Flame and Shock Dynamics of a Sonic Jet in Supersonic Crossflows: Quenching, Shock-Vortex Interaction, and Flame Anchoring

The flame and shock dynamics of a sonic hydrogen jet injected into a confined, supersonic crossflow (Mach 2.7) are investigated. A parametric study across jet-to-crossflow momentum flux ratios (J=1.5,3.0,5.87) reveals a systematic pathway to global thermoacoustic instability. At low J, the flow is stable, characterized by coherent shock trains and weak vortices. Increasing J strengthens the counter-rotating vortex pair and Kelvin-Helmholtz rollers, which begin to deform and subsequently disrupt the shock train. At the highest J, violent shock-vortex interaction breaks down global pressure separation, generating chaotic dilatation fields. This process provides the nonlinear energy source that, as shown in prior work, feeds a domain-filling global mode. The study also resolves a longstanding debate on flame quenching. In this confined configuration, expansion regions emerge inherently downstream of the shock train. Analysis of Damkohler numbers, strain fields, and HO ₂ radical maps demonstrates that while flame quenching is spatially coincident with these expansions, the fundamental cause is the excessive strain and high scalar dissipation rates sustained by the intense vortical structures (CVP, KH rollers) within them. Thus, expansion regions mark susceptible zones, but vortex-driven strain executes extinction. This finding reconciles previous contradictory explanations by showing that Gamba's ramp-induced expansion fan and the intrinsic expansions observed here both create environments where vorticity-mediated strain dominates quenching. Flame anchoring evolves from a two-dimensional, wall-attached sheet at low J to a three-dimensional structure at high J, distributed by shock-enhanced sidewall mixing and vortical redistribution from a reorganized horseshoe vortex system.