Fujun Wang

In pumping station design, the pump installation elevation is usually determined based on the required net positive suction head under clear-water conditions, NPSHr, together with a prescribed safety margin. However, when sediment is present in the conveyed water, pumps that would not cavitate under clear-water conditions may experience cavitation, while pumps with only slight cavitation in clear water may develop severe cavitation. To address this issue, this study proposes a pump cavitation risk assessment model for sediment-laden pumping stations, based on previously established relationships between cavitation inception pressure, cavitation boiling pressure, and the characteristic parameters of sediment-laden water. Using CFD analysis, the sediment-induced variation in pump cavitation risk is evaluated from two perspectives. First, for a given pump suction height, the cavitation development under clear-water and sediment-laden-water conditions is compared, demonstrating a consistently larger vapor-cavity volume fraction and more rapid cavitation development in sediment-laden water at the same flow rate and suction height. Second, the sediment-induced relative changes in critical net positive suction head, NPSHc, and inception net positive suction head, NPSHi, are quantified. Under the investigated sediment-laden-water conditions, NPSHc and NPSHi increase by up to ∼16.0% and 17.8%, respectively, relative to the corresponding clear-water values over the investigated flow-rate range. These results indicate that more stringent cavitation-prevention measures are required for pumping stations conveying sediment-laden water. The findings provide engineering guidance for the design of pumping stations along sediment-laden rivers and for the safe operation of pump units.

Pumping stations serve as critical hydraulic infrastructure for water conveyance and irrigation. Sediment deposition in forebays can deteriorate intake flow conditions, increase hydraulic losses, reduce pumping efficiency, and consequently impair the long-term operational performance of pumping systems. To accurately predict sediment deposition in complex three-dimensional flow fields, we developed a dynamics-driven boundary-responsive numerical model that integrates sediment particle dynamics with real-time bed evolution. This model adopts the near-bed vertical velocity of sediment particles as the deposition discrimination criterion and dynamically updates bed topography via a mass-conservation-based boundary response strategy. The proposed method was validated against open-channel experimental data. The simulated flow structures, deposition patterns, and temporal variations in deposition thickness agreed well with the measurements, with average deviations below 4%. Compared with conventional static-boundary numerical methods, the proposed model reproduces the coupled evolution of sediment transport, flow redistribution, and bed deformation with higher fidelity. The developed framework provides an effective numerical tool for sediment deposition prediction and offers practical support for hydraulic structure optimization, maintenance scheduling, and energy-efficient operation of pumping stations with sediment-laden flow.

With the large-scale development of renewable energy such as wind, solar and ocean energy, the demand for energy storage is more urgent. Pumped hydro energy storage (PHES) is one of the fundamental solutions to the problem of intermittent supply of renewable energy. The large-capacity/low-head pumped hydro energy storage (LL-PHES) system with the use of tubular pump turbine is a beneficial extension of traditional PHES systems owing to large flow rate and cheaper civil structures. However, the continuous competition between the “static water pressure difference caused by gravity” and the “pressure increase caused by accelerated impeller rotation” leads to prominent instability in the start-up process of the LL-PHES system under pump conditions. An explicit coupling algorithm is proposed for analyzing the transient characteristics in the start-up process of the LL-PHES system under pump conditions. This algorithm is based on the idea of dimensional transformation, and performs 3D flow calculations and 2D rigid body dynamics equation solution in the pump domain and the flap gate domain, respectively. This algorithm avoids the problems of high computational cost and poor convergence that exist in existing fully three-dimensional coupling algorithms and ensures the efficiency of transient hydraulic characteristic calculation. A comprehensive analysis of the transient characteristics of the LL-PHES system during pump start-up process is conducted using the proposed new algorithm. The entire process of the increase in rotational speed, valve opening, flow rate, and the continuous evolution of blade surface pressure during the start-up process is quantitatively described. The amplitude and spectral characteristics of the alternating pressure on multiple blades are clarified. The evolution law of blade load during the stage of severe pressure fluctuations during the start-up process is explained. The load distribution characteristics of “high in the leading and trailing edge areas and low in the middle” in the blade stream direction is presented. The research results have a direct guiding role in improving the hydraulic design and enhancing the operational stability of LL-PHES systems.

