Experimental investigation of combustion pattern formation in cavity-stabilized supersonic flows

Scramjet engines utilize cavity-based stabilization mechanisms to maintain combustion within millisecond-scale residence times under extreme flow conditions. However, the interaction between complex physical processes within the system frequently drives the system into combustion instabilities, thereby reducing performance and threatening structural integrity. This study experimentally investigates the formation of combustion patterns in a cavity-stabilized supersonic combustor. Through high-speed pressure and CH* measurements, we identify distinct combustion states as the global equivalence ratio (Φ) increases: aperiodic oscillation at low Φ (0.3), intermittent oscillation at intermediate Φ (0.6), and synchronized periodic oscillation at high Φ (0.9). Cross wavelet transform reveals distinct transient phase coherence between pressure and heat release rate, while convergent cross mapping establishes causal relationships, confirming bidirectional causality at high Φ. High-speed flame imaging visually corroborates the transition from aperiodic to synchronized combustion via the intermittent state. The dynamics are interpreted via the Kuramoto model, which successfully characterized the intermittent synchronization behavior phenomenologically, illustrating that the supersonic combustion in scramjets constitutes a multi-oscillator system. Similar transition patterns have been reported in subsonic combustors, suggesting potentially universal synchronization mechanisms.