Wei Dong

To investigate the transient flow characteristics and flow field hysteresis mechanism within a centrifugal pump during variable speed regulation, this paper selects a double-volute, semi-open impeller centrifugal pump as the research object, through the Pro/E software modeling for centrifugal pump 3-d full port, choosing Renault N-S equation and standard k - ε turbulence model, using CFX software perform numerical simulations process of centrifugal pump up or slow down the transient flow characteristics to carry on the numerical simulation, the evolution law of flow field in centrifugal pump during variable speed adjustment is studied and analyzed. The results demonstrate that the internal pressure, flow velocity, turbulent kinetic energy, and vorticity within the centrifugal pump exhibit distinct transient characteristics during variable speed regulation. During the acceleration phase, as the rotational speed elevates, the internal pressure of the pump increases along with an expanded pressure fluctuation range, the vorticity within the impeller passage increases, the vorticity in the volute chamber decreases, and the fluid velocity and turbulent kinetic energy change obviously in the middle region of the blade working face and the blade tip region. In the process of deceleration, with the decrease of rotational speed, the pressure in the centrifugal pump decreases, the vorticity in the impeller passage decreases, and the vorticity in the volute increases first and then weakens. When t =   0.4 s, pressure on the outlet wall of the volute of the centrifugal pump increases obviously, and the flow velocity and turbulent kinetic energy likewise change obviously in the middle region of the blade working face and the blade tip region. Quantitative comparison further reveals an obvious transient hysteresis effect: under identical rotational speed, the overall pressure and turbulent kinetic energy in deceleration process are higher than those in acceleration process, which provides a new physical understanding of flow discrepancy between two variable-speed modes lacking in previous qualitative researches.

In response to the severe wear of centrifugal pumps, Workbench workflow is utilized to adjust the blade inlet and outlet angles, aiming to reduce the wear of the impeller and volute of the centrifugal pump and optimize the pump’s efficiency and head. Orthogonal experiments are conducted by varying the inlet and outlet angles. The original sample points are expanded and optimized in combination with the support vector machine and grid search. The optimization results indicate that under the condition of spherical particles, the efficiency at the rated operating condition increases by 1.71%, and the head rises by 0.35%. The appropriate eddy currents formed by increasing the impeller inlet angle alleviate the particle deposition phenomenon in the centrifugal pump, resulting in a smoother particle flow. The wear of the centrifugal pump blades decreases from 40.76 × 10⁻⁷ mm to 7.77 × 10⁻⁷ mm. After optimization, the overall entropy generation rate of the volute decreases, while that of the blade suction surface and the impeller outlet area increases. Additionally, through empirical mode decomposition analysis, it is found that the optimized design reduces high–frequency interference and the pulsation amplitude, making the flow field more stable. The frequency distribution also shifts from being dominated by high–frequency components to concentrating energy in the medium- and low-frequency regions.

Variable-speed pump-turbines are central to grid flexibility and accommodating the intermittency of renewable energy sources. Yet the transient flow physics and irreversible energy dissipation during pumping transients remain insufficiently understood. Here, the hydrodynamic instability and dissipation behavior of a variable-speed pump-turbine in pump mode are investigated using multiresolution dynamic mode decomposition and entropy production theory. Across five flow rates from 0.9Qd to 1.1Qd, the results reveal pronounced spectral asymmetry in the runner passages. Low-frequency pulsations of 36.7–62.3 Hz (≈2.0–3.4fn) on the blade suction side are mainly associated with rotational-frequency-related excitation and fluid–blade interaction, whereas the pressure side exhibits broader medium- and high-frequency components up to 293.3 Hz (≈16fn), suggesting stronger flow-separation- and stall-vortex-related hydraulic excitation. Variable-speed regulation modifies entropy production in a flow-dependent manner. Under partial-load conditions, entropy production is reduced to 0.64–0.99 times that of the fixed-speed case because separation-related losses are suppressed. Under overload conditions, it increases to 1.16–1.32 times the fixed-speed level, suggesting enhanced friction-related dissipation. Within the idealized synchronous-regulation framework, acceleration and deceleration exhibit distinct transient flow, force-response, and dissipation characteristics, indicating a hysteresis-like dependence on the regulation path. These findings clarify the coupling among multiscale unsteady flow structures, hydraulic-force response, and irreversible energy dissipation during variable-speed pumping, while noting that practical trajectories may be further affected by hydraulic inertia, guide-vane dynamics, and control delays.

The centrifugal pump is an important component of pumped storage power stations, but the axial force on the impeller significantly affects their stability. Hence, this study focuses on the IS80-65-160 centrifugal pump model and employs Dynamic Mode Decomposition (DMD) to analyze the flow field decomposition of the impeller’s axial forces at three operating points: 1.0nr–1.0Qr, 1.0nr–0.4Qr, and 0.4nr–0.4Qr. The results indicate that DMD can decouple the axial forces on the impeller and extract the temporal mono-frequency coherent structure features and their changes corresponding to the main modes of axial forces, with a nearly zero decay rate and stable periodic vibrations. The first four modes of axial force account for 99.7% of the total modal energy, with the average flow field (mode 0) containing the most flow energy and having the greatest impact on the flow field, The impeller vibrations caused by axial forces mainly occur at the impeller outlet. Modes 1 to 4 of the flow field exhibit similar periodic anti-symmetric coherent structures. At the design speed, the flow field structure is dominated by shaft frequency, but this influence significantly decreases when the speed deviates from the design speed. The findings of this study can help enhance centrifugal pump stability.

