Unstable combustion induced by oblique shock wavesat the non-attaching condition of the obliquedetonation wave

摘要

The instability of oblique shock wave (OSW) induced combustion is examined for a wedge with a flowturning angle greater than the maximum attach angle of the oblique detonation wave (ODW), where archivalresults rarely exist for this case in previous literatures. Numerical simulations were carried out forwedges of different length scales to account for the ratio of the chemical and fluid dynamic time scales.The results reveal three different regimes of combustion. (1) No ignition or decoupled combustion wasobserved if a fluid dynamic time is shorter than a chemical time behind an OSW. (2) Oscillatory combustionwas observed behind an OSW if a fluid dynamic time is longer than a chemical time behind an OSWand the fluid dynamic time is shorter than the chemical time behind a normal shock wave (NSW) at thesame Mach number. (3) Detached bow shock-induced combustion (or detached overdriven detonationwave) was observed if a fluid dynamic time is longer than a chemical time behind a NSW. Since no ignitionor decoupled combustion occurs as a very slow reaction and the detached wave occurs as an infinitely fastreaction, the finite rate chemistry is considered to be the key for the oscillating combustion induced by anOSW over a wedge of a finite length with a flow turning angle greater than the maximum attach angle foran ODW. Since this case has not been previously reported, grid independency was tested intensively toaccount for the interaction between the shock and reaction waves and to determine the critical time scalewhere the oscillating combustion can be observed.