Large Eddy Simulation of a Film Cooling Flow Injected From an Inclined Discrete Cylindrical Hole Into a Crossfl ow With Zero-Pressure Gradient Turbulent Boundary Layer (original) (raw)
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Large Eddy Simulation of Discrete-Hole Film Cooling in a Flat Plate Turbulent Boundary Layer
38th AIAA Thermophysics Conference, 2005
Large eddy simulation has been applied to an example discrete hole film cooling configuration. The computational domain included the coolant supply tube as well as the main mixing region. A tube L/D of 8 and an injection angle of 35 degrees was employed for a simulation with a blowing ratio of 0.5 and a density ratio of 2 to demonstrate that realistic cooling conditions can be simulated. Comparisons with experimental data are underway and will be included in the final paper. Nomenclature Re d Reynolds number based on displacement thickness L the length of pipe D the diameter of coolant supply pipe η adiabatic effectiveness δ d displacement thickness δ boundary layer thickness U inf nondimensional free stream mean velocity T U free stream turbulent level DR Density ratio M blowing ratio Subscript w wall property c the coolant property inf free stream property
International Journal of Heat and Fluid Flow, 2008
A numerical investigation is conducted to study leading edge film cooling with large eddy simulation (LES). The domain geometry is adopted from an experimental setup of . Detailed film cooling measurement on a cylindrical leading edge model: Effect of free-stream turbulence and coolant density. Journal of Turbomachinery 120, 799-807.] where turbine blade leading edge is represented by a semi-cylindrical blunt body with compound angle of injection. At blowing ratio of 0.4 and coolant to mainstream density ratio of unity, a laminar constant velocity and fully-turbulent coolant jet are studied. In both cases, the results show the existence of an asymmetric counter-rotating vortex pair in the immediate wake of the coolant jet. In addition to these primary structures, vortex tubes on the windward side of the jet are convected downstream over and to the aft-and fore-side of the counter-rotating vortex pair. All these structures play a role in the mixing of mainstream fluid with the coolant. The fully-turbulent coolant jet increases mixing with the mainstream in the outer shear layer but does not directly influence the flow dynamics in the turbulent boundary layer which forms within two coolant hole diameters of injection. As a result, the turbulent jet decreases adiabatic effectiveness but does not have a substantial effect on the heat transfer coefficient. The span-wise averaged adiabatic effectiveness agrees well with experiments for a turbulent coolant jet, without which the calculated effectiveness is over-predicted. On the other hand, the heat transfer coefficient which is only a function of near wall turbulence, shows good agreement with experiments for both coolant jet inlet conditions.
Detailed investigation of film cooling for a cylindrical leading edge is carried out using large eddy simulation (LES). The paper focuses on the effects of coolant to mainstream blowing ratio on flow features and, consequently, on the adiabatic effectiveness and heat transfer coefficient. With the advantage of obtaining unique, accurate, and dynamic results from LES, the influential coherent structures in the flow are identified. Describing the mechanism of jet-mainstream interaction, it is shown that as the blowing ratio increases, a more turbulent shear layer and stronger mainstream entrainment occur. The combined effects lead to a lower adiabatic effectiveness and higher heat transfer coefficient. Surface distribution and span-averaged profiles are shown for both adiabatic effectiveness and heat transfer (presented by Frossling number). Results are in good agreement with the experimental data of Ekkad et al. [1998, "Detailed Film Cooling Measurement on a Cylindrical Leading Edge Model: Effect of Free-Steam Turbulence and Coolant Density," ASME J. Turbomach., 120, pp. 799-807].
Proceeding of 5th Thermal and Fluids Engineering Conference (TFEC)
The higher temperature of the combustion chamber of a gas turbine yield higher efficiencies for the turbines but can affect the blade's life. As a preventative method, Film-cooling is a useful technique to enhance the performance of it by injecting coolant jets that the metal surfaces can be protected against the hot main flow. To improve cooling efficiency and increase the life of these components, several cooling strategies have been introduced. In the present study, the effects of the laidback fan-shaped hole geometry, in particular, are examined against the conventional cylindrical hole geometry using Computational Fluid Dynamic simulations. Computations are carried out based on three-dimensional Large Eddy Simulation. The open-source software OpenFOAM was utilized to solve the filtered governing equations for mass, momentum, energy conservation, and heat transfer. The mixing mechanism between hot and coolant fluids, nondimensional adiabatic film cooling effectiveness, and dynamics of vortices are presented and discussed.
LES of Turbulent Mixing In Anti-Vortex Film Cooling Flows
The Anti-vortex film cooling technique is investigated by using large eddy simulation (LES) due to its complex mixture between the mainstream flow, the film cooling flow, and the flow through the anti-vortex holes. A geometry of single row of 30 degree round holes on a flat plate is used as the baseline case. Three different values of velocity ratios (Coolant Jet Velocity/Main Stream Velocity) are studied. Two different positions of the anti-vortex holes are investigated with temperature ratio (main stream temperature / coolant temperature) namely 2. The density ratio is taken in consideration. Use of symmetry boundary condition is avoided to capture three dimensional, unsteady, turbulent nature of the flow. Present simulation is carried out by using FLUENT commercial code. Numerical calculation of film cooling effectiveness is validated with reported experimental results. Results show that the used anti-vortex technique improves the film cooling effectiveness. The numerical boundary layer velocity vectors showed that the anti-vortex holes create reverse vortices against the main vortices that are created by the main hole. These reverse vortices help in keeping the coolant jet flow near the surface.
