Secondary injection in a model solid rocket motor for the suppression of vortex-driven instability
Cold-flow, secondary-injection experiments were conducted for the active control of vortex-driven instabilities seen in solid rocket motors. Twin orifice plates located within a 5-cm-square, 86-cm-long airflow chamber produced the vortex shedding and impingement mechanism. These were used to excite a standing-wave pressure oscillation at the first longitudinal mode near 200 Hz. A novel secondary injector, located at the front end of the chamber, utilized the compressed air from a modified, 2-stroke model airplane engine powered by a controllable DC motor. The response of the cold-flow chamber to the new secondary-injection technique was characterized over a range of injection frequencies from 50 to 210 Hz and relative perturbation flow rates up to 16% of the total chamber flow. An inviscid, theoretical model of the chamber response to an ideal secondary injector was used to estimate the efficiency of the present setup. The model predicts that the secondary injection scheme generates pressure-wave amplitudes that are either 17 or 26 times (depending on exit nozzle area) larger than the injected perturbation wave. Open-loop control experiments were conducted by pulsing the secondary injector near the frequency of the organized chamber-pressure oscillations with arbitrary phasing. The ability of the secondary injection scheme to suppress vortex-driven pressure oscillations was demonstrated. The data also suggest that the secondary injection may have an effect on the vortex-shedding mechanism itself, particularly at injection frequencies near a chamber acoustic mode. © 2000 by The Aerospace Corporation.
author list (cited authors)
Petersen, E. L., & Murdock, J. W.