Vortex-shedding phenomena in solid rocket motors

Abstract

In the past 20 years, periodic vortex shedding as a source of acoustic energy inside solid propellant rocket motors has been continuously studied, in connection with several motors that exhibited oscillatory behaviors although they were predicted stable by means of conventional linear stability methods. On that subject, correlations through Strouhal numbers are commonly used. In this article, the meanings of various Strouhal number definitions are discussed. The basic mechanisms for sound production in ducts or chambers are then discussed through simple tools, such as the linear hydrodynamic stability analysis, Flandro's method and the acoustic balance technique, which provide good insights into the physics of the phenomenon. Necessary conditions for vortex-shedding-driven motors are then arrived at and illustrated by actual firing results. Finally, the full numerical approaches are shown to provide unprecedented insight into the mechanisms behind the vortexshedding phenomenon and are believed to open the way to quantitative predictions of frequencies and oscillatory levels.