Dynamic pressure measurement on the shroud wall for a high performance single stage centrifugal compressor has been implemented to record the unsteady pressure data during rotating stall. Apart from the frequency analysis of the stall characteristics, a computer-aided method has been developed to enable the unsteady internal pressure patterns inside the blade channel near shroud surface to be described and shown in an animated visualisation.

Typical results of internal pressure patterns for a backswept impeller with two cell rotating stall occurrence at the impeller speed of 16000 rpm are presented in detail. The internal flow structure can be interpreted by pressure patterns of three types emerged consecutively within one time period of stall pressure oscillation: the normal pattern, the mixed pattern and the stalled pattern. The mixed pattern is characterized by a coexistence of the reverse movement of high pressure region towards inlet and the inlet separation. The stalled pattern is characterized by a collapse of pressure loadings in the blade channel. Such observation is thought to be useful for exploring the flow mechanism of rotating stall.

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