Research on cavitation energy characteristics of mixed flow pump based on entropy production theory and multi-resolution dynamic mode decomposition (MRDMD)

Abstract

Mixed-flow pumps' energy characteristics under critical, severe, and fracture cavitation are investigated in this study using entropy production theory combined with multi-resolution dynamic mode decomposition (MRDMD). The results demonstrate that as cavitation intensifies, the impeller's working capacity progressively declines, leading to a 3 %–15 % reduction in the head. Entropy production analysis shows that compared with non cavitation operation, the weighted average total entropy production of critical cavitation, severe cavitation, and fracture cavitation increased by 7.12 %, 13.62 %, and 26.04 %, respectively. Turbulent dissipation entropy production in the impeller domain constitutes the largest proportion and exhibits an increasing trend, serving as the primary contributor to performance degradation. The impeller's high entropy production zones are localized predominantly at the blade tip clearance and along the suction surface, where energy loss escalates with cavitation severity, resulting in flow channel expansion and blockage. In the guide vane domain, high entropy production zones primarily emerge near the leading and trailing edges, with cavitation-induced flow instability further expanding these regions. Furthermore, MRDMD modal decomposition indicates that the fourth-order mode (corresponding to twice the blade frequency, 193.3 Hz) dominates across all cavitation levels, with its turbulent energy distribution exhibiting pronounced periodic fluctuations at 1/4T(T, The time it takes for the impeller to rotate once). The high turbulent kinetic energy arc-shaped region induced by airfoil cavitation gradually shifts toward the blade trailing edge as cavitation worsens, whereas the turbulent kinetic energy distribution associated with tip leakage vortex (TLV) cavitation exhibits a distinct evolutionary pattern: initial diffusion followed by progressive contraction, accompanied by gradual energy dissipation.