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The droplet evaporation in sprays and clouds is largely influenced by the interacting surrounding droplets. This study presents a numerical investigation on the evaporation dynamics of two inline interacting droplets in a high-temperature vapor domain using ANSYS Fluent. Several methods are available to solve the multiphase flow problems with phase change, including level set, phase field, volume of fluid (VOF), and hybrid techniques. In the present study, the multiphase model equations are solved in the framework of the VOF method, which is a well-established and robust solver for multiphase flows with excellent volume conservation properties. The Lee model is used to handle the evaporative phase change at the interface. The droplet spacing, sizes, and arrangement pattern of differently sized droplets are the key parameters varied to explore their effects on the evaporation rate, droplet velocities, and inter-droplet distance. For equal-sized droplets, the evaporation of the trailing droplet slows down due to the low-temperature buffer layer of the droplet vapors generated by the evaporation of the leading droplet; the effects decrease as the initial spacing is increased. For two droplets at center-to-center distances of 2do and 6do, the evaporation of the trailing droplets reduces by 20.8% and 7%, respectively. Decreasing the size of the trailing droplet increases its evaporation rate since the smaller droplet experiences more temperature gradients as it escapes out of the influence of the leading drop buffer layer. For a smaller to larger droplet diameter ratio of 0.9, the evaporation rate of the trailing droplet is reduced by ~26% than expected. However, for the diameter ratio of 0.5, this reduction is only 12.5%. Regarding the arrangement pattern of different-sized droplets, the overall evaporation rate is lower when the bigger droplet follows the smaller one. The fact is attributed to close interaction followed by the coalescence of the bigger droplet with the leading smaller droplet, resulting in a single bigger droplet. [ABSTRACT FROM AUTHOR]

Tannin foam is a new functional material. It can be widely applied to the automobile industry, construction industry, and packaging industry due to its wide range of raw materials, renewable, easily degraded, low cost and almost no pollution. Preparing tannin foam is a very complex process that includes high temperature, two phases, mechanical agitation, and phase change. To investigate the influence of the stirring velocity and paddle shape, simulation was calculated by making use of the volume of fluid (VOF) method and multiple reference frame (MRF) method in a three-dimensional flow field of tannin-based foaming precursor resin. The gas holdup and velocity magnitude were analysed with various conditions of mechanical velocities and paddle shape in the stirring flow field. The result shows the higher the velocity, the greater the disturbance and paddle shape between the eggbeater and the Rushton turbine, obviously the paddle shape of the eggbeater with a wider range of agitation, which can entrap more air into the tannin-based foaming precursor resin in a short time. Especially when the speed is 1500 rpm, the flow field of the Rushton turbine comes out of a ditch, which decreases the efficiency of mass transfer; there is less air to mix into the tannin-based foaming precursor resin, which causes unevenness. At the same time, the eggbeater shows the marvelous capability of hybrid as it has two vortexes and multiple cycles that make a difference from the Rushton turbine, which has only one vortex and two upper and lower loops; the structure makes the flow field more stable allowed evenness of flow field tannin-based foaming precursor resin. The results reveal that it is beneficial for tannin-based foaming precursor resin to use an eggbeater with a speed of 1500 rpm to reduce the consumption of resources while obtaining a uniform flow field. [ABSTRACT FROM AUTHOR]

This study evaluates computational fluid dynamics (CFD) turbulence closures for Reynolds-averaged Navier-Stokes (RANS) equations against experimental data to model complex open channel flows, like those occurring over dune-shaped salmon spawning nests called "redds". Open channel flow complexity, characterized by near-bed turbulence, adverse pressure, and free surfaces, requires suitable turbulence closure capable of capturing the flow structure between streambed and water surface. We evaluated three RANS models: Standard k - ω, shear-stress transport (SST) k - ω and realizable k - ε, along with four wall treatments for the realizable k - ε: Standard, and scalable wall functions, enhanced wall treatment, and an unconventional closure combining standard wall function with near-wall mesh resolving the viscous sublayer. Despite all models generally capturing the bulk flow characteristics, considerable discrepancies were evident in their ability to predict specific flow features, such as flow detachments. The realizable k - ε model, with standard wall function and mesh resolving viscous sublayer, outperformed other closures in predicting near-wall flow separations, velocity fields, and free surface elevation. This realizable k - ε model with a log-layer resolved mesh predicted the free surface elevation equally well but lacked precision for near-wall flows. The SST k - ω model outperformed in predicting turbulent kinetic energy and provided better predictions of the near-boundary velocity distributions than realizable k - ε closure with any of the conventional wall treatments but overestimated the separation vortex magnitude. The standard k - ω model also overestimated near-wall separation. This study highlights the variability in accuracy among turbulence models, underlining the need for careful model selection based on specific prediction regions. [ABSTRACT FROM AUTHOR]

