Multi-Objective Aerodynamic Optimization of Vehicle Shape Using Adjoint Approach Based on Steady-State and Transient Flow Solutions

In order to achieve the purpose of saving energy and reducing emission, the improvement of aerodynamic performance plays an increasingly crucial part for car manufacturers. Previous studies have confirmed the validity of gradient-based adjoint algorithm for its high efficiency and strong robustness in shape optimization, compared with conventional methods. Under these circumstances, this paper aims to explore the application of adjoint approach in vehicle aerodynamic optimization with multiple objectives, transient primal flow solutions, and parameter tuning of turbulence models, which are all issues of high interest in recent practical utilizations. Firstly, multi-objective optimization of reducing both drag and lift was carried out based on a production car. Given the fact that the targets of objective functions are usually conflicting with each other, it’s quite challenging to find the global optimal solution. But with appropriate parameter setting, a reasonable trade-off was achieved that Cd lowered by 8 counts and Cl by 10 counts, which was beneficial for fuel economy as well as driving stability. Secondly, both steady state and transient primal flow simulations were employed and comparatively discussed. After evaluation of the optimized shapes from the two cases, it turned out that the impact of primal solution on design change results could not be neglected, due to the different intrinsic codes of steady-state and transient turbulence models. Finally, as one of the inverse optimization problems, parameter tuning of turbulence models was investigated. Through calibration with wind tunnel test data, the improved parameter combination demonstrates superior performance which could provide more accurate flow solutions, especially aerodynamic forces and characteristic flow patterns. In addition, the current difficulties existed in vehicle aerodynamic optimization were also proposed, serving as a guidance for further researches. Results in this paper suggest that adjoint approach, with a long application history in a variety of disciplines and fields such as aeronautics, geography, turbomachinery, etc., surely will get a more promising and extensive utilization in automotive industry in the near future.