Simulation numérique de l'écoulement d'un fluide compressible autour d'un système d'obstacles décalés avec la méthode LES

Abstract

The thesis deals with the study of the flow past a single bluff body in the first part and an array of staggered obstacles in the second part with the use of numerical approaches. Firstly, we have conducted a dynamic and thermal study of the flow past a single obstacle to well understand the flow mechanisms and structures. The main objective is to explore and discuss the effects of rounding the top corners of electronic components which are subjected to a cross-flow and a perpendicular impinging jet on the cooling efficiency. Simulations were performed at a Reynolds number of 3410 for the channel flow and three different impinging-to-cross-flow Reynolds number ratios ( = 0.5, 1 and 1.5 ) based on the radius of the rounded top corner, four cubic geometries were examined. The impacts of the rounded corner on coherent structures and cooling improvement is the principal aim of the study. The Shear Stress Transport (SST) K-ω model is implemented. Moreover, the assessment of this simulation is investigated by comparison with available experimental data. It should be noted that the high mesh resolution was handled where the wall-normal coordinate value is relevant for walls (herein 0.01 y 0.19 +   for the cube wall). Excellent agreement was obtained between the numerical results and experimental data. The coherent structures and flow features created closer to the components significantly influence the wall heat transfer. Furthermore, for  =1 and 1.5 , the cooling effectiveness can be enhanced by more than 6% and 23% respectively with rounding top corners of the cube compared to the base case. In the second part, A large-eddy simulation (LES) study has been undertaken to investigate the turbulent dynamic structure of a fluid flow past two different staggered tube bundles. The first bundle is composed of all circular cylinders and the second is composed of circular and square cylinders. Computations have been conducted for 12,858 D Re = , which match available experiments. To select the appropriate grid, our findings were compared with available experimental data and the GCI method is used to assess the grid refinement influence on the solution. It should be stressed that the mesh density was chosen so that the wall-normal coordinate y+ value is suitable (herein 0.14 y 0.87 +   for the walls cylinders). It turned out that, for the fine mesh, the results get by the considered model corroborate available experimental data and were more accurate than those of Patel obtained with the RANS-SST model. Streamlines, turbulence kinetic energy contours, instantaneous vorticity contours computed indicate that wake patterns are more chaotic in the mixed configuration exhibiting larger recirculation zones compared to the purely circular tube bundle. In addition, flow coherent eddies within both configurations are identified via the Q -criterion. Based on the obtained II findings we can conclude that, in addition to being physically sound, the adopted model is found to be suitable for simulating the turbulent flow over circular and mixed staggered tube bundles with higher resolution.