Analysis of two-phase flow in cavitation condition of pump-turbine based on dynamic mode decomposition method in turbine mode

Cavitation is an inevitable and important problem in the design, manufacture and operation of pump-turbine. The research on cavitation of pump-turbine is mainly focused in the pump mode, but the cavitation characteristics of turbine mode are also very important. Traditional research methods are unable to dig a large amount of research data in cavitation flow. Therefore, the dynamic mode decomposition (DMD) method is used in this study to investigate the incipient cavitation and critical cavitation of a model pump-turbine. The results show that the DMD method can accurately extract the characteristics of the runner in pump mode under cavitation conditions. The development of cavitation makes the mode decomposition of the two-phase flow field and the reconstruction of the low order modes significantly different. DMD method is more suitable for signals with clear frequency and simple mean value and pulsation. The development of cavitation makes the reconstruction of low order modes change obviously, from the inception cavitation condition of first waveform reconstruction and then mean-value reconstruction to the critical cavitation condition of first mean-value reconstruction and then waveform reconstruction. It provides a new research idea for cavitation research of pump-turbine. • The characteristics of pump-turbine in turbine mode under cavitation condition are extracted by DMD method. • The influence of cavitation development on the effect of DMD mode decomposition method is clarified. • The applicability of DMD method to different cavitation flow field signals is clarified.