Time-Frequency Characterization of a Rotating Multi-Lobes Pressure Fluctuation in a Centrifugal Vaned Pump

This paper presents experimental investigations of the unsteady phenomena developing in a centrifugal vaned pump. Miniaturized pressure transducers were mounted flushed with the walls on one diffuser blade, in the inlet duct and at the impeller discharge, at different radial and circumferential positions. The analysis was carried out at several flow rates and at two different impeller rotation velocities. The influence of the operating conditions, the presence of diffuser blades on the existence, and the characteristics of the unsteady phenomena were studied. Linear spectral analysis techniques were applied both in frequency and in the time-frequency domains in order to define the pressure signals spectral content and its evolution in time. Moreover, the possible presence of mechanisms of non-linear interaction between pressure pulsations was studied applying functions of the high-order spectral analysis so as to discriminate between fundamental frequency and coupled pulsations due to the interac-tion between the phenomena. The existence of a rotating multi-lobes pressure structure at the impeller discharge, having fluid-dynamical origin, was demonstrated. This instability was verified to propagate both inside and downstream the impeller.