Numerical simulation on acoustic mode and pressure-oscillation decay in finocyl- and axil-grain combustion chambers

Abstract

Combustion instability has long been one of the severe problems suffered by solid rocket motors (SRMs). Currently, acoustic instability is one of the most widely researched classifications in the field of instability combustion. This study focuses on the differences in the acoustic characteristics and the decay characteristics of the pressure oscillation excited by pulses between finocyl- and axil-grain combustion chambers. A method is proposed for the suppression of the acoustic instability combustion. The finocyl- and axil-grain combustion chambers were investigated via an acoustic finite-element analysis and computational fluid dynamics (CFD). The ideas of time–frequency joint analysis and pressure-pulse decay were applied to study the acoustic field and oscillating flow field in the combustion chamber. The results of the acoustic harmonic response analysis and CFD calculations indicated that the axil grain is more stable than the finocyl grain in low-order acoustic modes. The time-weighted average response amplitudes at the 1st-order acoustic frequency for the axil-grain motor at the combustion-chamber head and end were 54.8% and 75.4%, respectively, of those for the finocyl-grain motor.