Detection of Rotating Stall in a Centrifugal Blower : Analysis of Wall Static Pressure Fluctuation

The transient process on rotating stall in a centrifugal blower with a backward-leaning blade impeller was measured in the impeller and in the vaneless diffuser by means of the high-response pressure sensor as well as the semiconductor laser 2-focus velocimeter. It is shown that a small intermittent fluctuation, which is called prestall, occurs prior to rotating stall due to the interaction between the impeller passage flow and the diffuser wall flow under the condition of radially inward flow in the vaneless diffuser, and prestall develops into rotating stall with decreasing flow rate. The focus is placed on disturbances of wavelength larger than the blade spacing in the autocorrelation analysis. The autocorrelation coefficient of the pressure fluctuation is proposed as a quantitative precursor scale of rotating stall in the vaneless diffuser in the present paper