Response of a gas-gas shear coaxial injector to transverse instability

The objective of this study was to measure the response of a gas-gas injector to velocity perturbations through CH* emission intensity at a range of instability levels and to provide quality data for comparison with high-fidelity models. To achieve this, an optically accessible, 2-D combustion chamber which self-excites a transverse instability was modified to incorporate a gas-gas shear coaxial injector at the location which coincides with the 1W velocity anti-node in the chamber. By changing the driving injector orientation, different levels of instability were produced, ranging from 8% to 65% of the mean chamber pressure. Filtered high speed video was used to measure CH* chemiluminescence, which was used to provide insight into the coupling processes which drive instability. Several diagnostics were used in the analysis of the CH* video, including the root mean square (RMS) of each pixel over the data interval and the Rayleigh Index. CH* videos synced with pressure and velocity waveform videos provided further insight into the conditions within the chamber and the corresponding injector response, and provided parameters to compare with high-fidelity models. Finally, the relationship between CH* intensity and pressure/velocity perturbations was examined using several methods with the hope of identifying relationships that could be used to develop transfer functions. However, a more thorough investigation of the relationships is needed before this is accomplished