Search Results (398)

Coherent vortices alter flapping-foil energy harvesting, but wake-generated vortex properties and timing are coupled to upstream-body kinematics. We use two-dimensional immersed boundary–lattice Boltzmann simulations of a prescribed heaving–pitching NACA0015 foil at $Re=1100$. An independently prescribed Taylor vortex allows nominal encounter phase, body-fixed offset, diameter, and intensity to be varied at fixed kinematics. Production-grid ${\overline{C}}_P$ is within $0.10\%$ of the fine-grid result; the fine-grid diffusion test gives a maximum full-field velocity $L_2$ error of $0.0690\%$ against the analytical solution over $0\le t^{*}\le 4$. For the reference vortex with a pivot-centered nominal target ($D/c=v_{\theta m}/U_{\infty }=1$), nominal-encounter-aligned mean power coefficients of $0.747$, $0.862$, and $0.987$ occur at ${\psi }_e=0.10$, $0.40$, and $0.60$, respectively, compared with $0.832$ without gusts. These define the power-reducing (PR), near-baseline (NB), and power-enhancing (PE) cases. Within the sampled ranges, diameter is associated mainly with disturbance reach and duration, intensity with loading magnitude, and offset with spatial overlap and interaction timing. Power variations are consistent with the timing of vortex-modified loading relative to prescribed foil motion. In three same-sign, once-per-cycle sequences, the PR–NB–PE ordering persists despite residual-wake interactions, with sustained mean power coefficients of $0.763$, $0.916$, and $0.965$, respectively. Nominal encounter phase and foil placement should be considered jointly for repeatable or predictable vortex passages. Full article

During vacuum induction melting (VIM) of superalloys, oxygen and nitrogen control involves interfacial processes at both the melt free surface and the crucible–melt interface, where melt flow is an important factor affecting reaction kinetics. A coupled electromagnetic and fluid flow model with a deformable free surface was developed and validated for a 3 t industrial VIM furnace with two electromagnetic excitation modes. The melt flow under the Heating and Stirring modes is compared, with particular attention to the role of free-surface deformation, and the effects of input power and filling ratio are further examined. The results show that at an input power of 190 kW and a filling ratio of 85%, the Heating mode produces two counter-rotating vortices separated by a low-velocity mid-region, while the Stirring mode generates a dominant upper vortex covering most of the melt volume with a smaller counter-rotating vortex at the bottom. The Stirring mode achieves approximately 1.3 times the surface velocity, 1.7 times the wall friction velocity, and half the mixing time of the Heating mode. Free-surface deformation significantly affects the predicted flow structure, particularly under the Heating mode. Parametric results further show that input power mainly changes the flow intensity without altering the flow structure under either mode. By contrast, the filling ratio strongly affects the flow structure under the Heating mode, while that under the Stirring mode is largely preserved. These findings provide insight into the melt flow conditions relevant to oxygen and nitrogen removal during VIM processing. Full article

Pump-as-Turbine (PaT) systems represent a cost-effective solution for hydraulic energy recovery in existing water networks and industrial processes. However, the prediction of their performance in turbine mode remains challenging, especially under off-design conditions where unsteady flow structures and internal losses strongly affect the machine efficiency. In this work, transient CFD simulations of a real industrial centrifugal pump operating as a turbine are performed using OpenFOAM and ANSYS CFX and compared with available experimental data. The investigated operating range extends from $0.7Q_{\mathrm{BEP}}$ to $1.3Q_{\mathrm{BEP}}$. A mesh independence analysis is first carried out using the Grid Convergence Index method, leading to the selection of a mid-size computational mesh as a compromise between accuracy and computational cost. The transient OpenFOAM results show close agreement with the ANSYS CFX predictions over the complete operating range. Both numerical frameworks reproduce the experimental hydraulic-efficiency trend and the location of the BEP, while systematic deviations in hydraulic head and mechanical power are mainly attributed to the geometrical and physical simplifications adopted in the common computational model. The local pressure coefficient monitored at the tongue region shows that both the mean pressure level and the fluctuation amplitude increase with flow rate, indicating stronger transient behavior under high-flow conditions. Beyond the global performance comparison, the flow field is analyzed using $Q_{crit}$ iso-surfaces, mean circumferential velocity, the swirl-intensity parameter $S_{\mathrm{int}}$, relative velocity fields at the PaT operational leading edge, and volute head-loss evaluation. The results show that part-load operation is characterized by strong outlet vortical structures and high residual swirl intensity, while the BEP region corresponds to reduced outlet rotational content. Under overload conditions, the outlet swirl remains limited, but the volute head loss increases significantly, becoming a dominant contributor to the efficiency drop. The study demonstrates that PaT performance cannot be interpreted from outlet swirl alone, but results from the combined effect of residual rotational structures, tongue-region unsteadiness, impeller incidence conditions, and volute dissipation. Full article