Open-channel flows over a drop structure with a trench, often seen in urban rivers, may cause an oscillating phenomenon of hydraulic jumps depending on the trench geometry and hydraulic conditions. The oscillating hydraulic jumps are accompanied by large-scale water-surface variations with wave breaking, and numerical predictions of such flows are challenging in hydraulics. Using unsteady Reynolds-averaged Navier-Stokes simulations of air-water two-phase flows, we attempted to predict an oscillating hydraulic jump at a drop structure with a trench observed in our laboratory experiment. Several high-Reynolds-number turbulence models were applied, and the effects of turbulence models and grid resolutions on predicting the oscillating hydraulic jump were investigated. Turbulence models other than the k–ω SST model resulted in a steady-state flow with no oscillations regardless of the grid resolution. The k–ω SST model succeeded in predicting the oscillating hydraulic jump using a fine grid while the flow became a quasi-steady state using a coarse grid. Moreover, the period of the oscillation and the flow fields are in good agreement with the experimental results. The k–ω SST model has the ability to predict oscillating hydraulic jumps, including wave breaking, because this model accurately simulates flows with separations or stagnations under adverse pressure gradients. [ABSTRACT FROM AUTHOR]

Fuel spray modeling plays a critical role during modern gasoline direct injection (GDI) engine development due to fuel injection's dominant impact on engine performance and emissions as well as the complex physical processes involved. In engineering three-dimensional (3D) computational fluid dynamics (CFD) simulations, the liquid-phase fuel atomization, evaporation, and mixing are usually modeled with the discrete droplet model (DDM) adopting a Lagrangian approach for multiphase CFD simulations. To this end, general practices heavily depend on the reduced order characterization of the injector nozzle flow. However, such simplified injector modeling may lead to insufficient representations of the complex spray dynamics. To tackle this problem, this study proposes a novel workflow to numerically evaluate GDI sub-cooled and flash-boiling sprays under engine-relevant conditions using a side-mounted GDI injector together with real gasoline fuel properties. The workflow introduces a one-way coupling (OWC) method leveraging high-fidelity nozzle flow simulations to provide realistic boundary conditions to the Lagrangian injector model. The proposed workflow was first verified in a constant volume chamber (CVC) environment and then implemented in a practical GDI engine setup to study spray morphology, fuel-air mixing, and wall-wetting propensity. In addition, detailed comparison was performed between the OWC method and the conventional rate of injection (ROI) routine. Quantitative analysis of spray characteristics was conducted to highlight possible source of discrepancies of the conventional ROI method. [ABSTRACT FROM AUTHOR]

The Japan Atomic Energy Agency (JAEA) is developing an evaluation method for a two-phase flow in the reactor core using simulation codes based on the volume of fluid (VOF) method. However, it is impossible to simulate boiling on the heating surface in large-scale domains, such as fuel assemblies, using this simulation method because simulating boiling based on the VOF method requires fine meshes to resolve the initiation of boiling. Therefore, the JAEA started developing a simplified boiling model (SBM) for the two-phase flow simulation in fuel assemblies. In the SBM, the motion and growth equations of a bubble are solved to obtain their diameter and time length at the detachment, the size scale of which is within/around the calculation grid size of the numerical simulation. This information is given as the vapor injection flow rate for the boundary condition on the heating surface. JUPITER calculates the bubble behavior with a scale of more than several millimeters. Using the developed SBM, this study simulates convection boiling on a vertical heating surface. A comparison between the simulation and experimental results showed good reproducibility of the heat flux and velocity dependency on the passage period of the bubble.

Wave impact is a strongly nonlinear interaction between waves and structures, and its load usually has the characteristics of a large peak value and short duration. In recent years, the extreme environment has frequently led to severe wave impacts on marine structures, resulting in loss of life and property, thus making the issue of wave impact become a great concern. For the complicated impact process, the theoretical analysis and model experiments can only provide simplified analytical solution and limited information on the slamming flow field. Therefore, numerical simulation has gradually become an effective means to study the issue of wave impact. Scholars at home and abroad have conducted a large number of numerical investigations on the load characteristics of wave impact, impact process, and its influencing factors on marine structures, gaining numerous important research conclusions. In this paper, the current progress, existing methods, and important conclusions of the numerical study of wave impact on marine structures are reviewed, which can provide useful references for further research on the numerical simulation of wave impact.

