| The wake survey and the flow field around wheels are really important in the whole external flow field of sedans. Characteristics of wakes have great effects on the aerodynamic drag and lift of sedans. It is noticeable that the flow around the basic body shape is complicated by the presence of the rotating wheels. With regard to the flow around a sedan's wheels, there are too many simplifications in the past studies. Thus, it is necessary to carry out studies about the external flow around a sedan in detail with the rotating wheels condition. At present, it is still difficult to make full-scale sedan experiments in wind tunnels because full-scale rolling roads are rare in the full-scale wind tunnels of the world and surface pressures on rotating wheels are also difficult to obtain. Therefore, we analyzed the wake and flow around the wheels of a homemade sedan in detail with CFD technology in order that we could provide gist and data for wind tunnel experiments.Mesh generation is a critical content in CFD Technology. There are so many kinds of methods of mesh generation that it is important to decide how to select reasonable methods in certain studies. Mesh generation methods were mentioned in most of past research; however, there were not any contrasts among several different methods. Hence, it is significant to make some detailed discussions about the mesh generation technology.Today, the iteration technique dominates most of CFD software. And it is really important to prevent the divergence during the iterating process. Besides turbulence models, discretization schemes and algorithms, the quality of meshes affected the convergence of the computation directly. Toward the actual problems, such as the external flow field around a sedan, it is recommended to apply mature turbulence models, discretization schemes and algorithms. Consequently, the technique of mesh generation is the most uncertain factor in improving the convergence ability and precision of CFD software. This paper illustrated systematically the basics of mesh generation technique, including the methods of generating structured meshes, unstructured meshes, hybrid meshes and their features respectively and mentioned the characteristics of adaptive meshes and cartesian meshes. Recommended methods of selecting mesh strategies were provided for the research of external flow field around sedans. To a certain homemade sedan, five mesh strategies were compared and the general steps of creating meshes were put forward. Then, the mature turbulence model of k-εHigh Reynolds Number and SIMPLE Solution Algorithms were applied to compute the whole external flow field of the sedan using three mesh strategies. The computational results were also compared.The wake survey and the flow field around wheels are emphasized in this paper. The computation results are compared using stationary and rotating wheels condition. Characteristics of flow fields behind wheels were compared between the front wheel and the rear one. Computational results of CD and CL were compared with wind tunnel experiments. The significance of the flow field around wheels was discussed in the automobile design area in order that data for further research of the external flow field around a sedan could be accumulated.CFD is playing an important role not only in the concept car stage, but also in the aerodynamic improvement of vehicles that had been produced. We attempted to ameliorate the aerodynamic performance of this homemade sedan and illustrated the plan of adding a cover on the rear wheel arch. Feasibilities of this plan were discussed. Characteristics of the flow field around the rear wheel and the wake were compared with the counterparts of the prototype. Then, the fuel savings of the plan were estimated roughly.Main conclusions included:1. With regard to research about aerodynamic characteristics of this homemade sedan, the hybrid meshes strategy of tetrahedral cells, prismatic cells and hexahedral cells is effective and efficient.2. Strategies tha... |
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