基于自由变形技术的Ahmed模型气动减阻优化

针对目前汽车气动减阻中基于工程师经验的试凑法所存在的盲目性和低效率，以及气动优化设计中车身曲面难于参数化等问题，将自由变形方法引入汽车气动减阻优化设计中，为减阻优化设计提供一种快速、有效的参数化方法.文中以外形简单的Ahmed模型为研究对象，根据正交试验设计构建样本空间，采用FFD方法对各样本点模型进行参数化，通过CFD仿真获得各样本的气动阻力系数；建立3种常用的近似模型，选择可信度最高的RBF模型构建近似模型，采用多岛遗传算法求解近似模型的最优值，根据优化结果重新构建最优模型并采用CFD计算其气动阻力系数.计算结果显示优化后的Ahmed模型气动阻力系数减少了51.96%. 

Aerodynamic Drag Reduction of Ahmed Model Based on Free Form Deformation

At present,the most common approach for vehicle aerodynamic drag reduction is trial and error method,which completely depended on the engineers'experience.Inevitably,this method is certain blindness and low efficiency.Moreover,it is quite difficult to parameterize the auto body in the aerodynamic optimization design.To solve these problems,a fast and effective parameterization method named FFD (free form deformation)was introduced into the vehicle aerodynamic optimization design.Firstly,taking the Ahmed model as the simulation obj ect, sample space was constructed based on the orthogonal array experiment design,and FFD method was used to parameterize the model at each sample point.Secondly,the aerodynamic drag coefficient of each sample was confirmed by CFD simulation.Then,according to the sample space and computational results obtained by CFD,three kinds of approximate model were constructed, and the RBF model with highest credibility was selected to build the approximate model.Finally, the multi-island genetic algorithm was employed to get the optimal combination of the design variables.To validate the reliability of the final results,a new model was reconstructed according to the results of the optimization,and aerodynamic drag coefficient was computed by CFD again. The computational results show that the Ahmed model aerodynamic drag coefficient can be decreased by 51.96% after optimization,which confirms that FFD method deserves to be popularized in vehicle aerodynamic optimization design.