Evolution of Wake Vortices and Energy Characteristics of Mixed-flow Pumps Under Stall Conditions

Abstract

Unsteady wake dynamics and associated energy dissipation mechanisms in mixed-flow pumps remain critical challenges detrimentally affecting operational stability and efficiency, particularly under off-design operating conditions. This study employs high-fidelity numerical simulations incorporating a modified Wray-Agarwal turbulence model to systematically investigate the spatiotemporal evolution of wake vortex structures and their coupling with energy loss across various flow regimes—ranging from design to deep stall. A multimethod framework integrating Q-criterion-based vortex identification, Dynamic mode decomposition, and entropy production analysis is utilized to characterize flow instabilities and hydraulic losses. Findings indicate that under design conditions, the wake structures exhibit periodicity and dominated by rotor-stator interactions; conversely under stall conditions, large-scale coherent vortices induce significant flow-field disruptions, leading to flow blockage and intensified shear-layer instabilities. The vortex morphology evolves from a stable "T-shaped" structure to a distorted "V-shaped" vortex, ultimately manifesting a multiscale turbulent band during deep stall. Entropy production analysis delineates the tip clearance and mid-span regions as the predominant sites of dissipation, with energy losses increasing by over 80% under deep stall conditions. This work elucidates a quantitative correlation between unsteady vortex dynamics and hydraulic inefficiency, providing a novel diagnostic framework for optimizing pump performance through targeted flow control strategies.