Improved Aerodynamic Prediction Through Coupled System and CFD Models

Abstract

Accurate predictions of aerodynamic forces using computational fluid dynamics require accurate geometry. The aerodynamic forces on the vehicle body affect the vehicle posture or the vehicle position with respect to the ground. When a vehicle is cruising on the road, the change in vehicle posture is usually relatively small with respect to the size of a vehicle. However, these small changes in geometry can lead to significant differences in aerodynamic drag and airflow structures. To address this issue, a coupled simulation approach was developed to predict vehicle posture in typical cruise and wind tunnel test conditions. This coupled approach was tested using Exa's PowerFLOW and Modelon's Vehicle Dynamics Library (VDL). In this approach, the aerodynamic forces on the body are used to calculate the movement of the body and the suspension geometry. This modified geometry is then used to recalculate the operating aerodynamic forces. The modified geometry shows changes in total force, the distribution of forces, and the structure of the airflow over the vehicle. The results provided by correct geometry under loaded conditions offer better correlation to test and provide car makers with the increased accuracy to confidently improve real world fuel economy.