Prediction of surface heating of a projectile flying in RAMAC 30 of ISL

摘要

In a ram accelerator a sharp-nosed-body flies at supersonic velocity through a tube initially filled with a highly compressed combustible gas mixture. By shock compression, i.e., by the bow wave and its reflections at the tube wall, the gas mixture is heated progressively so that it becomes ignited in subdetonative combustion mode at the body's back and in superdetonative mode, investigated mainly in the RAMAC 30 of ISL, in the slit between the projectile midbody surface and the tube wall. The gas combustion causes a temperature rise follwed by a gas pressure increase giving a forward thrust to the body of the ram-projectile. Due to the transfer of heat from gas to projectile, the latter's surface temperature increases, on the one hand in the nose region and on the other hand at the body contour of the mid-part "body" region including fins and at the afterbody "expansion zone". Then ablation of surface material begins which is naturally undesirable not only at the sharp nose but also at the fins and the body of the ram projectile, especially when combustion is localized at the body of the projectile in superdetonative mode. The control of the heating at the nose and the body is necessary for successful ram accelerator operation. Therefore a prediction of the heat flux from gas to projectile surface becomes needful. For this reason a boundary layer and ablation model has been developed by which the heating of the projectile and its melting ablation at nose, fins and body can be estiamted for an optimal choice of projectile material at a desired velocity and gas pressure range.