  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.
