Free-jet experimental study on combustion characteristics of strut/cavity flameholders in a circular combustor under varying angle of attack

This study experimentally investigates the combustion processes in a circular combustor equipped with multi-stage strut/cavity flameholders. Free-jet experiments were conducted with a dynamically varying angle of attack (0°–8° at 4.09°/s) under Mach 4 inflow, while the air mass flow rate increased from 9.36 to 12.26 kg/s. The processes of the ignition, flame stabilization, and blowout were examined. The results show that the pressure in the core flame stabilization region at an angle of attack of 0° was fully established within 8.8 ms. It is significantly less time than the 26.6 ms required at an 8° angle of attack. It indicates that the high angle of attack can lead to significant ignition delay. During flame stabilization, both the instantaneous angle of attack and its history were found to significantly influence combustor pressure and flame behavior. An augmented angle of attack resulted in an enhancement in flame intensity in the proximity of the cavity floor, attributable to enhanced mixing. This effect persisted even after the angle of attack returned to 0°. Large angles of attack combined with elevated equivalence ratios triggered pronounced pressure and flame oscillations. The flame oscillation at the bottom of the cavity exhibits the highest intensity. However, the dominant frequency at all three measuring positions is 111 Hz. It suggests that combustion instability at high angles of attack is predominantly influenced by flame oscillations throughout the cavity region. During the blowout, photoelectric sensors detected the transition approximately 74 ms earlier than pressure sensors.