Investigation on the mechanism of aeroelastic hazard during ground test of rocket nozzle

Side loads and aeroelastic stability of rocket nozzle were studied by solving Navier-Stokes equation coupled with structural equation of motion. The computation was implemented at different total pressure inlet conditions, and flow phenomena of free shock separation (FSS) and restricted shock separation (RSS) were captured. At certain total pressure inlet conditions, it was found that both kinds of separations existed in nozzle flow filed, while RSS exhibited combined space asymmetry and time unsteady characteristics. The corresponding asymmetric circumferential pressure distribution, strong pressure fluctuation in separation region and large range of displacement of shock wave all led to severe side loads. Besides, for flexible nozzles, the low pressure gradient in separation region might reduce structure stability at nozzle exit, resulting in large local deformation. It was also found that aeroelasticity exhibited buffeting characteristic due to the asymmetric separation, resulting in reduction of aeroelastic stability, even structure destruction. Moreover, aeroelasticity might amplify side loads and aggravate its growth rate. However, with increment of inlet pressure, nozzle aeroelastic stability was also increased when a full flow was nearly reached.