Flame Spread with Sudden Expansions of Ports of Solid Propellant Rockets

Abstract

Detailed theoretical and experimental studies on flame spread over nonuniform ports of solid propellant rockets have been carried out. An idealized two-dimensional laboratory motor was used for the experimental study with the aid of cinematography. A detailed numerical simulation of the flame spread has also been carried out with the help of a two-dimensional Navier-Stokes solver. Experimental results showing the phenomenon of secondary ignition have been reported earlier and also reviewed here with the inclusion of additional results of a three-dimensional geometry closer to a dual-thrust motor. In this paper more tangible results including the numerical modeling of flame spread have been reported. It has been shown conclusively that under certain conditions of step location, step height, and port height, which govern the velocity of gases at the step by the partially ignited propellant surface or by the igniter gas Row, secondary ignition can occur far downstream of the step, This is very likely to be within the recirculating Row region. The secondary ignition gives rise to two additional flame fronts, one of which spreads backward st a relatively lower velocity, presumably as a result of low reverse velocities present in the separation zone. This phenomenon is Likely to play an important role in the starting transient of solid propellant rockets with nonuniform ports.