Mechanisms Contributing to the Dynamic Stability of a Flexible Subscale Rocket Nozzle

Forced motion simulations of an overexpanded subscale rocket nozzle were performed to investigate the transient mechanisms that lead to self-exciting fluid–structure interaction as observed in preceded studies. The pressure response to the deformation could be separated into two regions upstream and downstream the flow separation position. Within these regions the transient part of the pressure was analyzed using fast Fourier transform based on the method of generalized aerodynamic forces. The amplitude spectrum and phase shift distribution of the pressure response could be explained by superposition of three independently acting mechanisms: the inclination effect, the existence of a moving axial pressure wave, and intrinsic oscillations caused by the turbulence created by the strong shock system. Simplified simulation setups using a bent flat plate and a detailed unsteady simulation of the flow in the undeformed nozzle were analyzed to validate these assumptions.