Computational fluid dynamics analysis of a lateral mirror and introduction to digital implementation

Nowadays, lateral mirrors, along with other car components, are in the spotlight of automotive experts, who are trying to modify the geometry of these components so as to reduce the aerodynamic drag and therefore save fuel. The aim of this project is to go in-depth into the world of Computational Fluid Dynamics (CFD) by means of an aerodynamic study of the lateral mirrors of a generic car. The software used for the study is ANSYS Fluent. As any other CFD simulation, this study consists of the following steps: generation of the geometry, meshing, selection of the boundary conditions and the physics of the problem, realization of the CFD simulations and post-processing and analysis of the results. The first challenge in this project was to choose carefully the dimensions of the fluid domain around the car. Ideally, the control volume must be as big as possible for obtaining the most accurate results. Unfortunately, the bigger the fluid domain, the higher the computational cost. Meshing, or splitting the control volume into pieces called cells, is without doubt the most difficult step. It was possible to achieve very small cells near the narrower and sharper geometry surfaces. Far from the geometry, the cells generated are bigger since fluid properties change tardily. Two kinds of geometry were simulated: 1) a car with lateral mirror and 2) a car without lateral mirror. The drag and lift forces were obtained from the simulations. It can be concluded that, when the lateral mirror is removed from a car, the drag is reduced and the lift increases (in the sample car used in the study, the reduction and increase is by 1.4% and 7.7%, respectively). Finally, a solution to the problem associated with driving a car without lateral mirrors was investigated. In order to do so, several videos were captured with a wide-angle camera from the lateral mirror position. These videos were processed and, by means of a simple Matlab code, a program was developed to establish whether or not an overtaking is occurring.