Special orthogonal lateral-intake pumping stations on coastal plains face severe lateral deflection and recirculation in the approach channel and forebay. Their underlying evolutionary mechanisms remain unclear, and conventional rectification methods cause substantial hydraulic losses. Using numerical simulations and hydraulic model experiments, this study investigates these unfavorable flow patterns and proposes an original Combined Arc-Frame Flow Straightening Structure (CAFS). This newly proposed CAFS differs from existing structures, achieving effective flow pattern improvement with reduced hydraulic loss. Results reveal three typical flow regimes—S-shaped mainstream, branching flow, and recirculation—and the flow field is partitioned into four hydrodynamic zones: the Mainstream Incident Zone, Mainstream Impact Zone, Mainstream Reflection Zone, and Low-Velocity Recirculation Zone. Axial velocity uniformity and flow angle are strongly influenced by lateral velocity, while turbulent kinetic energy exhibits intrinsic correlations with vertical vorticity. Lateral velocity, recirculation intensity, and hydraulic losses all increase positively with the Froude number. The CAFS effectively suppresses the low-velocity recirculation zone. Quantitative data show an improvement of 46.40 percentage points in uniformity of axial velocity distribution, a reduction of 0.157 rad (9°) in velocity-weighted average angle, 60.98% less turbulent dissipation, and 38.85% less total hydraulic loss. This study clarifies lateral-intake defect mechanisms and provides a valuable engineering reference. Full article

Wave-in-deck slamming generates highly transient impact loads on coastal and offshore deck structures, while the hydrodynamic processes involving air entrapment and its effect on slamming pressures are not fully understood. In this study, regular-wave impacts on a rigid horizontal deck are experimentally investigated using complementary Particle Image Velocimetry (PIV) and Bubble Image Velocimetry (BIV) measurements to systematically examine the evolution of pressure response, flow dynamics (including velocity, vorticity, and turbulence intensity), and entrapped air-cavity dynamics throughout the impact, oscillation, and suction stages. The results show that during the impact stage, the primary pressure peak is generated by rapid upward momentum transfer beneath the deck, while its magnitude and spatial distribution are strongly influenced by the incident wave height and wave period. During the oscillation stage, repeated compression and expansion of the entrapped air cavity influence the post-impact pressure oscillations through continuous redistribution of the surrounding flow. During the suction stage, gravity-driven water withdrawal and progressive flow separation beneath the deck generate a sustained negative-pressure response. The combined pressure, PIV, and BIV measurements provide an experimental framework for characterizing the relationship between flow evolution, cavity dynamics, and pressure response during aerated wave-in-deck slamming. Full article

To improve the energy conversion performance and long-term structural stability of stay vane mixed-flow chemical pumps used for industrial residual pressure recovery, this paper establishes a coupled numerical framework of computational fluid dynamics (CFD) and finite element structural analysis (FEA). The internal flow evolution, radial hydraulic excitation, transient pressure oscillation and impeller mechanical bearing capacity are systematically investigated under three typical flow states: partial load 0.7 Q_d, design condition 1.0 Q_d and overload 1.2 Q_d. The results show that the flow inside the pump is smooth and there is no obvious backflow or separation under the rated working condition, and the energy conversion efficiency is the best. When operating under partial discharge, boundary layer separation and recirculating secondary vortices easily emerge inside the pump passage, which drastically elevates hydraulic energy dissipation. Meanwhile, operating load exerts a remarkable influence on the impeller’s radial hydraulic load and transient pressure oscillation intensity. The radial force and the pressure pulsation amplitude at the impeller outlet are the largest under the small flow condition, and the force is the most stable under the rated working condition. Blade passing frequency dominates the frequency components of transient pressure fluctuations. The maximum von-Mises stress on the impeller concentrates at the filet where blade roots connect with the hub, and this peak value hits 86.3 MPa under partial-load low-flow operating status. Calculated stress values for all three flow rates satisfy the structural safety criteria. The outcomes of this numerical investigation can offer reliable technical support for hydraulic performance optimization and structural dimension design of this type of mixed-flow chemical pump. Full article

