Admittance function to evaluate aerodynamic loads on vehicles: Experimental data and numerical model

When a moving vehicle is subjected to cross wind, the aerodynamic loads acting on the vehicle itself depend not only on the mean value of the relative wind-vehicle velocity but also on the statistical properties of the wind, i.e. the turbulence intensity - which represents its variation in the time domain - and the integral length scale - linked to the space distribution of the wind field. This paper describes an algorithm, used to define non-stationary aerodynamic forces, which allows to account for the spatial correlation of the wind through the aerodynamic admittance function. In particular, a numerical model for the aerodynamic admittance function is developed and verified by means of comparison with experimental data. The model can be adopted for both the lateral force and rolling moment components but not for the vertical force. Finally, it will be shown how admittance depends on the geometrical characteristics of the vehicle (length and height) and on the properties of the wind, through the integral length scale.