Slender-Body Aerodynamics for High-Speed Ground Vehicles

Abstract

Classical slender-body theory for the prediction of the steady-state aerodynamic characteristics of high-speed ground vehicles of arbitrary cross section is presented. Special consideration is given to the effect of a side wind. The effectiveness of side fences in providing aerodynamic shielding from a side wind is treated in an approximate manner. Specific analytical relations and normalized parametric curves are presented for vehicles having similar semielliptic cross sections. The theory indicates that, for an unshielded vehicle, a side wind introduces a significant lift force which is proportional to the square of the yaw angle and the projected side area of the vehicle. For unshielded vehicles with a truncated aft end, the side force and rolling moment vary linearly with yaw angle, and to the first and three-halves powers of the aft-end area, respectively. The side force decreases and the rolling moment increases with decreasing vehicle height-to-width ratio. For smoothly closing aft ends, there is no side force or rolling moment. In general, small-to-moderate shielding is ineffective in reducing the lift due to side wind, small shielding is slightly effective and moderate shielding quite effective in reducing the rolling moment, and small-to-moderate shielding very effective in reducing the side force. Comparisons with some preliminary wind-tunnel tests on unshielded ground vehicles of semicircular cross section show fairly good agreement.