Search Results (1,461)

A three-dimensional numerical investigation is conducted to clarify the internal pressure and velocity distributions in a hydraulic turbine under multiple operating conditions. The study aims to identify the main high-gradient regions and the influence of operating parameters on the internal flow field. The incompressible single-phase Navier–Stokes equations are solved using the SST k-ω turbulence model. Eleven operating conditions with different guide vane openings, net heads, output powers, and discharges are simulated using a full-passage turbine model with mass flow inlet and static pressure outlet boundary conditions. The numerical results are validated against experimental performance data. The results show that the pressure and velocity fields exhibit generally symmetric distributions in the circumferential and axial directions, whereas strong local gradients appear in the rotor–stator interaction region. Local high-pressure and high-velocity zones are mainly observed near the blade leading edges, while low-pressure and low-velocity regions develop near the trailing edges, runner cone, and draft tube. Increasing the net head raises the overall pressure and velocity levels and enhances the low-pressure and low-velocity regions in the draft tube. Under a fixed head, increasing the guide vane opening mainly affects the flow distribution around the stay and guide vanes and modifies the flow structure in the runner cone and draft tube. These findings provide a systematic numerical characterization of the pressure and velocity distributions in the turbine and help identify critical regions for further hydraulic performance analysis and flow field optimization. Full article

Hydrogen enrichment of compression ignition (CI) engines has emerged as a promising strategy to simultaneously enhance thermal efficiency and reduce carbon-based emissions. This study numerically investigates how hydrogen enrichment affects engine performance and emissions in methanol–diesel dual-fuel CI engines, a combustion mode gaining increasing attention for replacing fossil diesel with sustainable fuels, particularly in hard-to-abate sectors such as maritime transport. The simulations are based on the Unsteady Reynolds-Averaged Navier–Stokes (URANS) equations, incorporating the RNG k–ε turbulence model, the Eddy Dissipation Concept (EDC) for turbulence–chemistry interaction, and the G-equation for turbulent premixed flame propagation. The numerical model is validated against experimental data for in-cylinder pressure and heat release rate at 45% methanol substitution ratio (by energy). The results indicate that increasing the hydrogen enrichment ratio (HER, defined on an energy basis) from 5% to 20% raises the Sauter mean diameter (SMD) of the diesel fuel from 20.2 µm to 28.0 µm (+38%), driven by reduced aerodynamic breakup intensity associated with modified gas-phase properties under hydrogen enrichment. Furthermore, hydrogen’s elevated adiabatic flame temperature and superior mass diffusivity intensify combustion, raising peak in-cylinder pressure from 75.2 to 79.1 bar (+5.2%), amplifying the peak heat release rate from 129 to 211 J/°CA (+63.6%), and elevating maximum in-cylinder temperature from 1542 to 1735 K (+193 K). Under the investigated CFD operating conditions, these thermodynamic gains translate into an engine-level 6% improvement in indicated thermal efficiency and a 14% reduction in indicated specific fuel consumption (accounting for hydrogen, methanol, and diesel) at HER 20%. On the emissions front, CO₂ declines by 24% in direct proportion to the carbon-containing fuel mass displaced by hydrogen substitution, while NOₓ increases approximately twofold from 0.10 g/kWh at HER 0 to 0.21 g/kWh at HER 20, driven by peak temperature elevation. These findings establish hydrogen-enriched methanol–diesel dual-fuel combustion as a viable pathway toward high-efficiency, low-carbon CI engine operation for heavy-duty transport applications. Full article

