Flow control of rotating stall in a radial vaneless diffuser

Abstract

The instability of a back flow layer on a diffuser wall and that of a main flow with vorticity have already been pointed out theoretically as the cause of rotating stall in a vaneless diffuser. Each instability of the back flow and the main flow, however, has not yet been proven experimentally. This study was carried out to examine the cause of rotating stall in a vaneless diffuser. The air jet from a small nozzle was used to control rotating stall in the diffuser. Rotating stall was completely suppressed by the jet in the opposite direction to the impeller peripheral velocity vector, and amplified by the jet in the same direction to the peripheral velocity vector. The cause of rotating stall and the mechanism for the suppression/amplification are discussed based on the experimental result.