Stability of spinning detonation waves

The present paper reports the results of a study of the stability of spinning detonation near the detonation limits. The detonation velocity as well as the structure are observed for long distances of propagation. Stable mixtures (with regular transverse wave pattern) and unstable mixtures (with irregular transverse wave pattern) are investigated. It is found that the local velocity fluctuates as the spinning detonation propagates and the fluctuations increase when past the first onset of spinning detonation towards the limits (failure). For stable mixtures of C2H2+2.5O2C2H2+2.5O2 with high argon dilution, the fluctuations are less than for unstable mixtures of C2H2+5N2OC2H2+5N2O and CH4+2O2CH4+2O2. Limits are indicated by abrupt failure of the detonation after some distance of propagation. Long smoked foils (∼3 m) indicate that the spinning structure is not constant, but varies periodically as the detonation propagates. Past the first onset of spinning detonation, the fluctuation in the spin structure occurs more frequently and failure is evidenced by the disappearance of transverse waves trajectory on the smoked foil. For stable mixtures, the spinning detonation structure is more stable with a constant pitch and a well defined straight trajectory of the “spin head”. However for unstable mixtures, the spinning detonation is more unstable with varying spin pitch and a “wavy” trajectory of the “spin head”. Also extraneous modes appear periodically superimposed on the spin mode. Subjecting the detonation to a finite perturbation narrows the range in which spinning detonation can be observed. In general the detonation suffers a disruption both in the structure and velocity but recovers after some distance downstream of the obstacle. However for the very unstable mixture of CH4+2O2CH4+2O2, it is found that past the limits, abrupt reinitiation occurs downstream of the obstacle similar to the phenomenon of the onset of detonation as in DDT.