This work presents a mathematical and numerical framework for the design and analysis of a remotely operated vehicle (ROV) intended for shallow-water reef exploration. The vehicle consists of an open-frame structure with a sealed pressure housing and a four-thruster propulsion system that enables omnidirectional maneuverability and stable low-speed operation. The hydrodynamic behavior of the ROV is modeled using the incompressible Reynolds-averaged Navier–Stokes equations, which are solved numerically to obtain the velocity and pressure fields around the vehicle. Thruster-induced flow is represented through a Multiple Reference Frame (MRF) formulation, allowing thrust generation and momentum exchange to be resolved directly from the governing equations without prescribing artificial source terms. The propulsion model is supported by experimental bollard-pull characterization of T200 thrusters, from which quadratic thrust laws were identified. A quantitative validation against published experimental data shows deviations within 6–9% and a root-mean-square error (RMSE) of approximately 1.6 N, confirming the accuracy of the proposed thrust model. The CFD-predicted axial force ($F_Z\approx -17.60\mathrm{N}$) was further shown to be consistent with the experimentally derived thrust law when evaluated at the corresponding equivalent operating condition. Structural response is evaluated through a one-way fluid–structure interaction (FSI) strategy, in which the hydrodynamic loads obtained from the CFD solution are transferred to a linear elastic structural model. The validity of the one-way coupling assumption is supported by explicit displacement-to-length ratios in the range $\delta /L\sim$ 10⁻⁵–10⁻³, confirming negligible geometric feedback on the flow field. The results show that the combined CFD–FSI formulation provides physically consistent predictions while remaining computationally efficient. The aluminum configuration exhibited a maximum von Mises stress of approximately 21.1 MPa, remaining safely within the elastic regime, whereas the ABS configuration reached a maximum displacement of 2.9 mm, indicating substantially higher structural compliance. Overall, the experimentally validated propulsion model, quantitatively supported CFD predictions, and asymptotically justified one-way FSI coupling constitute the main contributions of this study, providing a reproducible and physically consistent methodology for the analysis and optimization of reef-class ROVs. Full article

Steelmaking is one of the most important industries worldwide due to many products being made with different kinds of steel or cast iron; during processing, pig iron and scrap are founded in furnaces and then transported in ladles to be cast in tundishes towards strains to produce steel billets, which are treated in a secondary manufacturing process to produce products like wires and profiles. Then, it is necessary to pay attention to every process and establish rules for safe operational practices, avoid interruptions in production, reduce risks and maintain quality. Thus, the purpose of this research is to study the hydrodynamic behavior of five stopper rods with different but basic geometrical configurations. Stopper rods are devices that are used to control the fluid flow in tundishes to allow or avoid a steel fluid drain. Stopper rods are placed to allow or avoid the liquid steel passing out towards the molds in the deepest holes in the tundishes. Management, drive and mass transport are important parameters to analyze for casting molten steel. After analyzing the hydrodynamic performance of these five stopper rods, and according to the results obtained, two more new designs were created and tested in real industrial trials, and the results are described in detail. Additionally, a study about the counting of the inclusions trapped in the rod walls is also shown to evaluate every design, with the main goal being to retain the flows passing across the stopper rod and the exit nozzle and to avoid clogging problems in order to keep constant the casting of molten steel. Hydro-dynamic analysis was carried out by solving the Navier–Stokes equation using the k-ε turbulence model using Computational Fluid Dynamics (CFD). Full article

This study investigates the hydrodynamic performance of the KVLCC2 tanker in deep and shallow water using computational fluid dynamics (CFD) simulations, focusing on resistance and self-propulsion with both ducted and non-ducted propellers. The Reynolds-averaged Navier–Stokes (RANS) equations, coupled with the SST k-ω turbulence model, are solved using STAR-CCM+ to analyze ship resistance, open-water propeller characteristics, and self-propulsion factors. Validation against experimental data confirms the numerical accuracy, with uncertainties below acceptable thresholds. In deep water, the body force propeller and body force ducted propeller methods are validated against the discretized propeller approach, yielding errors under 5%. The ducted propeller enhances open-water efficiency but results in higher thrust deduction and lower wake fractions, leading to reduced hull and overall propulsive efficiencies compared to the non-ducted case. In shallow water, as the depth-to-draft ratio (H/T) decreases to 1.5, added resistance, sinkage, and trim increase sharply due to blockage effects. The ducted configuration mitigates these penalties, achieving a 20.8% power reduction at H/T = 1.5. Added self-propulsion factors reveal that the duct improves hull efficiency and offsets shallow-water losses, enhancing propulsive efficiency. Flow field analysis shows accelerated stern wakes and asymmetric structures in shallow water, with the body force methods providing consistent predictions despite minor discrepancies in extreme conditions. This research highlights the efficacy of ducted propellers in shallow water and the reliability of body force methods for efficient simulations, offering insights for ship design in restricted depths. Full article

