Evaluation of vortex shedding phenomenon in a sub-scaled solid rocket motor

Abstract

Pressure oscillations are one of the most important challenges of high slenderness ratio solid rocket motors. The cause of these oscillations can be traced to the vortex shedding due to grain burning areas, holes and slots. In this paper, a four segments grain of space shuttle boosters and the structure of Ariane 5 small-scale motors are used to evaluate aeroacoustic pressure oscillations. First, the related parameters to scale down were determined using Buckingham's Pi-theorem, and then a small-scale 1:31 motor was designed and manufactured. Next, the number of Strouhal in different grain forms and the prediction criteria of vortex shedding were discussed. In the next step, to understand the internal flow of the motor and the formation of vortex shedding, the dynamic calculation of the steady state computational fluid was performed in seven regression steps and finally, two static tests were performed to validate the analysis and simulation. The results show that different definitions for the Strouhal number are useful only for the first glance at the vortex shedding and pressure oscillations, and therefore the CFD solution and test program for a correct understanding of the ballistic operational condition of the motor is inevitable. In addition, despite aggress of pressure test data and grain-burning regression of sub-scaled motor to full-scale motor, the internal flow phenomenon may be different from the scale motor due to its small-scale time and dimensions.