A modeling of unsteady aerodynamic forces based on the aerodynamic analyses around a simplified car model in periodic motions

Dynamic wind-tunnel tests on a simplified car model, known as the Ahmed model, were conducted using a two-degree-of-freedom model shaker. Time-resolved aerodynamic forces were directly measured with a built-in six-component balance in sinusoidal heave or pitch motions with forcing frequencies up to 8 Hz depending on the motion type. The results show that frequency-dependent magnitudes and phase differences between the model height/angle and the aerodynamic forces are in close agreement with those predicted by large-eddy simulation (LES) using an arbitrary Lagrangian-Eulerian (ALE) method. On the basis of these results, an unsteady aerodynamic force model is constructed in the form of transfer function on the assumption of linear system. The force and moment fluctuations associated with vertical motions are well described by the linear force model that integrates virtual mass and moment-of-inertia terms into the quasi steady model which expresses the posture changing rate in the form of the relative inflow angle.