This study analyzes the effects of different moonpool configurations on drillship hydrodynamics using the Reynolds-averaged Navier–Stokes (RANS) equations. A three-dimensional numerical wave tank is established to realize the prediction and validation of the hydrodynamic performance of irregular waves and the interaction between irregular waves and structures. Combined with the selection of the drillships with relatively favorable resistance performance among different moonpool configurations under calm-water navigation conditions, further studies are carried out on the motion characteristics and drag-reduction optimization of the rectangular- and square-moonpool drillships under irregular wave conditions. Comparative analysis of the numerical results shows that different moonpool shapes result in different drag-increase effects under calm-water conditions, and the moonpool-induced drag increase mainly originates from added residuary resistance. Relative to the non-moonpool baseline drillship, the installation of a moonpool under irregular wave conditions notably elevates the resistance amplitude and amplifies the heave and pitch responses, with a more prominent impact observed on pitch, while also modifying the natural frequency characteristics of the moonpool-equipped drillship. Introducing appropriate rounded corners at the bottom of the moonpool can effectively reduce the resistance of the moonpool drillship and significantly decrease the amplitudes of heave and pitch responses under irregular wave conditions. Based on the present study, a bottom rounded-corner radius of 40 mm effectively improves the hydrodynamic performance of the moonpool drillship in irregular waves. The numerical results provide direct theoretical and design guidance for drag reduction and motion-performance enhancement of moonpool-equipped drillships, highlighting their engineering applicability. Full article

This paper presents a meshless collocation technique for the fourth-order transient stream function formulation of the Navier–Stokes equations. The technique employs a hybrid kernel function and is augmented by the ghost point method and Picard iteration. The reduction in unknowns inherent in this stream function approach simplifies the solution process. Introducing vorticity and stream functions enables mathematical reformulation of the coupled, time-dependent Navier–Stokes system as a fourth-order partial differential equation in one variable. The Gaussian–cubic backward substitution method and time difference method are used to solve the corresponding equation, in which the nonlinear part is generally transformed into linear equations through Picard iteration methods. This paper simulates three flows to prove the feasibility of the scheme. Full article

In this work we present the development and application of a mesh adaptation tool on hybrid unstructured meshes for immersed boundary volume penalization methods in the computational fluid dynamics software from ONERA, DLR, and Airbus. This mesh adaptation tool is capable of refining elements around geometries immersed in unstructured meshes made of different types of elements, like tetrahedra, hexahedra, prisms, and pyramids. This feature allows us to simulate fluid flow problems with the immersed boundary method not only on Cartesian meshes but on general hybrid unstructured meshes. Of special interest in this work is the simulation of turbulent fluid flows in aerodynamics through the numerical solution of the Reynolds-averaged Navier–Stokes equations either on unstructured meshes with only immersed geometries or on unstructured body-fitted meshes along with immersed geometries. As part of the benchmarking, we simulate the subsonic flow past the high-lift multi-element airfoil. The reported numerical simulations are in good agreement with their corresponding full body-fitted meshes. Full article

This article proposes a novel approach for dealing with the time-fractional Navier–Stokes equations via the natural generalized Laplace transform decomposition method (NGLTDM). This hybrid method utilizes both the natural generalized Laplace transform (NGLT) and a decomposition method. The method is correct because the series solutions become more accurate when more terms are added. We establish precise theorems that verify the existence of solutions and the convergence of the series. The analysis shows that the suggested method is more general than the Homotopy Perturbation Method (HPM) and the Adomian Decomposition Method (ADM). Also, this approach can be applied to handle difficult fluid dynamics problems governed by the Navier–Stokes equations. This study enhances analytical methodologies for fractional-order flow models. Full article

