Eventos Anais de eventos
COBEM 2021
26th International Congress of Mechanical Engineering
CFD-based multi-objective aerodynamic optimization of a car rear diffuser
Submission Author:
Bruno Carmo , SP
Co-Authors:
Denis Peixoto, Bruno Carmo
Presenter: Bruno Carmo
doi://10.26678/ABCM.COBEM2021.COB2021-1689
Abstract
The lift coefficient plays an essential role in high-performance cars like race cars to improve the overall downforce and consequently maximize the car grip. Higher grip provides more safety during car handling and increase the lateral acceleration of the vehicle during the corners, which is a factor that contributes decisively to reduce the overall lap time. By reducing the drag coefficient, it is possible to achieve higher top speed and improve the car's fuel efficiency. In this work, computational fluid dynamics (CFD) is employed as a tool for the aerodynamic optimization of the geometry of a car rear diffuser, aiming to minimize drag and lift coefficients. Due to the ground effect, the rear diffuser can generate a high downforce level without a substantial drag penalty. The three-dimensional CFD simulations were performed for half-model, taking advantage of the longitudinal symmetry. We solved the flow considering steady state and employed the k-omega shear stress turbulence (SST) model. Ground effect was considered, and some simplifications were made to the geometry to make the numerical simulations possible, the most important of them was to neglect the wheels. A mesh convergence analysis was carried out, employing the grid convergence index methodology. Lift and drag coefficients were optimized with respect to the length and maximum height of the diffuser, and the meta-heuristic FAST method was employed as the optimization tool. A pareto front was obtained, and one of the designs was chosen to have its flow field analysed and compared to the data obtained from simulations of the flow around the car without the diffuser. That optimal design chosen exhibited an increase of 164% in the absolute value of the lift coefficient (downforce), with a penalty of 16% in the drag coefficient, when compared to the car without the diffuser. The behaviour of flow quantities in the wake and distribution along the car surface could be correlated to the change of the force coefficients, leading to some physical insights in the complex flow that happens around the car.
Keywords
Vehicle aerodynamics, Computational Fluid Dynamics, Drag, Lift, Multi-Objective Optimization
