Development and application of the entropy production diagnostic model to the cavitation flow of a pump-turbine in pump mode

Abstract

A novel mathematical model, entropy production diagnostic model (EPDM) with phase transition (EPDMS), was developed, which is practical to analyze the irreversible loss for cavitation flow in hydraulic machinery by including mass transfer and slip velocity. To model the corresponding flow, two-fluid model with main interphase forces was employed. Compared with the EPDM in homogeneous model, two extra contributions, diffusion and interface entropy production (DifE, IntE), are added in EPDMS. Then, EPDMS was validated by experiments of a pump-turbine in pump mode at three off-design conditions. The improved numerical model is more accurate in capturing the typical cavitation points, while the original one is obviously lower due to poor consideration of phase interaction. Therefore, the loss predicted by EPDMS is more rational. A detailed comparison among four overlapping items of EPDM and EPDMS was performed. It shows that these items merely interpret the accumulative effect of cavitation on the flow, while as a key part of EPDMS, IntE is closely related to the evolution of cavitation. Moreover, low-frequency excitation that caused by cavitation-induced vortex is captured by the probe at the edge of the cavity, which is consistent with the frequency-domain characteristics of IntE instead of other items.