Transient pressure–vortex coupling mechanisms in a bidirectional tubular pump system with multi-stage straight guide vanes

Bidirectional tubular pump systems (BTPS) are pivotal in coastal low-head pumping applications, addressing simultaneous irrigation and drainage needs. However, conventional straight guide vanes, commonly employed for rectification, exhibit limited hydraulic efficiency compared to curved guide vanes. This study combines computational fluid dynamics simulations and experimental validation to investigate a novel multi-stage straight guide vane arrangement within a BTPS. This study defines the dimensionless guide vane interval (σ) and establishes seven distinct values (σ = 0, 0.11, 0.25, 0.43, 0.67, 1, and 1.5). Through detailed performance and flow-field analyses, the optimal configuration is identified as σ = 0.25. Transient numerical simulations under forward and reverse operating conditions elucidate the transient evolution characteristics of vortex structures, multi-scale vortex interaction mechanisms, and spatiotemporal transport dynamics of the vorticity field within a single blade passing period. Employing continuous wavelet transform and wavelet coherence, the study deeply explores the coupling dynamics between pressure pulsations and vortex structures across multiple temporal and spectral scales. The results indicate enhanced hydraulic performance with multi-stage guide vanes, specifically at σ = 0.25. Prominent recirculation zones and periodic vortex shedding phenomena are observed near the guide vane suction surfaces, synchronized with blade passing frequencies (BPF). The strongest coherence between pressure pulsations and vortex dynamics occurs predominantly at BPF and its harmonics, illustrating intricate feedback mechanisms including pressure-induced vortex formation and vortex collapse-induced pressure fluctuations. The validated findings provide comprehensive insights into the complex fluid dynamics of BTPS and facilitate advanced design guidelines for optimal multi-stage guide vane configurations.