Pumped hydro storage is one of the most sustainable energy storage technologies, accounting for over 90% of global energy storage capacity. It faces challenges related to fish injury and mortality similar to those encountered by conventional pumping stations. In this study, the bending profile of the so-called fish-friendly-twisted blade, recognized as the key geometric parameter affecting fish safety, is mathematically characterized using a novel power function. The systematic assessment of the twisted blades with varying exponential factors is performed, focusing on flow distortion, energy loss and operational reliability. Results indicate that as the exponent decreases, the blade leading edge tends to be more inclined toward the fish trajectory near the blade tip, resulting in a significant reduction in strike velocity and improved fish friendliness. Compared to blade morphologies with exponents of 4, 2, 1 and 0.5, the configuration with an index of 0.25 produces a more confined vortical flow in both size and intensity, and achieves a higher level of flow uniformity. This bending profile consequently mitigates flow-induced instabilities, including radial and axial forces as well as blade loading, and decreases the vortex-induced energy losses, particularly those caused by the leading edge hub vortex and the tip leakage vortex. The outcomes of this research offer comprehensive guidance for the design and application of fish-friendly blades in pumps and turbines, promoting the development of eco-friendly hydraulic machinery.

The rapid development of offshore wind and marine renewable energy systems has intensified the demand for large-scale coastal pumped-storage facilities to ensure grid stability. Vertical intake systems deployed in such marine environments are highly susceptible to air-core vortex (ACV) formation, which may compromise hydraulic safety and reduce energy conversion efficiency. To elucidate ACV formation and suppression under vertical intake conditions, high-speed visualization experiments combined with three-dimensional multiphase simulations were conducted. Results show that at low Submergence ratios, ACVs exhibit pronounced unsteadiness, with vortex cores undergoing large-scale migration and interacting with bottom-attached vortices, thereby inducing bottom cavity structures. At higher submergence ratios, the ACVs develop a slender core structure with sustained air-column continuity and remain confined to the rear-wall corner region. Mechanistic analysis indicates that ACV inception originates from strong vertical vorticity generated by flow separation in the pipe wake, while vorticity tilting in the tangential and radial directions near the corner regions governs subsequent ACV intensification. As the ACV migrates toward the wall, wall-induced shear and the entrainment of counter-rotating vortices substantially attenuate the vorticity, resulting in rapid decay. Based on these insights, two suppression strategies are proposed and experimentally validated, providing guidance for ACV mitigation in vertical intake 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.

The waterjet pump with inlet guide vanes (IGVs) are widely used in propulsion systems of modern underwater vehicles. Understanding its complicated hydrodynamic characteristics is beneficial to improve the comprehensive performance. In this study, numerical simulations and experimental tests are carried out concurrently to investigate the flow field, energy losses and excitation characteristics of the waterjet pump. The results show that there is an obvious rotor-stator interaction between the IGVs wake and impeller blades, which leads to the thrust spectrum of the impeller is jointly dominated by the line spectrums located at the blade passing frequencies of impeller fBPF and IGVs fs. The negative pre-swirl flow induced by the IGVs could effectively offset the circumferential velocity at the impeller outlet, and this offset degree is closely related to the flowrate conditions. The quantification and visualization of the energy loss based on the diagnostic model derived from the mean kinetic energy equation shows that the impeller tip leakage flow and induced leakage vortex are the main sources for energy loss generation. The tip leakage flow also induces notable pressure pulsations dominated by the fBPF. Under part-loading condition, the deteriorating unsteady flow within the waterjet pump leads to an increase in energy loss, and correlatively attributes obvious broadband features to the spectrums of pressure pulsation and unsteady forces as well as increased low frequency amplitudes.

