Combustion Response Measurements of a Transverse Instability Combustor

Combustion instability in rocket engines has been a significant problem that has been studied for decades. Modern computational models have potential in creating simulation software that can help facilitate engine development with lower risk and cost, but requires high-fidelity validation data and analysis to create. The transverse instability combustor (TIC) is a modular test combustor with optical accessibility to three configurations of injector spacing that can be used to obtain chemiluminescence data for the development of flame transfer functions (FTF). These functions can serve as a foundation for reduced order models of transverse injector arrays. The test campaign provided a large amount of pressure and optical data that was analyzed to create FTFs. These FTFs show a relationship between the light intensity, which is representative of heat release through chemiluminescence, and pressure oscillations of the combustion field. This relationship follows Rayleigh\u27s Criterion of coupling and growth of the two oscillations, resulting in unsteady and unstable combustion behavior. The tests of the TIC were characterized using FTFs into three stability levels, with some tests that contain growth periods of instability. Multiple methods of developing the FTFs were utilized, including global frame averaging, dynamic mode decomposition, and transverse velocity reference signals. Differences in the combustion response potentially due to injector spacing changes were also analyzed. An investigation into optical data acquisition devices for FTFs was also performed. The TIC used both a high-speed camera and a photomultiplier tube to measure light intensity. The relative merits of each device are discussed based on the FTFs created from each optical data set