Coherence analysis to detect unsteady rotating stall phenomenon based on pressure pulsation signals of a centrifugal pump

Abstract

Rotating stall, one of the intense unsteady flow phenomena, is detrimental to the stable operation of the pump. To investigate rotating stall characteristics in a centrifugal pump, pressure signals are conducted based on the coherence analysis, meanwhile the unsteady evolution process of the stall structure is also depicted in detail. Results show that unsteady pressure signals are significantly affected by rotating stall characterized by the increased pulsation amplitude and low frequency components generated in the pressure spectrum. The point at θ = 18° shows strong coherence characteristics with the other points. According to the coherence results, it is found that at the stall conditions 0.09ФN and 0.06ФN, the same stall frequency at 0.25fn could be captured. However the typical frequency at the stall condition 0.2ФN could not be identified. By using the numerical simulation method, the alternative blocked and unblocked processes caused by the stall cell in the impeller are obtained, and the same stall frequency at 0.25fn is observed for the pump working at 0.2ФN. So, it is concluded that for the stall frequency of the current model pump, they keep unchanged at different stall conditions. Finally, we believe that the current method could capture the rotating stall characteristics, which could be extended to the other fluid machineries.