The droplet evaporation in sprays and clouds is largely influenced by the interacting surrounding droplets. This study presents a numerical investigation on the evaporation dynamics of two inline interacting droplets in a high-temperature vapor domain using ANSYS Fluent. Several methods are available to solve the multiphase flow problems with phase change, including level set, phase field, volume of fluid (VOF), and hybrid techniques. In the present study, the multiphase model equations are solved in the framework of the VOF method, which is a well-established and robust solver for multiphase flows with excellent volume conservation properties. The Lee model is used to handle the evaporative phase change at the interface. The droplet spacing, sizes, and arrangement pattern of differently sized droplets are the key parameters varied to explore their effects on the evaporation rate, droplet velocities, and inter-droplet distance. For equal-sized droplets, the evaporation of the trailing droplet slows down due to the low-temperature buffer layer of the droplet vapors generated by the evaporation of the leading droplet; the effects decrease as the initial spacing is increased. For two droplets at center-to-center distances of 2do and 6do, the evaporation of the trailing droplets reduces by 20.8% and 7%, respectively. Decreasing the size of the trailing droplet increases its evaporation rate since the smaller droplet experiences more temperature gradients as it escapes out of the influence of the leading drop buffer layer. For a smaller to larger droplet diameter ratio of 0.9, the evaporation rate of the trailing droplet is reduced by ~26% than expected. However, for the diameter ratio of 0.5, this reduction is only 12.5%. Regarding the arrangement pattern of different-sized droplets, the overall evaporation rate is lower when the bigger droplet follows the smaller one. The fact is attributed to close interaction followed by the coalescence of the bigger droplet with the leading smaller droplet, resulting in a single bigger droplet.

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In this study, the implicit Finite Volume Method (FVM) based on Reynolds-Averaged Navier-Stokes (RANS) equations are used to simulate the flow past a hydrofoil that is submerged in the vicinity of the free surface of water. To simulate the turbulent flow around the hydrofoil surface, realizable k-e turbulence model is used. The Volume of Fluid (VOF) method is incorporated into the numerical simulation to capture the interface between water and air. The free surface wave generated by the stream around NACA 0012 hydrofoil is computed and compared with experimental results to validate the numerical simulation. Grid independency is checked by using three different grid sizes and the validation is done by comparing the experimental results of ratio of submergence level h/c=0.95. Finally, the cambered hydrofoil NACA 2412 is analyzed to predict the free surface water waves for seven submergence ratios, ranging from submergence level h/c= 0.95 to 5.5. The pressure coefficient, velocity contour, static pressure contour, and force coefficients are shown graphically and in tabular form for Froude number 0.57. The restricted and shallow water effects are also studied in this research. This study reveals that implicit finite volume method can predict the wave of free surface due to flow past cambered hydrofoil satisfactorily. [ABSTRACT FROM AUTHOR]

Drag is a major concern in microfluidic devices impacting flow stability, energy efficiency, and fluid flow control. Minimizing drag enhances performance and efficiency in various applications, such as flow stabilization microdevices, microvalves, and micropumps. Often, superhydrophobicity is utilized for drag-reduction applications. However, superhydrophobic surfaces tend to fail at higher Reynolds numbers. This paper investigates the pressure-flow characteristics of a microchannel having a superhydrophobic bottom wall with embedded air-cavities, and a deformable top membrane, both numerically and theoretically. The aim is to understand fluid flows in the deformable superhydrophobic microchannel and leverage its water-repellent property and deformability both together to reduce drag while maintaining the durability of the superhydrophobic wall. Two-way fluid–structure interaction (FSI) and unsteady volume of fluid (VOF) methods are employed for fluid–solid boundary and liquid–air interface at ridge-cavity, respectively. A novel theoretical model has been developed for the pressure-flow characteristics of a microchannel with a deformable top and superhydrophobic bottom wall. The theoretical and numerical results for pressure drop across the microchannel have shown a good agreement with a maximum deviation of 6.69%. Four distinct types of microchannels viz, smooth (S) (rigid non-textured), smooth with deformable top (SDT), smooth with superhydrophobic bottom (SSB), and smooth with superhydrophobic bottom and deformable top wall (SSBDT) have been investigated for the comparison of their pressure-flow characteristics. The Poiseuille Number (fRe) for SSBDT microchannel is found to be lowest with an average of 18.7% and a maximum of 23.5% lower than S microchannel at Re = 60. Up to 48.59% of reduction in pressure drop was observed for the SSBDT microchannel as compared to smooth (S) microchannel of the same dimensions. Furthermore, critical Reynolds Number (Recritical) (at which the air–water interface breaks and super-hydrophobicity vanishes) was found to be ~ 20% higher for the SSBDT microchannel compared to the SSB microchannel. Thus, the wall compliance in the SSBDT microchannel is found to increase the capability to sustain the super-hydrophobicity at higher Re numbers. The proposed approach for drag reduction in microchannel can be vital to enhance the efficiency and capability of numerous microdevices needing high Reynolds number flows, such as high throughput cell sorters, microvalves, and micropumps. [ABSTRACT FROM AUTHOR]

