Instabilities in rotating detonation are concerned because of their potential influence on the stability of operation. Previous studies on instability of 2-D rotating detonation mainly cared about the one of the contact discontinuity originated from the conjunction of the detonation and oblique shock. Hishida et al. first found the rippled structure existed in the interface between fresh injections and burnt product from the previous cycle (Shock Waves 19, 2009), and a mechanism of Kelvin-Helmholtz instability was suggested as well. Similar structures were observed as well in simulations by current authors, where a fifth-order WENO-type scheme with improved resolution and 7-species-and-8-reaction chemical model were used. In order to achieve a deep understanding on the flow mechanism, more careful simulations are carried out by using three grids with increasing resolution. The results show that besides the previously-mentioned Kelvin-Helmholtz instability, there are two other mechanisms which take effect in the interface instability, i.e., the effect of baroclinic torque and Rayleigh-Taylor instability. Occurrence conditions for two instabilities are checked and testified. Especially, the spike- and bubble-like structures are observed at the interface, which show appearances different from canonical structures by Kelvin-Helmholtz instability.
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