Study On The Effects Of Body Rear Structure To Wake Field And The Body Rear Structure Optimization By Computational Fluid Dynamics

As the speed of modern vehicle increasingly high, the effects of aerodynamic characteristics to traction ability, fuel cost, handling and stability have been greater. So, studies on vehicle external flow field and aerodynamic shape have become one of hotspot issues for automobile manufacturing enterprises. The tail flow field is the most complex part of vehicle external flow field. The structure of it lies on vehicle tail modeling. When the tail modeling is changed, it even makes significant impact on the whole external flow field. Therefore, it is one important direction of vehicle aerodynamic study to research the influence of body rear structure to tail flow field and optimize body rear structure. This can give a great theoretical direction and have practical guiding significance to the early design and development of a body.Aiming at the influence of car rear structure to tail flow field, numerical analysis is used to study the tail flow field of cars with different rear structures basing the step back MIRA model. Then, the optimization to the whole rear structure is researched under the front structure of step back MIRA model keeping unchanged. The specific contents are as follow.1.Study on automotive aerodynamics simulation theory and simulation program verification. In order to simulate the tail flow field, the theory of numerical simulation of vehicle aerodynamic is studied. The simulation program is drafted by analyzing the advantages and disadvantages of various turbulence models, the near-wall treatment methods, numerical methods, etc.. Then, the step back MIRA model is established. Mesh and simulation are carried on by CFD software Star-ccm+. The simulation data is compared to that of vehicle wind tunnel test about MIRA model. It can be showed that this simulation program and processing method have high credibility.2.Study on the influence of car rear structure to tail flow field. The different rear structure models based on step back MIRA model are built by analyzing the variation range of side window, roof, rear window, rear end face, rear upswept angle and different length of trunk which consist of the vehicle tail. Then, simulations are done to these models. The influence on the air separation and trailing vortex by changing the different rear body structures is analyzed. Contrasting to aerodynamic drag coefficients of each model, the optimal value of each rear structure parameter can be concluded, which can make the drag coefficients minimal.3.Analyze the optimization of whole rear structure. Keeping the front structure of step back MIRA model unchanged, basing on the optimal value of each rear structure parameter, and considering the interaction of each rear structure, with the goal of minimizing aerodynamic drag coefficient, the Orthogonal experimental design is used to optimize the overall structure of the rear. The importance of each rear structure to the aerodynamic drag coefficient is obtained and the optimum point of each rear structure is concluded. Then, the optimization model of the whole rear structure is built to simulate its external flow field. Contrasting to simulation results of customary step MIRA model, it shows that the whole rear structure optimization makes the aerodynamic drag coefficient reduce 0.04481 and drag reduction rate arrives at 14.31%. This can greatly reduce vehicle air resistance and improve vehicle economy.