Oscillation of Circular Shock Waves with Upstream Nonuniformity.

Abstract

Until to the authors' previous reports on the oscillation of circular shock waves, investigations have been concerned with situations where the upstream flow is uniform, and oscillation and deformation are induced by only downstream conditions. However in the centrifugal compressor, the flow into the diffuser becomes nonuniform due to the impeller wake and the stall in the upstream impeller, which causes deformation and oscillation of the shock wave. Here, the above effects are considered. The upstream disturbance was generated by cylindrical bars. An imperfectly circular shock wave was induced by the wake, and the oscillation state, along with the modes caused by forced oscillation, was investigated experimentally. It was found that the basic mode of oscillation is predominant and that the oscillation is weaker than in the case of a uniform upstream.