Importance of road model in simulation of car aerodynamics in a wind-tunnel

In wind-tunnel tests of road vehicles, the great weight has proper reconstruction of the car movement conditions. Unfortunately, certain errors are unavoidable. One of main sources of errors in a wind-tunnel testing facility is the stationary floor. In order to reduce its effect, different structural solutions are used. One of those is to equip the wind-tunnel with an elevated platform (a ground board). The boundary layer exists also on such board, but it is much thinner than on the floor. Our aim is here to determine how great is the error of solution with a board in comparison with real road conditions. In the work various numerical simulations of the flow realised in wind-tunnels with stationary ground board and simulations of idealised flow with moving ground (without boundary layer) have been carried out. The boundary conditions for flow simulations has been defined in such manner that other sources of wind-tunnel testing errors have been eliminated. In simulations has been used own software for solution of viscous, incompressible flows described by the Navier-Stokes equations. The solution method is based on a finite volume approximation connected with adaptive mesh refinement. Selected results of flow simulations show effects of the stationary board on the car aerodynamics for different body shapes. It has been also analysed the effect of other parameters, such as the underbody clearance gap or viscosity.