On Tyre Rotation Modelling and Cooling Flow Measurements

Licentiate thesis, 2015

With the technological computer advancements, vehicle development is relying more and more on simulations as an alternative to testing. A similar trend follows in aerodynamic development of vehicles where Computational Fluid Dynamics(CFD) simulations are increasing in complexity and accuracy. Even though these simulations have previously been used to evaluate trends of different design and analyse the flow field around the car, they are aimed at being used to predict exact figures in the future. Wheel flow aerodynamics has been the focus of CFD research for several years now especially with the expected introduction of the WLTP regulations, which will require car manufactures to evaluate the drag of the vehicle for all different rim and tyre combinations the car could have in order to determine its official fuel consumption. Thus correct and accurate modelling of tyre and rims in CFD is a high priority for vehicle manufacturers in order optimize vehicle design without large increases in testing costs. This thesis investigates the effects of different wheel geometries as well as different wheel rotation modelling techniques and their effect on overall vehicle forces. An important parameter to consider when validating simulations is the cooling flow as the amount of air going through the vehicles engine bay changes the airflow around the car thus affecting the flow directed towards the wheels. In this thesis a novel, simple, and quick method for measuring cooling flow is introduced. This allows the monitoring of cooling flow during aerodynamic development at low costs especially with the introduction of grill shutters as a further step to reduce aerodynamic drag when cooling flow is not needed.