The two-stage double suction centrifugal pump (TSDSCP), a pivotal component in pumped-storage hydropower systems, is widely employed across various sustainable energy sectors. Its operational stability is paramount, as it significantly affects the system's energy conversion efficiency and ensures the long-term reliable operation essential for the viability of these green energy solutions. The study specifically focused on the impact of the staggered arrangement of double suction impellers on the pressure pulsation within TSDSCP. Two impeller configurations, symmetrical and staggered, were experimentally established to evaluate the pressure pulsation behavior under different staggered conditions. The staggered impeller configuration was found to slightly increase efficiency by 0.04 % under design working conditions, marginally reducing the head by 0.6 m, and decreasing power consumption by 1.53 kW. These outcomes indicate that the impeller configurations have a relatively small impact on energy conversion efficiency and head. Notably, the amplitude of pressure pulsations was observed to be lower in the staggered impeller setup across the suction, vane, and pressure chambers when compared to the symmetrical arrangement. Specifically, at the design flow condition, the dominant frequency amplitude (DFA) in the suction chamber was reduced by 70 %, and under low flow conditions, a 39 % decrease was noted. A significant decrease in pressure pulsation was observed at the blade exit, especially at 0.6Q operation, where the DFA was diminished by 35.3 %. Employing the Stress-Blended Eddy Simulation (SBES) model for numerical calculations, further analysis of the wake-jet structure and the flow distribution at the entrance of the volute indicated that the staggered impeller enhances the uniformity of flow discharge and mitigates pressure pulsations caused by rotor-stator interactions. When the flow rate is low, the spinning vortex intensity in the staggered impeller's volute is lower, which in turn causes the pressure pulsations to be even less. Staggered impeller configuration greatly improves pump flow stability, leading to more stable operation, according to experimental and numerical studies.

A kind of flow distortion is found in the design and application of the so-called tubular-flow fish-friendly pump, which possesses a highly twisted blade leading edge for reducing fish damage. It is named as leading edge hub vortex (LEHV) and has a closer relationship with flow instability and energy loss compared to the well-known tip leakage vortex (TLV). Numerical and experimental investigations are implemented in a typical tubular-flow fish-friendly pump, in terms of the evolution of LEHV in size and strength, as well as the vortex-induced low pressure and energy loss. The evolution of LEHV is divided into four stages, namely the inception, radial development, alternation of rotation direction, and vortex detachment. The vortex dynamics exhibit distinct periodicity with varying intensity and position due to flow fluctuation in the rotating pump. Further results on vortex-induced instability reveal that the volume with low pressure near the hub is much larger than that near the tip under multiple flow conditions, indicating that the cavitation inception is more likely to occur near the hub, which seems different from the common sense that cavitation appears initially at the blade tip. Moreover, it is found that the LEHV plays a more significant role in causing energy loss compared to TLV at low flow conditions, and the wake vortex formed by the interaction between LEHV and wake flow causes considerable energy loss near the impeller exit. This study will provide scientific guidance and optimization strategies for the design of a fish-friendly pump to improve hydraulic performance and stability.

Summary Gas-liquid two-phase mixed-flow transportation is a critical factor that reduces the hydraulic performance and stability of electrical submersible pumps (ESPs). Therefore, this study proposed semi-open-type multistage ESPs to improve their ability to handle gas-liquid mixed-flow transportation. The ESPs’ performance was predicted using a nonhomogeneous Euler-Euler two-fluid model combined with the multiple-size-group (MUSIG) model at various inlet gas volume fraction (IGVF) conditions. The accuracy of the simulation was verified with the experimental results. The results explored the influence of different tip clearance sizes on the energy characteristics and internal unstable flow of ESPs. The results show that using semi-open impellers improved the working performance. When IGVF = 5%, the scheme with the tip clearance of 0.2 mm had certain advantages. When IGVF = 10%, the scheme’s benefit with tip clearance of 0.4 mm was more prominent. The semi-open impellers significantly improved the flow state in the first-stage impeller channels and reduced the interstage differences. The energy loss caused by bubbly coalescence was decreased due to the enhanced turbulence intensity caused by tip leakage flow. The leading cause of energy loss in the current high turbulent kinetic energy (TKE) area was the rolling-up effect of the tip leakage flow. Under different IGVF conditions, the bubbles occurred in various degrees of coalescence and breakup. The theoretical basis and optimization direction are provided to improve the gas-liquid mixed-flow transportation performance of ESPs.

