Moving Model Investigation of Unsteady-Crosswind Ground-Vehicle Aerodynamics / Untersuchung instationärer Seitenwinde in der Aerodynamik bodengebundener Fahrzeuge anhand der Methode bewegter Modelle

Abstract

A vehicles performance, efficiency and safety depends on the aerodynamic conditions it is operating in. Unsteady aerodynamic conditions, such as gusty crosswinds, come with sudden yaw and force transients that can lead to path deviation and fatal accidents. A better understanding of these unsteady conditions is thus fundamental. This work analyses unsteady crosswind events, using a cutting-edge moving-model facility at the German Aerospace Center (DLR) in Göttingen, in which a generic vehicle model is accelerated on a track along a perpendicular side-wind tunnel. A static wind-tunnel setup is used for comparison. Evaluations of the unsteady surface pressures, transient forces and salient flow structures between the steady and unsteady case are compared. Peaks and extended maxima in the force coefficients in the moving-model analysis were found to overshoot the values from the steady analysis. These results suggest that realistic, unsteady crosswind encounters lead to temporary higher forces as steady investigations might predict. Therefore steady-state crosswind simulations can only be taken as a first approximation for the problem, but further investigations should be conducted with unsteady-state-simulating facilities, like the moving-model facility.