Numerical simulation of the effect of component deformability on the aerodynamic performance of a vehicle

Aerodynamic have a huge impact on the performance of a vehicle in terms of fastest “lap-time”, but also on the reduction of the fuel consumption and of the exhaust gas emissions, primarily at high speed. The vehicle's ability to cut through the air plays a crucial role in the total efficiency of the car. With this thesis, it is tried to obtain deeper and clearer knowledge on what is happening when a car is moving through the air. The aim of this research consists of understanding the effects of the aerodynamic loads on the final aerodynamic performances of the vehicle. It is clear that, generally, a force applied on an object means that there will be an answer by the object itself. Depending on the value of the force and on the material properties, the object can be deformed or can resist without visible deformations. In the aerodynamic field, in general, the forces are seen only from the structural point of view, but their effect on the final performances is not considered. Through this research it is possible to compare the traditional approach, where the deformations are neglected, with a new one. Over the years, the numerical simulations in every field try to be more and more realistic. This thesis is an attempt to make a further step to obtain more reliable results from the CFD simulations. The impact of the external deformations caused by the aerodynamic forces will be investigated. This methos is called FSI (fluid structure interaction) and it is becoming more and more important in a lot of sectors. This is because, as already said, the application of a force on a surface could mean deformation of the surface itself, but different shape means different aerodynamic performances. As quite always happens in the automotive world, the analysis will start from the study of a sport car and, only after, it will be transferred on the development of the normal passenger cars. The component under analysis is the rear wing of the Alfa Romeo Giulia GTAm. The results will help to understand if it can be useful to bring this kind of research in the development of all the vehicles or if, instead, the influences are so small to be considered negligible. The method that will be followed is an iterative process that starts from the simulation of base non-deformed model. From this simulation, the external forces acting on the rear wing are extrapolated and the Finite Element Method model with the deformations is calculated. Finally, the external geometry is modified based on this FEM model and a new simulation is performed to obtain the new aerodynamic coefficients. This loop is done until the deformations become negligible, from the aerodynamic point of view, or if the material collapses. In general, during the development of the passenger cars, all this process is done only one time, to ensure structural resistance of the components. This research has been done thanks to the know-how and the instruments given by the CFD team of the Stellantis group. The software that will be used are ANSA and Star CCM+ for the aerodynamic analysis.