Large Eddy Simulation of Discrete-Hole Film Cooling in a Flat Plate Turbulent Boundary Layer (original) (raw)
Related papers
2012
A Large Eddy Simulation (LES) is performed of a high blowing ratio (M = 1.7) film cooling flow with density ratio of unity. Mean results are compared with experimental data to show the degree of fidelity achieved in the simulation. While the trends in the LES prediction are a noticeable improvement over Reynolds-Averaged Navier-Stokes (RANS) predictions, there is still a lack a spreading on the underside of the lifted jet. This is likely due to the inability of the LES to capture the full range of influential eddies on the underside of the jet due to their smaller structure. The unsteady structures in the turbulent coolant jet are also explored and related to turbulent mixing characteristics.
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.
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.
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].
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.
Numerical Simulation of Film Cooling Over Flat Plate
New Approaches in Engineering Research Vol. 12, 2021
The effect of film cooling over flat plate is investigated using the commercial CD code; Fluent 6.3. The computational domain includes the coolant supply tube as well as the main mixing region. A tube L/D of 4 and injection angles of (30 o , 60 o , and 90 o) were employed for blowing ratio of (0.33, 0.5, and 1.67), and a density ratio of 1.14. Adiabatic film cooling effectiveness distributions were also determined for inline and staggered arrangements. The main observation from this study that the 30 o hole gave larger effectiveness values than 60 o and 90 o at the blowing ratio of 0.33 with the same length-to-diameter ratio. The maximum effectiveness was achieved with a blowing ratio of 0.5. The results show that the increase of blowing ratio negatively affects film cooling, such that for the blowing ratio of 1.67 the injected coolant tends to lift off from the wall due to the increase of the wall normal momentum. The comparisons for numerical results with experimental data are presented.
Numerical approach to film cooling effectiveness over a plate surface with coolant impingement
Journal of Thermal Science, 2004
ABSTRACT The aim of the present study is conducting the numerical approach to a combination of internal jet impingement and external film cooling over a flat plate. A multi-block three-dimensional Navier-Stokes code, CFX 4.4, with k-ε turbulence model is used to simulate this complicated thermal-flow structure induced by the interaction of coolant jet and hot cross mainstream. By assuming the adiabatic wall boundary condition on the tested film-cooled plate, both the local and the spanwise-averaged adiabatic film cooling effectiveness are evaluated for comparison of the cooling performance at blowing ratios of B r =0.5, 1.0, and 1.5. Film flow data were obtained from a row of five cylindrical film cooling holes, inclined in angle of 35° and 0° in direction of streamwise and spanwise, respectively. The film cooling hole spacing between adjacent holes is 15 mm for all the holes. Before the coolant flow being injected through individual cooling hole then encountered with the mainstream, an impingement chamber containing an impingement plate with 43 holes is located on the path of coolant flow. Present study also focused on the effect of impingement spacing, 10mm, 20mm, and 30mm. Compare the results, we find the impingement jet has a significant effect on the adiabatic film cooling effectiveness. As the coolant impingement spacing is fixed, results indicated that higher blowing ratio would enhance the local and the spanwise-averaged adiabatic film cooling effectiveness. Moreover, neither uniform nor parabolic distribution of pressure distribution are observed within the coolant hole-pipe.
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.
Numerical Study of Film Cooling For Various Coolant Inlet Geometries
The paper deals with the computational investigation of film cooling effectiveness and heat transfer on a 3D flat plate with a cylindrical, elliptic and triangular holes having an inclination of 30 0. Main flow temperature is kept constant at 600K and that of coolant at 300K for all the cases. Centerline and spatially averaged effectiveness are presented for film cooling measurements along non-dimensional temperature profiles in each case. The results for cylindrical case are compared with experimental results and are well in agreement with the experimental results. Comparative studies conducted for the adiabatic film cooling effectiveness and heat transfer coefficient with the three geometries tested (cylindrical, elliptical and triangular hole) reveals that the triangular hole shows much higher effectiveness values than cylindrical case in the near hole region. Also it is observed that triangular hole shows lesser coolant jet height and higher film cooling effectiveness in the region x/D>10, especially at blowing ratios greater than 1.0.
Volume 5B: Heat Transfer, 2015
Full coverage shaped-hole film cooling and downstream heat transfer measurements have been acquired in the accelerating flows over a large cylindrical leading edge test surface. The shaped holes had an 8 deg lateral expansion angled at 30 deg to the surface with spanwise and streamwise spacings of 3 diameters. Measurements were conducted at four blowing ratios, two Reynolds numbers, and six well documented turbulence conditions. Film cooling measurements were acquired over a four to one range in blowing ratio at the lower Reynolds number and at the two lower blowing ratios for the higher Reynolds number. The film cooling measurements were acquired at a coolant to freestream density ratio of approximately 1.04. The flows were subjected to a low turbulence (LT) condition (Tu ¼ 0.7%), two levels of turbulence for a smaller sized grid (Tu ¼ 3.5% and 7.9%), one turbulence level for a larger grid (8.1%), and two levels of turbulence generated using a mock aerocombustor (AC) (Tu ¼ 9.3% and 13.7%). Turbulence level is shown to have a significant influence in mixing away film cooling coverage progressively as the flow develops in the streamwise direction. Effectiveness levels for the AC turbulence condition are reduced to as low as 20% of LT values by the furthest downstream region. The film cooling discharge is located close to the leading edge with very thin and accelerating upstream boundary layers. Film cooling data at the lower Reynolds number show that transitional flows have significantly improved effectiveness levels compared with turbulent flows. Downstream effectiveness levels are very similar to slot film cooling data taken at the same coolant flow rates over the same cylindrical test surface. However, slots perform significantly better in the near discharge region. These data are expected to be very useful in grounding computational predictions of full coverage shaped-hole film cooling with elevated turbulence levels and acceleration. Infrared (IR) measurements were performed for the two lowest turbulence levels to document the spanwise variation in film cooling effectiveness and heat transfer.