Chuan Wang

There was an error in the original publication

This study numerically investigates the flow characteristics of submerged impinging jets at a standoff distance of H/d = 3. The computational analysis is performed utilizing large eddy simulation (LES) alongside the one-equation Wray-Agarwal and the two-equation SST k-ω and RNG k-ε turbulence models. The current work emphasizes the hydrodynamic structures developing in the unconfined jet region and the variations in flow behavior at the stagnation zone across a range of impact angles (θ ≤ 90°) at Re (Reynolds number) = 23,400. Compared with PIV data, the Wray-Agarwal model accurately predicts the free-jet flow, whereas the RNG k-ε model excels in the wall-jet region. As the impingement angle increases, the pressure distribution calculated by the LES method gradually approaches the experimental results. When the impinging angle θ = 90°, LES has high prediction accuracy in both regions. In general, under the grid scheme used in this study, RNG k-ε can make a more accurate prediction of the average characteristics of the submerged impinging jet flow field.

Box-culvert axial-flow pumps are widely used in flood control, drainage, and water diversion projects; however, when operating under ultra-low or even negative head conditions, they are prone to severe flow separation, backflow, and intensified pressure fluctuations, which threaten operational safety and energy efficiency. To uncover the intrinsic instability mechanisms under these extreme conditions, this study investigates an engineering-scale box-culvert axial-flow pump using a combination of numerical simulations and physical model tests. Three representative operating conditions—design head (1.00Qbep), near-zero head (1.38Qbep), and negative head (1.44Qbep)—are analyzed to examine the internal flow structures, pressure pulsation characteristics, and energy dissipation behavior. By applying the Liutex–Omega vortex identification method, the evolution of flow structures is captured, revealing a continuous transition from locally stable small-scale vortices to large-scale reverse-flow vortices occupying the entire passage. Time-frequency analysis indicates that the pressure pulsations evolve from being dominated by the fourth harmonic of the rotational frequency at the design condition (4.0 fn), to a vortex-shedding-related characteristic frequency at near-zero head (0.75 fn), and finally to a pronounced low-frequency response around 0.25 fn under negative head conditions, reflecting a stepwise amplification of flow instability. Entropy-production analysis demonstrates that the total entropy production under negative head reaches 1.91 times that of the design condition, with turbulent dissipation accounting for more than 77% of the total. The major loss regions expand from the impeller to the guide vanes and outlet conduit, coinciding closely with zones of strong backflow and separation vortices. This study reveals a coupled mechanism characterized by vortex deterioration, pressure pulsation intensification, and enhanced energy dissipation under extreme low-head conditions. The findings provide theoretical guidance for operational optimization, structural improvement, and early warning of instability in pump stations subjected to extreme water-level variations.

Semi-open impeller sewage pumps are widely used for transporting solid-laden fluids due to their anti-clogging properties. However, unlike extensive research on clear water conditions, the specific mechanisms governing pressure instabilities under solid–liquid two-phase flows remain underexplored. This study investigates the unsteady flow field and pulsation characteristics of a Model 80WQ4QG pump using unsteady CFD simulations based on the Standard k−ϵ turbulence model and the Eulerian–Eulerian multiphase model. The effects of flow rate, particle size, and volume fraction were systematically analyzed. Results indicate that the blade-passing frequency (95 Hz) dominates the pressure spectra, with the volute tongue and impeller outlet identified as the most sensitive regions. While increased flow rates weaken fluctuations at the volute tongue, the presence of solid particles significantly amplifies them. Specifically, compared to single-phase flow, the pulsation amplitudes at the volute tongue increased by 68.15% with a 3.0 mm particle size and by 97.73% at a 20% volume fraction. Physically, this amplification is attributed to the intensified momentum exchange between phases and the enhanced turbulent flow disturbances induced by particle inertia at the rotor–stator interface. These findings clarify the particle-induced flow instability mechanisms, offering theoretical guidelines for optimizing pump durability in multiphase environments.

Semi-open impeller sewage pumps are widely used in fields such as municipal wastewater treatment. However, they often face performance degradation and operational instability when conveying solid–liquid two-phase flows containing solid particles. This study aims to systematically elucidate the influence mechanisms of particle diameter (0.5–3.0 mm) and volume fraction (1–20%) on the external characteristics and internal flow field of semi-open impeller sewage pumps, providing a theoretical basis for optimizing their design and operational stability. Using an 80WQ4QG-type sewage pump as the research subject, this study employed a combination of numerical simulation and experimental research. The standard k-ε turbulence model coupled with the Discrete Phase (Particle) approach was adopted for multi-condition solid–liquid two-phase flow simulations. Furthermore, two-way analysis of variance (two-way ANOVA) was utilized to quantify the main effects and interaction effects of the parameters. The results indicate that the pump head and efficiency generally exhibit a decreasing trend with increasing particle diameter or volume fraction, with particle diameter exerting a more pronounced effect (p < 0.01). When the particle diameter increased to 3.0 mm, the head decreased by 5.66%; when the volume fraction rose to 20%, the head decreased by 4.17%. It is noteworthy that the combination of a 0.5 mm particle diameter and a 20% volume fraction resulted in an abnormal increase in head, suggesting a possible flow pattern optimization under specific conditions. Analysis of the internal flow field reveals that coarse particles (≥1.5 mm) intensify the pressure gradient disparity between the front and rear shroud cavities of the impeller, thereby increasing the axial thrust. A high volume fraction (≥10%) promotes pronounced flow separation in the volute tongue region and exacerbates the risk of localized erosion at the outlet.

