Flow investigation of a low-speed-operated centrifugal compressor over a flow range including zero flow

A centrifugal impeller with back-sweep-blades, followed by a vaneless diffuser, r/r(2) = 2.5, was tested at one-fifth of its design speed. As expected, its overall performance curve consisting of negative and positive slopes had great similarity to the performance of centrifugal pumps. It showed no sign of significant instability as it was run up to shut-off-condition. A centrifugal compressor inducer is known to be very sensitive to incidence change. In this investigation, it was expected that significant incidence losses and eventually incidence stall due to the high incidence, resulting from the wider range of operation, could be generated. In addition, the diffuser was also expected to be a source of instability. However, both the inducer and the diffuser were relatively stable; the flow mechanism responsible for this is examined.