The vertical pipeline systems integral to ocean engineering are crucial for the conveyance of fluid media, and thus pivotal in the harnessing of marine resources. This paper describes recent advances in the understanding of such flow dynamics, focusing on the motion of solid particles, vortex formation, and the resultant energy losses. An Eulerian–Lagrangian method is adopted in conjunction with advanced numerical simulations facilitated by Fluent–EDEM software, enabling a detailed examination of energy dissipation in two-phase flows. Utilizing entropy production theory, the entropy production rate within the main flow area is investigated, and its distribution across the pipeline’s cross-section is mapped, thereby providing novel insights into energy efficiency within fluid transport systems. The transient transport of solid particles is investigated, with vortex structures identified using both the Q criterion and vorticity analysis. The dynamic mode decomposition technique is used to obtain a clearer understanding of the distribution and evolution of vortex structures within the pipeline. The findings of this study underscore the respective effectiveness of vorticity analysis in detecting near-wall vortex structures and of the Q criterion in recognizing central flow area vortices. This study contributes to the body of knowledge in fluid dynamics by offering a comprehensive analysis of solid particle motion, vortex formation, and energy loss mechanisms, thereby providing a robust theoretical and technical foundation for the optimized design, operation, and maintenance of pipeline networks in ocean engineering.

This study addresses the hump characteristic issue of mixed-flow pump-turbines under partial load conditions. The response surface methodology and Non-dominated Sorting Genetic Algorithm III (NSGA-III) were adopted for multi-objective optimization of the movable guide vane profile. Numerical simulations were conducted to analyze vortex characteristics in the runner, movable guide vane, volute and stay vane regions, as well as Entropy Production Rate (EPR) distribution in the volute and stay vane before and after optimization. Pressure fluctuations in the vaneless space, movable guide vane and stay vane regions were analyzed via frequency domain method, and impeller axial force variation was studied using Multi-resolution Dynamic Mode Decomposition (MRDMD). Results show that the optimized guide vane profile significantly mitigates hump-region head fluctuation, reduces flow incidence angle, and suppresses flow recirculation and vortex, leading to smoother, more orderly streamlines. High EPR areas in the volute and stay vane were reduced by over 60%. Meanwhile, multi-frequency peaks in the movable guide vane region and non-dominant frequency peaks in the stay vane region were effectively suppressed. Pump-turbine axial force vibration is dominated by rotational frequency and its harmonics, exhibiting medium-low frequency characteristics. This study enhances pump-turbine operational stability and efficiency in the hump region, providing an effective design method and theoretical basis for improving mixed-flow pump-turbine performance under low-load conditions.

Unstable internal flow structures significantly compromise the mechanical reliability of centrifugal pumps. This study elucidates the coupling mechanism between impeller geometry, vortex dynamics, and hydrodynamic forces. A hybrid optimization framework, integrating a neural-network surrogate model with both multi-objective genetic algorithm and non-dominated sorting genetic algorithm III (NSGA-III), was employed to refine the impeller. Comparative analysis reveals that the NSGA-III design offers superior stability, achieving a 31.1% reduction in peak radial force and eliminating axial-force directional reversals, while simultaneously increasing efficiency by 5.4% and reducing shaft power by 6.3%. Crucially, the stabilization mechanism is decoded using multiresolution dynamic mode decomposition (MRDMD) and entropy generation analysis. MRDMD results demonstrate that the optimized geometry attenuates low-frequency unstable modes driven by rotor–stator interaction, shifting spectral energy to stable high-frequency structures. Furthermore, thermodynamic analysis identifies a fundamental shift in dissipation pathways: the suppression of large-scale coherent vortex shedding reduces internal volumetric entropy generation by 63.6%, yielding a flow field stabilized by controlled wall shear layers. These findings provide a physics-based rationale for mitigating flow instabilities through targeted geometric refinement.

In order to reveal the coupling mechanism between hydrodynamic characteristics and entropy production rate under cavitation conditions of mixed flow pumps, this study utilized cross-wavelet transform to analyze the time-frequency domain relationship and coherence between axial force, radial force, and entropy production rate in different regions and cavitation stages. The results indicated a significant negative correlation between the axial and radial forces and the entropy production rate in the impeller region, as compared to the guide vane region. With the development of the cavitation stage, the axial and radial forces exhibited a decreasing trend (the axial force decreased by 25.7% on average and the radial force decreased by 13.1% on average), while the entropy production rate showed an upward trend (the average increase was 30.8%). In the frequency domain analysis, the axial force and radial force in the impeller area were concentrated near the blade frequency (96.67 Hz). In terms of wavelet power spectrum, the high-energy regions of axial force, radial force, and entropy production rate continued to expand in the time range and showed distribution characteristics concentrated near the blade frequency. In terms of wavelet coherence spectrum, the strong coherence regions of axial force and entropy production rate were concentrated at the blade frequency, while the time continuity, overall coherence, and phase consistency were gradually enhanced. The research reflected the strong coupling characteristics of force-energy in blade frequency and its harmonic frequency, which can provide references for improving the operating stability of the mixed-flow pump cavitation process and optimizing blade.