Comparison Between Simulation and Measurement of Self-Excited Combustion Instability

Combustion instability arises from the coupling between unsteady combustion and acoustic modes in a combustion chamber. A study comprising concurrent experiment and LES simulation of a single element rocket combustor was conducted. The goal was to evaluate the a priori predictive ability of the computational model with regards to self-excited combustion instability, and to use the detailed results from the simulation to interpret the mechanism of self-excitation. Pressure modes and chemiluminescence from CH* were measured at high sampling rates. Direct comparisons between the experimental and computational results were made on the basis of instability frequency, pressure mode shapes, and limit cycle amplitude. All indicated generally good agreement. The light emission representing heat release from the experiment was qualitatively similar to the simulation. The detailed results from the simulation provided much greater insight into the complex phenomena, and showed the likely mechanism that drove high amplitude instability was a periodic ignition in the recirculation zone just downstream of the dump plane. The ignition occurred nearly simultaneously with the arrival of a compression wave traveling from downstream.