456 / 2019-03-10 12:08:39

On RR → MR transition in cylindrically converging shock wave reflection

Unsteady reflection,Wave transition,Pseudo-steady criterion

全体主题 > High Pressure Physics and Materials Science

In planar shock reflection, previous work proved that the transition is determined by the wedge angle. In cylindrically converging shock wave, generally, both the wedge angle and the shock intensity change as the shock propagates along a wedge. To investigate the shock intensity variation on wave transition, a special curved wedge was designed in our previous work to guarantee the wedge angle remains unvaried during the shock movement. During the converging shock moving along the specially curved wedge, its intensity becomes larger, which may result in the RR → MR transition. In our previous work, however, the variation of the shock strength is limited due to the experimental limitations, and the transition was not captured. In this work, we numerically investigate the converging shock reflecting over a curved wedge with a large computational domain, thus, the shock strength changes greatly to guarantee the occurrence of the wave transition.
It was found that for the converging shock reflection over a curved wedge, the RR → MR transition can be predicted by the pseudo-steady criterion. In other words, the unsteady flow caused by the shock intensity variation will not affect the wave transition. Actually, in planar shock reflection over a convex wedge, previous numerical work also showed that the RR → MR transition can be predicted by the pseudo-steady criterion. However, the mechanism was not presented. In this work, we first investigate a planar shock wave reflecting over a convex wedge, and the reason of application of the pseudo-steady criterion to the unsteady flow will be discussed. It is found that a rarefaction wave zone exists between the early-generated disturbances and the reflection point no matter what kind of disturbance is generated (i.e., compression wave or rarefaction wave) or what kind of flow is established (i.e., supersonic or subsonic flow). As a result, the early-generated disturbances cannot catch up with the reflection point before the sonic criterion is satisfied. For a cylindrically converging shock reflection over a curved wedge, a similar mechanism is also applicable. Further, experimental and numerical investigations of the converging shock reflection over a specially designed convex → convex wedge are performed to validate this viewpoint.