The quasi-steady low-Reynolds-number flow induced by a linear chain of multiple slip spheres translating along their common axis in a Newtonian fluid is investigated. The particles are allowed to differ in radius, Navier slip coefficient, migration velocity, and interparticle spacing. A semi-analytical solution of the governing Stokes equation is obtained using a boundary collocation method. Hydrodynamic interactions among the particles are shown to be significant under appropriate geometric and surface conditions. For the two-sphere configuration, the computed hydrodynamic forces agree closely with previously published asymptotic solutions derived via the twin multipole expansion method. In the three-sphere case, the presence of a third particle substantially modifies the forces acting on the other two, demonstrating non-negligible many-body interaction effects. The interaction strength is found to be more pronounced for smaller particles or those with lower slip coefficients. Calculations for longer particle chains further reveal a clear hydrodynamic shielding effect within the assembly. Full article

We develop a structural framework for the three-dimensional incompressible Navier–Stokes equations in which the nonlinear dynamics are reorganized in terms of triadic interactions, dyadic shells, and helical modes. Within this formulation, all interactions are classified into Low–Low, Low–High, and High–High channels, and it is shown that the Low–Low and Low–High contributions are perturbatively controlled through scale-localized estimates without introducing external assumptions. Consequently, potentially non-perturbative contributions are confined, within the present framework, to a class of same-scale High–High interactions. This class is further reduced, through geometric and dynamical constraints, to a coherent core characterized by amplitude activity and low phase drift. The resulting reduced dynamics is expressed in terms of family-level phase variables and associated curvature quantities. The main result establishes a quantitative residence-time compression principle for this coherent regime. Specifically, it is shown that intervals on which both amplitude activity and low phase drift persist must have small total measures, due to an absolute-value coercivity property of the curvature combined with bounded-variation control of the phase dynamics. This implies that coherent same-scale interactions cannot occupy a macroscopic portion of any bounded time interval, even though local re-entry into low-drift configurations is not excluded. Consequently, the nonlinear transfer associated with coherent triads becomes temporally localized and admits a shellwise compressed representation. These results provide a structurally reduced description of a candidate mechanism for cumulative same-scale amplification within the present dyadic–triadic framework. They do not claim a framework-level structural exclusion of the global regularity problem. Rather, they identify and analyze, within an explicit structural setting, a minimal mechanism for non-perturbative amplification, and establish a quantitative constraint on its temporal persistence. Full article

Two-phase displacement between cement slurry and drilling fluid in wellbore systems is inherently nonlinear, interface-dominated, and strongly affected by geometric confinement, posing substantial challenges to efficient and stable numerical simulation. Conventional CFD approaches rely on mesh discretization and explicit interface tracking, which become computationally demanding and sensitive to grid quality in complex geometries and convection-dominated regimes. To address these limitations, this study develops a unified physics-informed neural network (PINN) framework for directly solving the coupled incompressible Navier–Stokes and Volume of Fluid (VOF) equations governing pressure-driven displacement. The framework is first validated against canonical transient flows and then applied to two-phase displacement in parallel-plate channels, semicircular bends, and a casing–annulus geometry representative of well cementing operations. The predicted velocity, pressure, and volume fraction fields exhibit strong agreement with ANSYS Fluent (2024R1) results, with relative errors generally around 5%, thereby demonstrating physical consistency and numerical stability without mesh generation or pressure–velocity splitting, while also showing favorable computational efficiency for the cases considered. Sensitivity analyses demonstrate that a smoother casing-shoe geometry significantly enhances PINN convergence, while higher Péclet numbers deteriorate training stability by increasing convection-dominated stiffness and optimization difficulty. The results demonstrate that the proposed PINN framework, with its mesh-free and geometrically flexible characteristics, is a promising approach for modeling multiphase displacement in cementing applications. Full article

