Investigation of the mechanism of unsteady flow induced by cavitation at the tongue of a centrifugal pump based on the proper orthogonal decomposition method

To investigate the unsteady evolution characteristics and mechanism of cavitation at the tongue and its influence on the flow field in a centrifugal pump, numerical calculations were performed to research the occurrence and development of cavitation at the tongue under large flow rate (1.3Qd) conditions. The numerical calculation results were verified by experiments. The proper orthogonal decomposition (POD) method was used to decompose and reconstruct the flow field at the tongue of the centrifugal pump. The relationship between the typical frequency of pressure pulsation and the mainstream structure of the flow field was established. The POD method could accurately extract the coherent structure caused by cavitation and capture the unstable flow structure produced by vortex shedding. Under different available net positive suction head conditions, the first mode was the mainstream structural mode in the original flow field, with low-frequency and single-frequency components. The second, third, and fourth modes were the main oscillation modes of the original flow field and showed the characteristics of high frequency and multiple frequencies. High-order modes could capture the complex flow field structure caused by the change in the large-scale vortex structure induced by the unsteady pulsation of cavitation.