CFD Modeling of Film Cooling Flow with Inclined Jets
Journal of Advances in Applied & Computational Mathematics, 2016
Film cooling has been widely used to control temperature of high temperature and high pressure blades. In a film cooled blade the air taken from last compressor stages is ejected through discrete holes drilled on blade surface to provide a cold layer between hot mainstream and turbine components. A comprehensive understanding of phenomena concerning the complex interaction of hot gasses with coolant flows in a vane passage plays a major role in the definition of a well performing film cooling scheme. In this study turbulent film cooling flow has been studied numerically. The computational simulation is conducted by employing the Reynolds Averaged Navier-Stokes (RANS) approach. The standard k ! " model with enhanced wall treatment has been implemented for modeling the turbulent flow. Effects of different cooling holes temperature have been studied on the surface of the blade and as results show the temperature of the surface reduces significantly as the temperatures of the cooling holes decreases.
Journal of Applied Fluid Mechanics, 2016
Flow hydrodynamic effects and film cooling effectiveness of placing a coolant port (upstream jet) just upstream of the main cooling jet were numerically investigated. The upstream jet was added such that the total cooling cross section (cross sections of the main and upstream jets) remains constant, in comparison to the case of ordinary cooling jet. The finite volume method and the unsteady SIMPLE algorithm on a multiblock non-uniform staggered grid arrangement were applied. The large eddy simulation (LES) approach with the one equation subgrid scale model was used. The jet to cross flow velocity ratio (for both of the main and the upstream jets) is 0.5 and the cross flow Reynolds number (based on the main jet parameters) is equal to 4700. The obtained results showed a significant improvement in the flow control capability and both centerline and span-wise averaged film cooling effectiveness applying the new cooling configuration. Effects of the upstream jet dimensions are also studied here. The obtained results showed that the span-wise width of the upstream jet has more essential influence on the cooling performance than that of its stream-wise width. Moreover, it is demonstrated that the film cooling performance could be enhanced even by applying an upstream jet which its temperature is as same as the cross-flow temperature, i.e. applying a hot upstream jet. Finally, it is shown that presence of the upstream jet decreases the stream-wise component of the velocity near the wall, which decreases the wall shear stress and the skin friction drag coefficient significantly.
The Influence of Discretization Scheme on Large Eddy Simulations of Discrete Film Cooling Holes
46th AIAA/ASME/SAE/ASEE Joint Propulsion Conference & Exhibit, 2010
Large Eddy Simulations were performed on a simple angle cylindrical film cooling hole with a 35° inclination angle and a length-to-diameter ratio of 3.5. A density ratio of 1.25 and velocity ratio of 0.80 was employed, yielding a mass flux ratio of 1.0 and momentum flux ratio of 0.80. Three different discretization schemes were used in otherwise identical simulations: bounded central differencing, pure second-order upwind, and pure secondorder central differencing. The results of these three cases are compared with experimental data from open literature studies in terms of surface adiabatic effectiveness, mean temperature and velocity fields, and unsteady turbulence characteristics. The pure central differencing scheme was found to perform the best in this film cooling scenario, while the upwind scheme also preformed well. The bounded central scheme compared poorly with the experimental data and the other two schemes. The present investigation was made in an attempt to further explore the abilities of Large Eddy Simulations to resolve the complex flow structure arising from the injection of a film cooling jet into a turbine hot gas path.
NUMERICAL SIMULATION FOR FILM COOLING TECHNIQUE WITH INLET BOUNDARY CONDITIONS PERTURBATION
iaeme
Large Eddy Simulation approach of flow field and film cooling effectiveness is performed using the Fluent Computational Fluid Dynamics code and carried out by using the LES turbulence model. This simulation of mean velocity and turbulent kinetic energy fields are presented for lateral jet in crossflow at injection angle of 35°. The blowing ratio is = 0.5 R M . The flow obtained in such a periodic domain is described, focusing on information relevant to estimation of mass/momentum/energy fluxes through the plate. LES results underline the potential of the approach for industrial use. Keywords: Large eddy simulation, Film cooling, interaction jet, turbulent jet.
Film cooling of a two-dimensional flat plate at different jet to cross flow velocity ratios (R) is simulated at the jet Reynolds number of 4700, using large eddy simulation (LES) approach. Our computational methodology includes the use of finite volume method, applying the unsteady SIMPLE algorithm and a multi-block and nonuniform staggered grid. The governing equations have been discretized applying the Power-Law scheme for the spatial terms and the Crank-Nicolson scheme for the temporal terms. Two solution approaches are discussed here, namely:1-neglecting and 2-considering density ratio effects. The results showed that the density ratio has significant effects on the flow structures, namely on the penetration, the expansion, and the reattachment point of the vortical regions. Therefore, it changes the temperature distribution and the film cooling effectiveness, and thus, it should not be easily neglected.