Numerical Analysis of Cooling Drag and Front Lift Interaction on a Ford Focus

Abstract

Changes in front lift have been observed by Ford Motor Company and other OEMs (original equipment manufacturers) when varying the amount of cooling ow. This ow phenomena is not yet fully understood, further the predictions made by CFD (Computational Fluid Dynamics) have shown to underpredict front lift compared to experiments. The thesis work aims to increase understanding of how cooling ow e ects front lift as well as investigate the accuracy of unsteady FVM (Finite Volume Method) CFD simulations. The FVM simulation results are compared to wind tunnel tests and results from another solver using the LBM (Lattice Boltzmann Method) with focus on cooling ow and predicted trends between vehicle con gurations. Drag is of larger interest than lift when optimizing road vehicle aerodynamics, however, front lift and the overall lift balance of a vehicle e ects high speed handling with e ects apparent at speeds over 80 km/h. The results show that front lift is increased due to cooling ow and that the largest changes in cooling drag and front lift are located at the front part of the car. The front lift increase due to cooling ow is due to two components; the lift component and the drag component which changes the front and rear lift distribution. The accuracy and trend-predicting capability of the FVM and LBM simulations is similar for the numerical setup used in this thesis. The numerical solvers were often closer to each other than to experimental values.