The phenomenon of rotating stall in centrifugal pumps is closely associated with the evolution of the blade boundary layer. Aiming to accurately predict the characteristics of the boundary layer, this study investigates the phenomenon of rotating stall in centrifugal pump impellers using the gamma (γ) transition model. The accuracy of the numerical simulation was confirmed by comparing its conclusions with the results of the testing. In calculations considering transition characteristics, the distribution of low-pressure areas inside the impeller is relatively discontinuous, while the pressure distribution is more uniform. However, in calculations without considering transition, the low-pressure regions in neighboring flow channels exhibit a tendency to be interconnected, resulting in a more variable pressure distribution, and the pressure contour at the outlet is closer to parallel. The dynamic characteristics of the centrifugal pump impeller rotating stall were obtained through the dynamic mode decomposition method, including the frequency, structure, and dynamic evolution process of the stall vortex. Through modal reconstruction, it was discovered that the impeller's rotation causes the stall vortex to undergo periodic fluctuations. The stall vortex is not stationary but moves synchronously with the rotation of the blades. At different time points, the stall vortex exhibits periodic changes. At the blade suction entrance, the stall vortex initially appears. Subsequently, multiple vortex structures resulted in channel blockage. After a period of development, the excess vortex structures merge to generate a typical “8” shaped vortex structure and move toward the exit. Finally, the exit stall vortex disappears, and a new vortex structure is generated at the inlet of the blade suction surface.

Model predictive control (MPC) is used to manage water systems, and its performance depends on the (internal or control-oriented) model it is based on. Several models for the hydraulics of open water systems are presented in literature and used in applications, but their performance has not yet been investigated systematically, and no guideline exists on which model to select for a certain channel. The aim of this research is to present a guideline for model choice based on the geometry of the channel and the flow conditions. The guideline is developed by first categorizing the channels into four types, followed by performing time-domain, frequency domain, and closed-loop tests for all models and channel types. The evaluation of the tests shows that for short and wave-dominated channels, the Muskingum, Integrator Delay, and Integrator Delay Zero models perform the best, while for longer channels the linear inertial model is the most suitable. Finally, a decision-tree is presented how to choose the model. Lastly, a decision-tree is introduced to aid in the selection of the most appropriate model. Irrigation channels, drainage channels, reservoirs are crucial for us and they have to be managed. Water in them should be distributed safely, on time and satisfying all necessities, for example, irrigation, fishing, flood protection. This is achieved by controlling these water systems with hydraulic structures such as gates, weirs and pumps. One way of controlling these structures is so called model predictive control (MPC), a technique which is based on a simple model of the water channel and with the help of mathematical optimization calculates what the hydraulic structures should do, for example, open a sluice gate. There are several different simple models are available for this technique. This article describes a technique how to choose the best simple model for a given open water channel for MPC, based on the geometry and the discharge in the channel-which is easy to be estimated. Therefore it is a straightforward guide of choosing a model for MPC of open channels. Simple models for open water channels for control purposes are compared through open and closed-loop simulation tests and frequency response Open channels are categorized based on their geometry and flow conditions and for each category a model is recommended A guideline is given for internal/surrogate model choice for control purposes

