Résumé:
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.