Facing the stringent demands of ultra-high pressure fuel injection systems on atomization quality and mixing efficiency, non-circular nozzle geometries have shown significant potential. Biodiesel, as a renewable alternative fuel, suffers from poor atomization due to its high viscosity, low volatility, and large surface tension, posing greater challenges for injector design. Among non-circular designs, the equilateral triangular orifice offers distinct advantages in promoting atomization of high-viscosity fuels and inducing jet axis-switching. This study demonstrates that such triangular nozzles under ultra-high pressure conditions exhibit intense turbulent vorticity at the outlet and distinctive cavitation development, which significantly affect the primary breakup of biodiesel. During spray development, a pronounced axis-switching behavior is observed, characterized by alternating spray cone angles between the major and minor axes. This phenomenon intensifies with higher injection pressure but is mitigated by increased ambient backpressure. The comparative analysis quantitatively establishes these macro–micro coupling characteristics over ultra-high injection pressures of 160–200 MPa, using fixed orifice lengths of 1.5 mm across exit cross-sectional areas ranging from 24,942 to 29,272 μm². The axis-switching process is accompanied by vigorous air entrainment, which significantly enlarges the spray projected area, accelerates liquid breakup, and shortens penetration distance, collectively enhancing the mixing rate and uniformity of biodiesel with air. This work systematically investigates the atomization characteristics and axis-switching behavior of equilateral triangular orifices with varying side lengths when injecting biodiesel under ultra-high pressure conditions, providing an effective technical pathway for the active control of spray morphology and atomization enhancement of biodiesel. Full article

This study presents an unsteady numerical investigation of multi-port lateral jet interaction phenomena on a hypersonic vehicle configuration. An unsteady RANS approach with Menter’s SST k-ω model is implemented to investigate the transient interference mechanisms among single-, triple-, and quintuple-port arrangements, focusing on jet initiation and termination transients. Upstream jets establish bow shocks and a separation zone that progressively degrade the effective pressure ratio for downstream ports. This aerodynamic shielding manifests as nonlinear escalation in coupling intensity, with the quintuple-port configuration exhibiting complex multi-level shock systems distinct from simple superposition of single-port effects. Flow field development completes within approximately 0.5 ms, yet jet-induced vortical structures exhibit pronounced temporal hysteresis during the decay phase, with the high-pressure zone dissipating progressively from upstream to downstream regions. Under steady-state conditions, the quintuple-port arrangement attains a normal force amplification coefficient of 1.044 alongside a pitching moment amplification coefficient of 4.387, illustrating substantial moment augmentation potential inherent to multi-port interference effects. These findings furnish theoretical foundations for Reaction Control System (RCS) port layout optimization and control strategy development in hypersonic flight vehicles. Full article

Recognizing that efficient and high-fidelity simulation of wind farms in mountainous terrain remains a significant challenge, this study adopted an integrated Large Eddy Simulation (LES) and Dynamic Wake Meandering (DWM) approach to conduct medium-fidelity fluid–structure interaction analysis of a wind farm situated on multiple-hill terrain. Furthermore, a comparative investigation with a flat wind farm was conducted to elucidate the coupled effects of turbine layout and terrain conditions on wake characteristics and structural loads. Results show that the terrain-induced vortical structures in the mountainous wind farm significantly enhance the wake meandering amplitude and expansion rate, leading to higher overall turbulence intensity compared to the flat wind farm. Due to the higher wake recovery rate in the mountainous wind farm, the power gain from lateral offset is more limited. Both wind farms reach their maximum power output at a lateral offset of one turbine rotor diameter (1D) under the present setup, beyond which no further increase is observed. The streamwise decay of the terrain-induced flow acceleration effect is identified as the primary cause of power differences among front-row turbines located on distinct hills within the mountainous wind farm. Furthermore, the terrain-induced vortices create more non-uniform inflow conditions in the mountainous wind farm, causing certain turbines to exhibit peak short-term equivalent fatigue loads with a distribution pattern distinct from the flat wind farm. Due to the generally higher turbulence intensity, all turbines in the mountainous wind farm experience increased fatigue loads compared to the flat wind farm. Full article