Axial liquid hydrogen pumps, essential for aerospace and energy sectors, offer high efficiency and reliability at extremely low temperatures. The significance of the tip clearance flow of axial liquid hydrogen pumps, in its interaction with the main flow, wall boundary layer, and wake flow, is paramount in determining the overall stability of the system. This study looked into the characteristics of axial liquid hydrogen pumps' tip leakage using numerical modeling methods. Regarding the leakage characteristics of hydrofoils (as a simplified form of pump blade), the predictive capabilities of three turbulence models-Shear Stress Transport (SST) k-omega, StressBlended Eddy Simulation (SBES), and Large Eddy Simulation (LES)-were compared. In terms of predicting the location of downstream tip leakage vortices, both the SBES and LES models align relatively well with experimental data. While the SST k-omega model offers computational efficiency, the SBES model demonstrates higher accuracy in predicting the velocity field near the core of the leakage vortex flow field, combining both efficiency and accuracy advantages. For the research on the pumps, with increasing flow rates, the leaky vortex's strength and effect range gradually decreased, and the vorticity value in the core region also decreased. This shift shows that as the flow rate increases, the leakage vortex becomes more stable. Additionally, the investigation was conducted on the pressure fluctuations on the blade surface. Under design conditions, the pressure fluctuations exhibited periodic changes, with their frequency primarily determined by the rotation frequency of the impeller. By establishing monitoring points on the blade surface, the study found that the amplitude of pressure fluctuations near the leading edge increased with increasing flow rates, whereas decreased at the suction and pressure sides. Under low flow conditions, due to the large amount of leakage and the poor stability of the leakage vortex, the pressure fluctuations on the back of the blade were more significant. This work offers theoretical assistance and technological direction for understanding and predicting the leakage characteristics and blade pressure fluctuations of axial liquid hydrogen pumps.

This work investigates the cavitation and fluid–structure interaction characteristics of a flexible NACA0015 hydrofoil. The simulation incorporates the Zwart–Gerber–Belamri cavitation model and two-way fluid–structure interactions. The detached eddy simulation method is employed to analyze the impact of cavitation and elastic deformation on hydrodynamic performance. The vibrational response and cavitating flow field around the hydrofoil are investigated. The results show that the vibrational mode of the elastic hydrofoil shifts with increasing flow speed. Furthermore, the vertical vibrational displacement of the hydrofoil aligns with the variations in cavitation volume in the flow field. The structural vibrational deformation of an elastic hydrofoil notably affects the evolution of cavitation. Additionally, fluid–structure interaction in the presence of cavitation influences the pattern of vortex shedding wakes in the flow field. The results of this study can serve as a reference for the design of hydrofoils constructed from composite elastic materials.

The inducer is an axial flow pump installed at the inlet of the condensate pump, which is a key equipment in ocean engineering. It enhances the anti-cavitation ability of the condensate pump by pressurizing the incoming flow. This study aims to numerically investigate the thermodynamic effects on cavitation performance and the interaction between cavitation and vortices in an inducer. To better understand the thermodynamic effects, a comparison is conducted and analyzed for the inducer operating under isothermal and non-isothermal conditions. The results show that at smaller cavitation numbers, the thermodynamic effect more significantly restrains cavitation development. This leads to larger cavitation volumes under isothermal conditions compared to non-isothermal conditions, with backflow vortex cavitation occurring earlier in the isothermal state. The Coriolis force contributes the most to vorticity generation, with its range and intensity significantly greater under isothermal conditions.

Hydrofoil shapes are used for the marine turbine blades to capture kinetic energy from water currents effectively. Predicting transitions is a critical concern when studying the hydrofoil boundary layer. This paper analyzed the transitional behavior of the boundary layer in the National Advisory Committee of Aeronautics (NACA) hydrofoil, NACA0009, with a blunt trailing edge using the Algebraic Local-Correlation-based Transition Modeling (Algebraic LCTM) model. First, through sensitivity analysis, the effects of the maximum y+ (the dimensionless distance y to the wall), grid expansion ratio, number of normal and streamlined grids, and timescale on transition prediction were studied. The results indicate that finer y+ value and appropriate grid expansion ratios can improve the accuracy of transition prediction, while the influence of timescale on the prediction results is relatively small within the range of Courant number theory values. Second, further analysis was conducted on the transition prediction performance under different Reynolds numbers. It was found that the model predictions were consistent with experimental values at low Reynolds numbers, but the predicted transition position was advanced at high Reynolds numbers, mainly because of the significant disparity in eddy viscosity coefficients within the free flow field. In the study of leading-edge roughness bands' impact on boundary layer transition for hydrofoil, the introduction of roughness significantly expedited the transition process. The Algebraic LCTM model outperformed the gamma (gamma) transition model, reducing prediction errors by 5-40% for boundary layer parameters and maintaining errors between 0.005 and 4% for wake vortex shedding frequency, as opposed to the gamma model's 0-23%. The results of this study provide a theoretical basis for hydrofoil design.