In air jet looms, relay nozzles are critical components in governing airflow velocity and air consumption during the weft insertion process. Although computational fluid dynamics (CFD) offers high-fidelity simulation for aerodynamic analysis, its computational burden hinders its practicality in iterative aerodynamic design of relay nozzles. To address the challenge, this study proposes a data-driven framework integrating a Chebyshev polynomial Kolmogorov–Arnold Network (Chebyshev KAN) surrogate model with an Improved Multi-objective Red-billed Blue Magpie Optimizer (IMORBMO). The accuracy of the Chebyshev KAN model was benchmarked against conventional multilayer perceptrons (MLP), convolutional neural networks (CNN), and the standard Kolmogorov–Arnold Network (KAN). Experimental results demonstrate that the Chebyshev KAN model achieves the lowest mean absolute error (MAE) of 0.103 for airflow velocity and 0.115 for air consumption. Building upon the non-dominated sorting and crowding distance strategies, IMORBMO was developed, incorporating an adaptive mutation mechanism by information entropy for improvement of convergence, diversity, and uniformity of the Pareto-optimal solutions. Comprehensive evaluations on the ZDT and WFG benchmark suites confirm that the IMORBMO consistently attains the best and highly competitive performance, yielding the lowest generation distance (GD), inverted generational distance (IGD) values and the highest hypervolume (HV). Applied to the aerodynamic optimization of a relay nozzle, the proposed framework delivers an optimal aerodynamic design that increases airflow velocity by 10.5% while reducing air consumption by 15.4%, as verified by CFD simulation. The steady-state flow field was simulated by solving the Reynolds-Average NavierStokes equations with the k–ω turbulent model, utilizing Fluent 2025.R2. No-slip wall, inlet pressure and outlet pressures are boundary conditions to the relay nozzle surfaces. This work establishes a computationally efficient and accurate optimization paradigm that holds significant promise for aerodynamic design and other complex real-world engineering applications. Full article

This paper investigates co-continuous structures in immiscible polymer blends through three-dimensional (3D) computational calculations based on a multiphase phase-field equation for fluid flow. The mathematical model describes phase separation with the Cahn–Hilliard (CH) equation and fluid motion with the incompressible Navier–Stokes (NS) equations. Both polymers are treated as Newtonian viscous fluids, and the model includes surface tension, viscosity, and volume fraction effects. A semi-implicit finite difference method (FDM) solves the CH equation, and a projection method maintains the incompressibility of the flow field. Multigrid techniques solve the nonlinear systems efficiently. In addition, a connectivity-based detection algorithm determines whether a phase forms a connected structure that reaches all boundaries of the numerical domain. The numerical results show that the morphology changes from a droplet–matrix structure to a co-continuous structure as the volume fraction increases. The interfacial area per unit volume reaches a local maximum near the transition between these two regimes. Full article

Precise manipulation of two-phase flow in micro-confined electrowetting pixels is limited by contact angle hysteresis (CAH). To elucidate this non-equilibrium process, we establish a high-fidelity electrohydrodynamic (EHD) phase-field simulation framework. The model rigorously couples Navier–Stokes equations with molecular kinetic theory (MKT) to characterize energy dissipation at the three-phase contact line (TCL) and further integrates charge transport kinetics. Numerical results reveal CAH is driven by physical pinning and interfacial charge trapping, with the latter dominating interfacial retreat and causing significant residual displacement. Furthermore, analysis shows alternating current (AC) waveforms mitigate charge accumulation and promote depinning via micro-oscillations, minimizing the hysteresis loop compared to direct current (DC) waveforms. Additionally, an overdrive strategy utilizing a suprathreshold Maxwell stress pulse rapidly overcomes static friction. This strategy significantly improves transient dynamics, substantially reducing the time to reach 90% of the steady-state target from 19.6 ms (under standard DC waveform driving) to 7.4 ms. This work provides a comprehensive theoretical basis and design criteria for optimizing active driving strategies in optofluidic and digital microfluidic systems. Full article