Investigation of a side force due to ablation

Abstract

Introduction T injection of gases by ablation or transpiration into the boundary layers of bodies traveling at high speeds can influence aerodynamic forces by altering both the skin friction and the induced pressure due to boundary-layer displacement effects. Data from flight tests of re-entry vehicles have indicated the possibility of significant Magnuslike side forces due to the combined effects of ablation, spin, and angle of attack. ] There does appear to be a definite mechanism for such a force. Due to thermal lag, the rate of ablation on a spinning body at angle of attack would be higher on one side of the body than on the other. The difference in the ablation rate on opposite sides of the body would lead to a difference in the boundary-layer induced pressure and produce a side force and moment. The side force in this case would act in a direction opposite to that of a classical Magnus force, as illustrated in Fig. 1. Recent interest in the possible effects of ablation-induced side forces on re-entry vehicle stability led to an experimental investigation in the wind-tunnel facilities of the Naval Surface Weapons Center, White Oak Laboratory. The results of this test program provide insight into the influence of several important variables, in addition to establishing the magnitude of the side force under the chosen set of test conditions.