Quantitative analysis of vehicle aerodynamics during crosswind gusts

Aerodynamics in gusty crosswind conditions will be of increased significance in the future vehicle development process. Recent investigations demonstrated that unsteady aerodynamic loads can exceed steady loads considerably which may deteriorate driving stability. One of the achievements of this thesis is to provide detailed information on the oncoming flow which faces a vehicle during crosswind gusts. It is proved that velocity distortions have been exaggerated in the past and pointed out which turbulence scales have to be considered instead in the future development process. This information is then used to set up an experiment that replicates realistic unsteady flow conditions, as they occur during crosswind gusts. It is verified that a delayed reaction of the wake flow to a change of the oncoming flow leads to a lateral force at the rear which increases the total unsteady yaw moment amplitude. In addition, it is shown how the intensity of this unsteady mechanism depends on the Strouhal number. In the following, the experimental database is used to validate a CFD simulation tool. Though the general characteristics of the unsteady mechanism are correctly reproduced, numerical errors appear which prohibit its application for a reliable prediction of unsteady aerodynamic loads in industry.