Relation between shock unsteadiness and the origin of side-loads inside a thrust optimized parabolic rocket nozzle

An experimental test campaign has been carried out on a sub-scale thrust optimized parabolic (TOP) nozzle to study the relation between unsteady characteristics of separation and reattachment shocks and the origin of side-loads in rocket nozzles. The study was conducted using wall pressure measurements both in streamwise and circumferential directions, surface oil visualization technique and signals from strain gauges installed on the nozzle bending tube. It is observed that the nozzle pressure ratio at which peaks in maximum rms values occur, for separation and reattachment shocks, coincide with the nozzle pressure ratio at which peaks in strain gauge signal are observed. This clearly demonstrates the unsteady nature of separation and reattachment shocks to be directly related to origin of side-loads in rocket nozzles.