Response of a Gas-Centered Swirl Coaxial Injector to Transverse Instabilities

An accurate and mechanistic model of the way in which combustion responds to pressure and velocity perturbations at frequencies corresponding to the acoustic mode of a combustion chamber is the key to advancing our ability to avoid and control combustion instabilities. A model rocket combustor that can provide a simulated unstable environment has been developed for the measurement of the combustion response of a gas-liquid coaxial injector to high-amplitude transverse oscillations. The combined use of root mean square, Rayleigh Index and phase angle plots is presented to gain a better understanding of this response and to potentially provide validation data for advanced combustion models. The injector was inserted into the center of the unstable combustor and simultaneous high speed video images of both filtered combustion light and backlight images were captured. When analyzed together the images can give an understanding of the combustion dynamics in the chamber. Strong transverse instabilities at 2035 Hz and 4065 Hz were present in the chamber. The images were time-averaged to show the mean combustion distribution and spectrally analyzed to determine the locations of the greatest response. Rayleigh index plots were produced to determine the location of driving and damping in the chamber. Phase angles between combustion light and flow oscillations calculated to determine the temporal relationship between the heat release as indicated by combustion light and the resonant oscillations. The video images were successfully analyzed to determine the frequency, spatial and temporal location of the combustion in the chamber due to both pressure and velocity acoustic perturbations. The tests showed successful use of simultaneously capturing both combustion and backlit images with a dichroic mirror.