Analysis of multi-field cavitation structure and dynamic mode decomposition based on a separated venturi cavitation generator

Abstract

Cavitation is generated due to the reduction of fluid pressure, which will cause instability and erosion inside the pipeline, valve or pump etc. In this paper, based on the improved venturi cavitation generator, the cavitation under several different flow conditions is studied, and a high-speed camera is used to capture the dynamic process of cavitation at the venturi throat. The flow field simulation data have been analysed using the dynamic mode decomposition method, and the coherent structures of sheet cavitation, transition zone cavitation, and cloud cavitation and their displacements with cycle time have been investigated. The periodic variation of cavitation is analysed using a combination of experimental and numerical simulations, and the state of cavitation in the flow field is investigated in detail using data-driven tools. The results show that periodic changes in the cavitation structure can be observed intuitively through the improved venturi generator and agrees well with the results of simulation. Cavitation intensity is continuously enhanced with the increase of inlet velocity. At flow velocity of 4.68 m/s, the cavitation is manifested as a piecewise cavitation that can only be observed at the throat position, since then the length of the cavitation cloud continues to increase, finally the detachment of a bubble cloud and localized vortex cavitation are observed at velocity of 6.08 m/s. The frequency and growth characteristics of individual flow modes can be accurately captured using the dynamic modal decomposition of the flow field.