The flapping vortex dynamics of two flexible plates submerged side-by-side in the wake of a square cylinder are investigated through a two-way fluid–structure interaction (FSI) simulation. The gap between the two plates can stabilize wakes, lengthen vortex formation, elongate vortices, suppress vortex shedding, and decrease hydrodynamic forces. The numerical results indicate that the two flexible plates can exhibit four distinct modes of coupled motion: out-of-phase flapping, in-phase flapping, transition flapping, and decoupled flapping, depending on the gap spacing. Additionally, it is discovered that each of the four coupling modes has a unique pattern of vortex development. The findings of this study should proved valuable in the design of FSI-based piezoelectric energy harvesters utilizing cylinder–plate systems.

Tip leakage vortex (TLV) usually exists at a small tip clearance in axial-flow energy conversion machines, which may induce flow loss, vibration, noise and vortex cavitation. In this work, the double-control-hole (DC hole) at the leading edge of a hydrofoil is used to suppress TLV by inducing a passive jet. The SST-CC model by adding a rotation-curvature correction (CC) term into the original shear stress transport (SST) k-omega and Zwart-GerberBelamri (ZGB) model were applied to investigate the controlling effect under different Reynolds numbers (Re). The results show that TLV is decomposed and new vortices are generated when changing Re. By guiding the high-pressure flow from the pressure side (PS) to the suction side (SS) of hydrofoil vertically, the TLV core pressure is increased and local cavitation is suppressed. When the inflow velocity gradually increases to 7.5 m/s, 10 m/s and 12.5 m/s, the velocity swirl intensity at the TLV core is suppressed by nearly 50%, 36.4% and 28%, respectively, showing a downward trend. Based on the vorticity equation, it is observed that the distribution of TLV vortex bending terms is changed. Also, the vortex bending term and the vortex stretching term are suppressed in specific directions. Further analysis of the suppression mechanism of DC hole indicates that this structure can increase the turbulent kinetic energy of TLV, which destabilizes the flow field. Besides, the velocity circulation in the downstream region of TLV can be reduced, which can suppress the TLV effectively.

In low-head pumped hydroelectric energy storage systems operating in pumping mode, the tip clearance leakage vortex, emerging from the narrow gap between the impeller's outer perimeter and the pump casing, significantly impacts unit efficiency, head, and energy consumption. This paper uses simulations combined with experiments to study how the leakage vortex forms and changes in the pumping mode. Our methodology incorporates the Rigid vortex technique to perform a detailed three-dimensional structural analysis of the leakage vortex and its developmental stages. The findings indicate that the presence of tip leakage flow initiates the formation of a complex vortex structure. This structure comprises primary and secondary vortices, the dynamics of which are significantly influenced by interactions with the main flow. At low flow conditions, we observed that the primary vortex, originating at the head region on the back of the blade, undergoes premature collapse. This collapse is manifested by a shortened core band, diminished stability, and intensified vortex motion, accompanied by an increased angle relative to the blade posterior region. The leakage vortex separation and shedding take place near the entrance of the adjacent blade. Conversely, as the flow rate increases, the main vortex core band extends, leading to enhanced stability. The angle between the core band and the blade back diminishes, resulting in the leakage vortex separation and shedding occurring further along, towards the leading edge of the neighboring blade. This shift in vortex behavior covers a substantial portion of the flow field, impacting the overall efficiency and stability of the units. The results guide stability improvement in low-head pumped storage pumping mode operation.