The eco-revetment structure serves as a link for material, information, and energy exchange between rivers, bank slopes, and organisms, providing a guarantee for the stability of river ecosystems. This study designed a new type of eco-revetment structure based on its characteristics. The internal structure is designed as a cavity, with openings on the top and side walls and curved surfaces connecting the upper and lower components to ensure smooth water flow and stable bank slopes, providing living space for aquatic organisms. By establishing a three-dimensional numerical model and using large-eddy simulation as the main research method, the distribution law of hydraulic characteristics near the revetment structure is observed, and the mechanism of water flow movement is studied. This study indicates that the internal and external water flow conditions of the new ecological revetment structure are complex and exhibit significant spatial heterogeneity. When there are no plants, the flow directions inside and outside the structure are opposite, with hairpin vortices dominating the interior. The presence of plants significantly enhances turbulence intensity and Reynolds stress, resulting in smaller and more diverse vortex structures, and the formation of Karman vortex streets on the leeward side of plants. The movement characteristics of the revetment structure vary in different regions: in region C, when there are no plants, the value of (|Q2| + |Q4|)/(|Q1| + |Q3|) is greater than 1.5, and it increases to 3 when plants are present. The ratio for region B is 0.83 and 0.8, while for region A it is 1.02 and 1.17. When there are no plants, the Reynolds stress contribution in region A is uniform, region B shows a “hyperbolic” distribution, and the proportion of S2 and S4 at the top of region C increases sharply. Plants increase the contribution of the top of the region C to three to five times that of no plants. The complex water flow environment significantly changes the mechanism of water flow movement. The Reynolds stress contribution and turbulent kinetic energy fit well. The presence of plants leads to a Reynolds stress contribution and turbulent kinetic energy value that are about three times higher than without plants. When there are no plants, the turbulent structure within the structure is mainly influenced by S1 and S3, while when there are plants, S2 and S4 dominate the turbulence. This article provides a solid theoretical foundation and quantitative experimental basis for the study of nearshore water flow mechanisms in ecological revetment structures. Full article

To mitigate the negative impacts of traditional rigid revetments on river ecosystems, this study focuses on perforated plate grid revetments, aiming to reveal the hydrodynamic mechanisms and parameter collaborative optimization pathways that simultaneously achieve anti-scour stability and ecological water exchange. A series of flume scour tests were conducted, combined with high-resolution large eddy simulation (LES) validated by experimental data, to systematically analyze the regulatory effects of key design parameters—such as opening ratio and longitudinal offset angle—on near-bottom flow velocity attenuation, vortex structures, and water exchange efficiency. The results indicate that a prototype parameter combination of 0.25 m grid height and 0.50 m plate grid spacing can reduce local scour depth by about 30% and enhance vertical exchange through the synergy of jetting from the openings and internal vortices. The longitudinal offset of adjacent holes may enhance the transverse water exchange but may also significantly reduce the longitudinal exchange intensity; hence, further research is needed. A hole-to-baffle height ratio greater than 0.40 is identified as a critical threshold for improving exchange efficiency. This study proposes a collaborative design framework in which grid spacing controls scour safety and aperture parameters regulate exchange functions, providing an experimental basis for the precise design and performance enhancement of ecological revetments. Full article

The brake–release stability of electro-hydraulic thrusters (EHTs) significantly affects the safety of hydraulic braking systems, especially under low-temperature conditions with varying fluid viscosity. Most existing studies have focused on macroscopic braking characteristics, while the internal flow field variation and vortex evolution mechanism during the brake–release process remain insufficiently explored. In this work, transient CFD simulations are conducted to investigate vortex formation rules and flow field characteristics inside an EHT. Three typical vortex structures denoted as α, β, and γ are identified, and the independent and coupling influences of fluid dynamic viscosity and motor speed on vortex intensity and piston-bottom pressure are quantitatively analyzed. The results show that vortices α and β trigger flow disorder and additional hydraulic energy loss, while vortex γ optimizes flow uniformity and assists piston extension. Higher fluid viscosity exacerbates vortex development and pressure fluctuation, while increasing motor speed accelerates transient flow field evolution. This study clarifies the internal flow mechanism of EHT brake–release behavior and provides reliable parametric guidance for optimizing the low-temperature performance of electro-hydraulic braking systems. Full article

