Application of Function Based Design Method to Automobile Aerodynamic Shape Optimization

Aerodynamic shape optimization with a discrete design variable about an external shape is requested a lot of time-consuming and labor-intensive procedures because of a number of design variables. For this reason, in this study, function based design method is proposed to optimize the external shape of an automobile. It uses the mathematical function for the representation of an automobile. We named the mathematical function to Vehicle Modeling Function(VMF). In case of the shape defined by the VMF, the external configuration can be simply modified just by changing the variables of the function. Therefore, the design variables can be reduced to optimize the shape. Also, it has another advantage in making the scale model for windtunnel test or the computational grid for a numerical analysis. The objective of this paper is to demonstrate the usefulness of the VMF. For the purpose of that, we had conducted the windtunnel test with the scaled model represented by the VMF. In addition, a numerical analysis is performed with the grid generated through the VMF. And then, the VMF is applied to optimize the 3D shape of an automobile actually. After defining the base model using the VMF, 3 variables related to the rear-part of the automobile are applied to the design variables. Through the shape optimization for the low drag and crosswind stability, the optimized shape is efficiently obtained and directly remodeled. From these applications, it is found that the VMF can reduce the design variable and modify the shape easily. Also it is possible to make the scale model and the grid exactly and rapidly. As a result, the VMF is very useful to optimize the 3D aerodynamic shape of an automobile.