Effects of cavity position and structure on pulsed pressure oscillations

In order to research the effects of cavity position and structure on pulsed pressure oscillations, four kinds of rocket motor models with different cavities were numerically studied via Fluent along with UDF(User Defined Functions). The flow structures and pulsed pressure oscillation characteristics were obtained, which can provide theoretical guidance for the design of grain structure and suppression of combustion instability. The results indicate that head end cavity is contributed to suppressing combustion instability. Middle cavity can easily induce vortex-driven-pressure oscillations, and the convergent middle cavity is better than divergent middle cavity in terms of the motor stability. After end cavity is harmful to motor stability because the end cavity can reduce the nozzle damping and induce vortex shedding under the pulsed condition. Therefore, the finocyl-end grain structure should be carefully considered in engineering design.