Breakwater construction at meso-tidal ports fundamentally alters near-field hydrodynamics and drives harbor sedimentation, yet the three-dimensional mechanisms linking entrance geometry to sediment flux remain poorly quantified. Here, we apply a validated Delft3D tidal–sediment coupled model to Caofeidian Port, Bohai Bay, comparing pre-construction baseline conditions against four entrance width scenarios (400, 300, 250, and 200 m). Breakwater enclosure reduces depth-averaged harbor velocities by 61.9–63.2% during spring tides, while generating tip-jet velocities of 1.41–1.53 m s⁻¹ at the eastern breakwater head—exceeding pre-construction maxima by 14–18%. The eastern tip produces an ebb vortex (radius ~230 m; peak vorticity 0.034 s⁻¹) approximately 34% larger and 62% more intense than its flood counterpart, driving vortex-assisted sediment recirculation toward the harbor interior despite ebb-dominant background velocities. Reynolds flux decomposition confirms that the eastern tip-vortex sector contributes ~39% of net sediment import (advective component: −0.7%), directly quantifying vortex-assisted recirculation as an independent transport mechanism. Bed shear stress falls below the critical erosion threshold (${\tau }_{ce}$ = 0.22 Pa) across 76.8% of the harbor area during spring tides (robust lower bound ~60% under wave-coupling correction), creating a structurally stable depositional interior, while the near-entrance zone sustains persistent tidal-cycle resuspension. Asymmetric tidal pumping—flood-phase open-sea SSC of 0.088 kg m⁻³ versus ebb-phase harbor SSC of 0.032–0.041 kg m⁻³—drives net spring-tide sediment import of 14.8 × 10⁶ kg per cycle (wave-coupled upper bound: 17.8–19.2 × 10⁶ kg per cycle). Entrance width reduction from 400 to 300 m achieves a favorable sedimentation-to-water exchange trade-off (marginal efficiency ratio 1.23), whereas further reduction to 200 m indicates onset of hydraulic choking. The marginal efficiency ratio declines sharply from 1.23 (400 → 300 m) to 1.03 (300 → 250 m) to 1.01 (250 → 200 m), indicating a hydraulic transition within the 250–300 m range that warrants targeted refinement in future studies. Full article

Erosive wear in pipe elbows subjected to liquid–solid two-phase flow is a major cause of material degradation and service failure in industrial piping systems. In this study, erosion characteristics of pipe elbows were investigated through erosion mapping experiments and numerical simulations. The effects of flow velocity and particle diameter on erosion location and intensity were analyzed. Erosion was found to be mainly concentrated on the outer wall of the elbow within the angular range of 10° to 90°, and both erosion intensity and affected area increased with increasing particle diameter and flow velocity. Dean vortices were shown to play an important role in particle transport and erosion distribution, especially for small particles. Inspired by the ribbed morphology of shells, a biomimetic elbow was further designed and evaluated through an orthogonal numerical study considering flow velocity, particle diameter, rib number, and rib diameter. The results indicate that the ribbed structure can effectively improve erosion resistance by altering particle trajectories, reducing particle impact probability, and dissipating kinetic energy through low-velocity rotating flow between adjacent ribs. This finding provides useful inspiration for addressing erosive wear problems in engineering applications. Full article

The structural integrity of hydraulic structures is frequently weakened by local scour processes downstream of weirs. This study investigates the relationship between hydraulic parameters and erosion patterns to improve the predictability of bed deformation. The research methodology integrates detailed field measurements from the Radomka River in Piaseczno with laboratory experiments using a 1:30 physical scale model of the existing weir. Bed shear stress demonstrated the strongest correlation with maximum scour depth (r ≈ 0.93; RMSE ≈ 0.0032), as it directly represents the tangential force acting on sediment particles at the bed surface, which controls their entrainment, transport capacity, and ultimately the intensity of local scour development, whereas near-bed velocity showed weak and non-significant dependence (r ≈ 0.26; ${\rho }_s$ ≈ −0.11). This weak dependence reflects the dominance of turbulence-induced velocity fluctuations and localized vortical structures in the near-bed region, which obscure the relationship between mean velocity and sediment mobilization. The relationships between mean velocity, Froude number, and scour depth were moderate (r ≈ 0.63–0.73) and showed nonlinear characteristics, confirmed by HSIC values up to 9.1 × 10⁻³, due to the complex interaction between flow structures and evolving bed morphology. This nonlinearity results from the interaction between turbulent flow structures, jet-induced vortices, and the dynamically evolving bed morphology, combined with the threshold-controlled and nonlinear response of sediment transport to hydraulic forcing. Among all tested parameters, bed shear stress ranked as the dominant predictor of scour depth, outperforming velocity-based indicators. These findings imply that including bed shear stress parameters significantly improves hydraulic structure safety assessments. This study based on 11 experimental runs concludes that a combined field and laboratory approach provides a robust framework for river engineering. Finally, an improved understanding of erosion mechanisms, as presented in this work, enhances the prediction of local scour development and supports the design of more resilient hydraulic infrastructure. Full article