This study employs an orthogonal test design method, integrating numerical simulation with experimental validation, to investigate the multifactor coupling effects of jetting time (tj), truncation time (t0), Reynolds number (Re), and impact distance (H/D) on the morphology of sandspits formed by submerged jet impingement on a sand bed. The depth (dep) and width (wid) of the sandspit serve as quantitative indicators for analyzing each parameter's main effects and interactions. Simulation reliability is affirmed through grid independence verification and comparison with the experimental data, showing a maximum error under 5%. Results reveal that the sandspit morphology is primarily influenced by Re, followed by tj, H/D, and t0. Interactions among these factors are negligible. For maximizing dep, the optimal parameters are Re = 39920, tj = 1.0 s, H/D = 2, and t0 = 0 s, which results in a 4% increase in dep relative to the original scheme. To maximize wid, the ideal combination is Re = 39920, tj = 1.0 s, H/D = 10, and t0 = 0 s, which results in a 25% increase in wid. Comparing both optimal combinations indicates that prioritizing wid is preferable; this choice leads to a 25% rise in wid and a corresponding 23% boost in dep compared to the initial scheme. The results offer theoretical foundation as well as a parameter optimization framework aimed at enhancing the scouring of submarine pipelines and cables in the context of marine engineering.

Turbomachinery optimization is one of the most important research topics in the field of energy conversion. The velocity moment method is widely recognized for its innovative approach and high computational efficiency. However, previous studies typically assumed a constant velocity moment distribution at the impeller outlet to satisfy the constraint of constant Euler head, which restricted the optimization potential. In this study, a new full-velocity moment method was developed by parameterizing the velocity moments at the impeller outlet using the continuity, energy, and radial balance equations, building upon the traditional velocity moment method. On this basis, parameterized optimization of a mixed-flow pump impeller was conducted through coupling parameter analysis, surrogate model, and optimization algorithm. The performance of the optimized impeller was then experimentally validated. The results indicate that the velocity moment distribution at the impeller outlet significantly impacts the performance of the mixed-flow pump. The weighted efficiency of the optimized model was improved by 3.24% compared to the original model. Specifically, the efficiency at 0.8Qdes, 1.0Qdes, and 1.2Qdes increased by 1.36%, 3.84%, and 5.86%, respectively. The internal flow analysis reveals that increasing the velocity moment at the hub helps prevent boundary layer detachment caused by low-momentum fluid accumulation.

In marine gas turbines, surface roughness on both rotating and stationary disk surfaces can markedly alter flow structures within the rotor–stator cavity, leading to energy losses that remain poorly quantified in the literature. This study presents the first systematic computational fluid dynamics investigation of centripetal through-flow rotor–stator cavities subject to rotor roughness (RR), stator roughness (RS), and combined rotor–stator roughness (RRS) across six rotational speeds (n = 1000–4000 rpm) and a broad roughness range (equivalent surface roughness ks = 0–76.81 μm). Numerical simulations are rigorously validated against bench-scale measurements, ensuring high fidelity of the predicted flow fields and performance metrics. Our results demonstrate that rotor roughness dominantly amplifies boundary-layer disturbances, expands the core vortex region, and induces local vortical structures, whereas stator roughness exerts a secondary influence. Under RRS conditions, cavity performance trends align closely with the RR case. Quantitatively, rotor torque coefficient increases by up to 35% and axial thrust coefficient by up to 18% at ks = 76.81 μm. Finally, we derive and validate empirical correlations incorporating roughness terms for rapid estimation of torque and thrust variations in engineering practice. This work provides actionable insights and practical tools for predicting and mitigating performance penalties due to disk surface roughness in marine gas turbine rotor–stator cavities.

Due to the high safety, low cost, and environmental friendliness, water jet cleaning has become an ideal dredging method for rivers and reservoirs dredging. To accurately investigate the impact of impingement height on the flow characteristics near the impingement wall, this study, in conjunction with comparisons to experimental measurements, selected the RNG (Renormalization Group) k-ε turbulence model and LES (Large Eddy Simulation) method to analyze the time-averaged and transient flow fields of submerged impinging jets with impingement angles θ = 90°, Re (Reynolds number) = 35 100, and various impingement heights H/d = 1, 2, 3, 4, 6, 8. The research reveals that: (1) The axial and radial velocities near the wall depend on the impingement height; the wall blockage effect is confined to within 0.75d, and the jet completes the transition from axial to radial flow at about x/d = 1.8. (2) In the range of 1d from the jet axis, the impingement height significantly affects the distribution of turbulent kinetic energy k/Uj2. (3) The impingement height influences the diffusion of turbulence in the near-wall area; the higher the impingement height, the more fully the shear layer diffuses radially, finally, the jet shear layer completes its inward penetration while the impingement height reaches H/d = 6.