Local aerodynamic optimisation and drag reduction for a sedan at late stage styling

An automatic optimisation process was devised based on a 1/2 scale sedan to improve local aerodynamic shape and reduce wind resistance. Computational fluid dynamics (CFD) simulations were used to verify grid independence. The appropriate design of experiments (DOE) algorithm, fitting model, and optimisation algorithm are selected depending on local shape complexity and its influence on drag coefficient, and important shapes are optimised for multivariable deformation. Vehicle drag coefficient was reduced by 1.23%, 1.85%, 3.09%, and 7.12% after optimising front and rear fenders, A-pillars, and trunk lid, respectively. Main effect analysis enabled studying weight influence for each variable on drag. The interaction diagram shows mutual influence from reducing drag for each variable. Thus, reducing overall drag cannot simply superimpose local optimisation effects due to interactions between local flow fields.