To Investigate Obstacle Configuration Effect on Vortex Driven Combustion Instability

Abstract

Combustion instability inside a chamber may lead to catastrophic failure. It is due to inappropriate combustion or flow physics. Flow-driven instability is mostly governed by surface, corner, or obstacle vortex shedding. Inhibitorsare placed inside a solid fuel combustion chamber to control the burning of the solid fuel grain. They burn slowly as compared to solid fuel and create protrusions inside the combustion chamber. These protrusions work as flow obstacles. An obstacle vortex is shed from the inhibitor and produces pressure oscillations. The effects of inhibitor position on pressure oscillation inside a solid fuel combustion chamber is investigated in the present study. Large eddies must be resolved to compute vortex-driven flow. Therefore, the Detached Eddy Simulation is applied to cylindrical combustion chambers having inhibitor and nozzle. Five different configurations are simulated. All parameters of different configurations are similar except inhibitor position. The inhibitor is moved upstream and downstream from the reference position to examine its effect on pressure oscillations. Pressure time histories at eight distinct places of the combustion chamber are recorded. Fast Fourier Transform (FFT) has been utilized to get pressure oscillation frequency and amplitude. It is interesting to reveal that the maximum amplitude of pressure oscillation occurs when the inhibitor to stagnation point distanceis close to the combustion chamber diameter. It is up to 70% higher as compare to reference inhibitor position results. Computed results are also compared with available experimental data for validation purpose.