Numerical investigation of oscillatory instability in shock-induced combustion around a blunt body

The basic characteristics of oscillatory instabilities of shock-induced combustion around a spherical projectileflying at hypersonic speed is investigated on the basis of numerical simulation using a two-step chemical reaction model. A series of simulations is conducted to understand the mechanism of these oscillatory instabilities. The oscillatory instabilities are clearly observed when the projectile radius is about 7.5-10 times the induction length. Examination ofthe computed result shows that the oscillatory instability is created by the wave interaction between the bow shock waveand the stagnation point of the body surface. It is clarified that the oscillatory period is closely related to the balance between a shock stand-off distance and an induction reaction length; i.e., the instabilities are caused not only by the wave interaction between the bow shock and the reaction front but also by the compression wave reflected from the stagnation point of the projectile surface toward the bow shock.