The tubular pump is a typical water transfer apparatus designed for extremely low heads and large flow rates. It serves as the core equipment in pumping stations situated at lakes, rivers, and canals. An adverse effect on the ecological environment stems from fish injury and mortality primarily caused by blade strikes. The present work combines computational fluid dynamics and the discrete element method to simulate the dynamics of fish passing through a simplified blade, allowing us to establish a safe margin of the strike force to further assess fish damage in a more complex tubular pump system. The results indicated that strikes on fish alter their motion state in terms of direction and magnitude, inducing chaotic movements that heighten the risk of subsequent strikes with downstream components. Fish tend to align their velocities with the surrounding fluid due to flow-induced drag after multiple contacts with solid structures. The knife-shaped leading edge, and particularly the blade tip side, emerged as the primary factor in creating strike damage, and the adoption of a slanted and blunt leading edge can effectively reduce fish damage. In addition, decreasing the shaft speed, increasing the flow rate, and restricting the fish size were identified as measures conducive to fish survival in running pumps. The study further suggested that using fewer but larger pumps operating at lower shaft speeds would contribute to better fish friendliness, which can also ensure a sufficient delivery head and mass flow rate.

In the realm of marine science and engineering, hydrofoils play a pivotal role in the efficiency and performance of marine turbines and water-jet pumps. In this investigation, the boundary layer characteristics of an NACA0009 hydrofoil with a blunt trailing edge are focused on. The effectiveness of both the two-equation gamma theta (γ-Reθt) transition model and the one-equation intermittency (γ) transition model in forecasting boundary layer behavior is evaluated. When considering natural transition, these two models outperform the shear stress transport two-equation (SST k-ω) turbulence model, notably enhancing the accuracy of predicting boundary layer flow distribution for chord-length Reynolds numbers (ReL) below 1.6 × 106. However, as ReL increases, both transition models deviate from experimental values, particularly when ReL is greater than 2 × 106. The results indicate that the laminar separation bubble (LSB) is sensitive to changes in angles of attack (AOA) and ReL, with its formation observed at AOA greater than 2°. The dimensions of the LSB, including the initiation and reattachment points, are found to contract as ReL increases while maintaining a constant AOA. Conversely, an increase in AOA at similar ReL values leads to a reduced size of the LSB. The findings are essential for the design and performance optimization of water-jet pumps, particularly in predicting and flow separation and transition phenomena.

The vertical centrifugal pump is a commonly utilized unit in seawater-pumped storage hydropower plants. The volute, a crucial part of the pump, directly influences the hydraulic characteristics, stability, and efficiency. The effect of single- and double-voluted configurations on a vertical centrifugal pump is studied using the SAS (Scale Adaptive Simulation) turbulence model in this study. The validity of the computation procedure is confirmed when compared to the test results. An investigation into the pressure pulsation and the radial force is carried out. The findings indicate that different volute types do not have appreciable effects on pump efficiency or head, and the variance is less than 2 %. However, the volute design greatly affects the pressure pulsation of the casing. At three typical working conditions (0.6Q, 1.0Q and 1.1Q), the main frequency amplitude at the first tongue of the double volute is reduced by 70 %, 38 % and 40 % compared with the corresponding single volute. At the outlet of the double volute, it is 31 %, 18 %, and 22 % lower when compared to a typical single volute. The type of volute used in the pump influences the pressure distribution as well as the pressure pulsation characteristics. As the double volute adopts the diaphragm structure, its radial impeller force is smaller. When comparing single and double volute pumps, the latter has a smaller radial impeller force. Therefore, it is advised to utilize a vertical centrifugal pump with a double-volute structure. This paper provides valuable insights for selecting units for seawater-pumped storage hydropower plants.