Thrust Optimization of a Projectile Flying at Hypersonic Speeds in an External Propulsion Accelerator

Shape optimization of a projectile flying at hypersonic speed in a chemically reacting flow with computational fluid dynamics, is presented. The application is a so called external propulsion accelerator, in which a ballistic configuration is accelerated through a premixed combustable medium. The projectile uses a ring design, flying at hypersonic speeds through a detonable mixture, to generate a detonation wave, initiating combustion along the rear surface of the projectile, achieving positive thrust. However, drag and propulsive forces are of the same order of magnitude and small changes in the design can have a large effect on the net thrust of the projectile, making an accurate calculation necessary. The dynamics of the combustion over the projectile are such that only computational methods are sufficient to model the flow field. A scheme is developed utilizing a combination of both high cost and low cost CFD methods, resulting in a suitably accurate, medium cost method for calculating the resulting flow field around the projectile. This model is then implemented in an optimization scheme to develop a projectile shape that is desired for maximum net thrust. The resulting configuration provides an over 40% increase in the net thrust on the projectile.