Investigation of the Flame-Acoustic Wave Interaction during Axial Solid Rocket Instabilities

Primary research objectives are to 1 investigate mechanisms responsible for driving of axial instabilities by solid propellant flames 2 determine whether state-of-the-art theoretical models can predict characteristics of the flame driving mechanisms and 3 investigate the effect of flow turning upon axial instabilities in solid propellant rocket motors. To attain these objectives, the response of diffusion flames, stabilized on the side wall of a duct, to imposed acoustic waves was investigated by using flame radiation measurements and laser Doppler velocimetry LDV. Flame radiation measurements revealed that the presence of an acoustic field produced space dependent oscillatory heat release rates which depend upon characteristics of the flame and the excited acoustic field. Measurements of flame radiation and velocity field both showed that at a given instant some sections of the flame drive the acoustic field while others damp it. The net effect of the flame upon the acoustic field depends on the relative magnitude of these driving and damping regions. Validity of a previously developed flame response model was investigated by comparing measured and predicted oscillatory velocity components in the flame region. Using measured values of the acoustic admittance of the burner, flame shape, and steady state temperature distribution in the flame region, the model was used to predict oscillatory vertical velocity distributions in the flame region. These were then compared to velocity distributions measured with an LDV system, showing good qualitative agreement.