This study aims to elucidate the rotor–stator interaction (RSI) mechanism in a centrifugal pump by employing high-fidelity stress-blended eddy simulation (SBES) turbulence modeling combined with reduced-order techniques [dynamic mode decomposition (DMD) and proper orthogonal decomposition (POD)]. The core objective extends beyond confirming the dominant frequency characteristics, to quantifying the energy hierarchy of RSI-induced flow and resolving the energy cascade in a coupled space–time–frequency domain. The present work investigates the RSI in a pump based on the European Research Community on Flow, Turbulence and Combustion standard through three-dimensional, unsteady computational fluid dynamics simulations. Initially, the SBES and scale-adaptive simulation turbulence models were compared. It was observed that the SBES model had good predictive accuracy compared to the experimental data for the pressure coefficient, velocity profiles, and pressure fluctuations in the vaneless region. Further transient study using SBES showed that blade passing frequency (fBPF) and its second harmonic are the predominant frequencies in terms of pressure pulsations. Also, the energy variability of frequencies was distinct across the flow path. Reduced-order analysis showed low-dimensional features of the flow. DMD's isolation of the first four dominant modes, corresponding to fBPF and its harmonics, was successful, with their spatial structures visualizing the large-scale periodic wakes and associated small-scale vortex shedding from RSI. A reconstruction based only on the first 5 DMD modes is able to capture the essential dynamics of the actual flow field in the study. POD analysis confirmed previous results for the energetic behavior. It clearly indicates that the first four modes contain more than 66% of the total energy. Moreover, the corresponding spectra of modal coefficients perfectly align with the DMD frequencies. This synergy of results confirms that periodic wakes from RSI are the primary energy-driving mechanism. This work seeks to reveal how the transient vortex structures influence pressure and Reynolds stress fluctuations, thereby providing physical insights beyond conventional spectral analysis for flow-induced vibration and noise control, and offers a basis for optimizing fluid machinery design.

Large-scale vertical centrifugal pumps are widely used in the water diversion projects in China, and the pumping stations often operate in the river environments with suspended sediments. The problem of impeller wear caused by sediment-laden flow is very prominent, seriously affecting the safety, stability, and efficient operation of the units. The sediment-laden flows in large-scale vertical centrifugal pumps exhibit the features of high volumetric concentration and small particle size (huge number of particles per unit volume). Under these service conditions, the characteristics and mechanisms of impeller wear are still not fully understood. This study takes a vertical centrifugal pump model as an example and conducts research in combination with hydraulic model experiments. First, a new Eulerian–Eulerian two-phase flow model suitable for high concentration and fine particle water–sand two-phase flows in centrifugal pumps is established. Second, a new wear model applicable to the base material of the impeller wall of a centrifugal pump is calibrated. Third, the water–sand two-phase flows in the vertical centrifugal pump under the conditions of different fine particle sizes are simulated, and the characteristics of erosion rate, particle impact velocity, and particle impact angle in the impeller are quantified. Moreover, based on the dynamic balance relationship of the relative motions, the mechanism behind the impeller wear under this condition is revealed, which originates from the special balance between the potential rothalpy gradient, the Coriolis force, and the drag force. In summary, the above results can provide valuable guidance for the anti-wear protection of large-scale vertical centrifugal pumps.

Water-sediment swirling flow is ubiquitous in rotating machinery. The centrifugal field drives the liquid outward and generates intense azimuthal shear, which in turn enhances the relative motion between water and sediment. The influence of the rotational effect on the velocity distribution of the two phases, particularly the relationship between vortex intensity and interphase slip velocity, has not yet been fully clarified. Based on PIV (particle image velocimetry) experiments, measurements were conducted on a dilute water-sediment two-phase flow with a magnetic stirrer rotating at 400–800 r/min and sediment particles ranging in size from 20 to 150 μm. The experimental results indicate that in the water-sediment swirling flow system, under the same rotational speed and particle size, the circumferential distribution of the time-averaged velocity of the water-sediment two-phase flow exhibits strong uniformity across the azimuth, while the radial distribution shows a trend of first increasing and then decreasing with increasing r/R. Overall, the slip velocity decreases with increasing r/R, and larger values typically appear in the regions with a larger rotation-rate tensor magnitude or higher fluid velocity. The peak time-averaged velocity and St (Stokes number) of the two phases increase with increasing rotational speed and particle size, and the turbulence intensity of the particle phase is higher than that of the liquid phase. Furthermore, there is a significant positive correlation between ‖Ω‖F2, which characterizes the vortex strength, and the relative slip velocity, indicating that greater vortex strength tends to enhance the relative motion between particles and the fluid.

This paper aims to analyze the leading edge cavitation of a double-suction centrifugal pump, focusing on its periodic evolution process and unsteady characteristics. The calculation of external characteristics and the simulation of the leading edge cavitation in the double-suction centrifugal pump were performed based on the turbulent viscosity correction model. The cavitation was studied under three working conditions (0.5, 0.9, and 1.2 times the design flow rate). The position and structural characteristics of the leading edge cavitation were identified. The instability phenomenon and vortex motion in the impeller passage caused by cavitation were analyzed. The results indicate the inlet flow of the impeller and the pressure distribution on the blade surface are the primary factors influencing the characteristics of the leading edge cavitation. The inlet flow of the impeller determines the position of the leading edge cavitation, while the pressure distribution on the blade surface dictates the specific shape and structure of the cavitation. Throughout the development cycle of cavitation, the position of the flow instability region within the impeller shifts from the off-flow area of the leading edge to the tail of the cavitation region.