Numerical study of periodic flame flashback in a cavity-based scramjet combustor

The periodic flame flashback phenomenon in an ethylene-fueled cavity-based scramjet combustor was numerically investigated by a three-dimensional unsteady Reynolds-averaged Navier–Stokes solver with two-step kinetics. air inflow stagnation temperature is 1225 K, and its Mach number 2.6. Spectral analyses revealed the combustion oscillations flashbacks maintained separated mode establishment/vanishment of flow separation near fuel injector, differing from previous studies connected to ramjet/scramjet transitions. A mechanism four evolution stages proposed elucidate flow-flame interaction. In stage I, rapid upstream shock-train extension were caused high-temperature induced auto-ignition tendency well-mixed unburned gas near-sidewall low-speed region. II, combustion-induced back pressure shock train gradually achieved aerodynamic balance. barely changed III. Meanwhile, simplified model suggested that gradual rises occurring cavity away sidewall spanwise heat conduction. higher temperatures would cause propagation enhanced release due auto-ignition. However, occurred mostly subsonic flow, resulting decreases according one-dimensional equations. smaller produced lower back-pressures, which prompted recession downstream IV. Moreover, flame-spreading illuminate nature. comparison speeds theoretical estimations indicated current regime turbulent propagation, rather than C–J detonation or deflagration speculated studies.