LIQUID ROCKET COMBUSTION CHAMBER-CHARACTERIZATION OF THE ACOUSTIC BEHAVIOR TO AVOID COMBUSTION INSTABILITIES

摘要

Over the last 40 years, many solid and liquid rocket motors have experienced combustion instability. Combustion instability is the interaction of the inherent oscillatory acoustic modes with the combustion and/or fluid dynamic processes inside the combustion chamber. Studies have been showing that, even if less than one percent of the available energy is diverted to an acoustic mode, combustion instability can already be generated. On one hand, this instability can lead to ballistic pressure changes, couple with other motor components such as guidance or thrust vector control, and in the worst case, cause motor structural failure. In this case, measures, applying acoustic techniques, must be taken to correct/minimize these influences on the combustion. On the other hand, combustion instability, although present, does not cause system problems and can be tolerated. In this case, it still must be characterized and understood. This paper describes the applied procedures to characterize the acoustic behavior in the inner cavity of four different configurations of a combustion chamber. The simple analytical models are generated and the calculated acoustic resonances are compared with the measured acoustic natural frequencies, using cold flow inside the chamber cavity. Some comments about the measurement procedures are done, as well as the next steps for the continuity of this research.