Usteady Flow Measured in a Mixed-Flow Type Vaneless Diffuser System

Abstract

The instability of the flow through a mixed-flow-type vaneless diffuser system was examined experimentally. An unsteady flow was observed when the angle of the flow at the diffuser inlet became small, and it was concluded that the unsteady flow was based on rotating stall occurred in the vaneless diffuser. The effects of the diffuser width and inlet pipe on the rotational speed of the stall cell were observed. Rotating stall measured in this study was different from that reported for radial vaneless diffusers. The rotational speed of the stall cell, however, is nearly equal to that measured for the radial vaneless diffusers. The flow condition in the vaneless diffuser at the initiation flow rate of rotating stall was discussed based on the velocity distributions measured and those obtained from a turbulent flow analysis.