Surging and Stall in a High-Pressure-Ratio Centrifugal Compressor

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In a single-stage high-pressure-ratio centrifugal compressor, the velocity relative to the impeller and to the diffuser usually exceeds the velocity of sound. That is, generation of shock wave is unavoidable, In the present study, variations of pressure are measured in detail using several pressure sensors with high-frequency response mounted on the side wall between circular-cascade vanes where shock waves appear. To propose the primary data for designing of a low-solidity circular cascade diffuser, the relationship between a diffuser stall and a surging, and the structure and unsteadiness of shock waves are discussed. For measurement of the flow between cascade vanes or the impeller inlet, a new PIV system is discussed for its applicability.(1) The frequency-time analysis using a wavelet transform for pressure signals is effective sufficiently to under- stand the incipience time of stall as well as the time change in frequency till the falling in stall. Furthermore, the time- varying … More power spectra or the time-varying rms rules are also effective for the stall analysis.(2) Before the entry to stall, so called a rotating stall was observed at the inducer and the development of stall cell are shown by the history of rms value of pressure fluctuation every one-blade-pitch or by the analysis of blade- passing-frequency component of wavelet transform.(3) Two pressure signals, mounted on the next inter-vanes of cascade diffuser with each other were independent in space as well as in time even at near surge condition. At the beginning of stall, on the other hand, a high spatiotem- poral correlation in pressure fluctuation was observed at the front vaneless zone.(4) A double-pulse YAG-laser PIV system was applied to the flow induced by a rotating disk in a casing and the problems such as accuracy and so on were discussed. It was verified that the present PIV system with the DOP particles, 0.8 mm in diameters, is applicable for the measurement of flow between diffuser cascade vanes and/or at the impeller inlet. Less