Analysis of the Vorticity in the Near Wake of a Station Wagon

A computational study of the turbulent flow around a modified station wagon vehicle is presented in order to predict aerodynamic forces and to understand some details of the near wake. The geometrical model was obtained by a three-dimensional scanning process but excludes some details of the vehicle such as the engine bay, and the underfloor was considered flat. A hybrid mesh (prisms' layers and tetrahedral) was generated with refinements close to the vehicle surface (including the wheels) and the near wake. The simulations were performed in the commercial software ansys fluent at a Reynolds number of 2.7 × 10⁶ based on the wheelbase. Numerical results of the drag coefficient predict values of 0.431 which is considered in fairly good agreement with the experimental result (based on a coastdown test) of 0.404. Contours of velocity, pressure, and eddy viscosity field show some important features of the separated flow in the rear part of the vehicle. A detailed study of the near wake was performed in which the evolution of the vorticity was analyzed in the downstream direction, showing several pairs of counter-rotating vortices generated from the upper part of the A-pillar, wing mirrors, and the fender of the vehicle.