Pressure and Velocity Fluctuations in the Diffuser for Rotating Stall Period

This study describes details on local reverse flow patterns in a vaneless diffuser by experiments through PIV measurement technique in the water bath during the unstable operation of a compressor with radial impeller. In order to do these measurements, the pressure transducers were installed on the hub wall with several diffuser radius ratios and they were synchronized with the velocity images of CCD camera. Especially we tried to make them synchronize with time during rotating stall period. For relatively high and low pressure instants, we observed and discussed how the radial and tangential velocity components fluctuated.