turbulent Prandtl number as well as algebraic models for the turbulent heat flux. The presented results consist of field cuts and line profiles of the velocity, vorticity and turbulent kinetic energy. All considered numerical options can predict the velocity field accurately, the SST turbulence model is the numerically most stable model and has the lowest demands in computational costs.

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