Computational Investigation of Acoustics and Instabilities in a Longitudinal-Mode Rocket Combustor

A computational fluid dynamics analysis of acoustic modes and instabilities in an experimental longitudinal test chamber is presented. The experimental configuration is a uni-element recessed injector post combined with a variable-length combustion chamber. The computations employ the nonlinear Euler equations with mass and heat addition in the injector and combustion chamber and response functions to represent combustion dynamics. Analytical solutions and experimental comparisons are used to verify and validate the computational model. The results demonstrate the importance of including the full Euler equations for predicting the frequencies and mode shapes in the injector-combustor configuration as well as for representing nonlinear phenomena such as wave steepening and the excitation of higher harmonics. The present approach therefore promises to be a useful platform for testing and calibrating combustion response functions for combustion instability models.