Studies on Ignition Over Pressure Characteristics Related to Typical Launch Vehicle Lift-off

Abstract

The ignition over pressure (IOP) is an unsteady pressure wave generated during the launch vehicle lift-off at the ignition of large solid rocket boosters. This IOP behaves as a blast or a shock wave characterized by a positive triangular-shaped first pulse succeeding relaxation wave with negative half-sine wave form. This pressure pulse moves upward along the vehicle and its surroundings, which might cause severe damage to the structure due to its low frequency oscillations of the order 20 to 40 Hz. These low frequency oscillations will pose serious problems on structural integrity of the launch vehicle and payloads with large surface area. In the case of a launch vehicle ground lit propulsion system, having two huge solid rocket boosters, small skew in the ignition delay of two boosters produces two ignition over pressure pulses having time lag between them, which could induce severe toppling moment on the vehicle. The present paper deals with the occurrence of such blast waves during the firing of various scaled-down solid rocket motors and associated IOP effects and its scaling. An attempt also has been made to compare the numerical simulation of IOP wave and comparison with the experiments.