A multiphase numerical model based on the volume of fluid (VOF) method is proposed to simulate the transient, electrochemically-generated Marangoni flow in a system comprising a NaOH electrolyte and a eutectic gallium–indium (EGaIn) metal droplet. The model incorporates appropriate equations to accurately represent the transport phenomena, including flow, electric potential, and electric current density, within the entire system. The model includes the transient variation in the interfacial tension as a function of electric current density at the interface, leading to the generation of Marangoni flow and enabling the tracking of droplet shape evolution. Notably, the model successfully captures the elongation of the droplet towards the cathode, which is validated through comparison with available experimental data.

In this study, a numerical model of cavitation bubble in the narrow-gap pure Sn liquid medium was established by two-dimensional compressible multiphase flow simulation. The effects of the pressure amplitude and the gap size on the shape, size and position of the cavitation bubble were investigated. The calculation results showed that the cavitation bubble in the narrow-gap soldering seam could exist stably after experiencing two stages of the nonlinear oscillation and the near-wall oscillation with the low-amplitude ultrasound and moved directionally on the metal substrate surface. When the pressure amplitude increased or the gap size decreased, the directional motion rate of the cavitation bubble increased and the shape of the bubble was elliptical due to the confinement effect of the substrate wall. The ultrasonic degassing mechanism of the narrow-gap soldering seam under the action of exponential decay ultrasonic vibration was analyzed by comparing the fluid pressure and velocity field variations. The flow field in the center of the soldering seam vibrated stronger than that of the peripheral regions, which could promote the outward motion of the cavitation bubble. Within the calculation time of 0.002 s, the maximum horizontal motion distance of bubble in the narrow-gap soldering seam was 1.13 mm.

Fuel atomization plays an important role in premixed combustion of aero-engine. In order to improve the atomization characteristics of an aviation fuel nozzle and optimize its structural parameters, the volume of fluid (VOF) interface capture algorithm and orthogonal experimental design were used to study the influence of internal flow and structural parameters (expansion angle, length of straight section, rise angle of swirl groove, and number of swirl groove) on the atomization characteristics. The results show that the local vortex on the swirl groove affects the fuel flow in the nozzle, and the local pressure loss can be eliminated by changing the structure of the swirl groove inlet. The number of swirl grooves has the most significant effect on Sauter mean diameter (SMD), the expansion angle is the biggest factor affecting the atomization cone angle, there is an optimal swirl groove elevation angle to minimize the oil film thickness, and the length of straight section has relatively little effect on the atomization characteristics. When the expansion angle is 60°, the length of straight section is 0.25 mm, the rising angle of swirl groove is 45°, the number of swirl grooves is 2, and the optimization effect is the best. After optimization, the oil film thickness decreases by 43.68%, the atomization cone angle increases by 3.70%, and the SMD decreases by 14.79%.

Heat pipes are a popular choice for many industries and research applications to extract heat effectively by maintaining desired device/location at almost isothermal conditions. Pulsating heat pipes, also known as wickless heat pipes, transfers the heat mainly by pumping phenomenon caused by the phase change which set the pulsating vapor-fluid motion. The evaluation of fluid flow and heat transfer characteristics inside the pulsating heat pipe is complex and challenging due to the oscillating two-phase flow between the heat source and heat sink sections. In this paper, a numerical investigation of the closed-loop pulsating heat pipe is performed to study the fluid flow dynamics and evaluate its thermal characteristics. The volume of fluid method is employed to numerically simulate the two-phase unsteady incompressible flow inside the pulsating heat pipe. The heat pipe tube has a 2 mm inside diameter filled with methanol as a working fluid at a preset pressure. The thermal performance of pulsating heat pipe is evaluated for various heat pipe filling ratios (50%, 65%, and 75%) where heat input loads of 5 − 15 W are supplied at the evaporator end for each filling ratio case. The thermal characteristics of the pulsating heat pipe are presented in terms of the thermal resistance, heat transfer coefficient, and effective thermal conductivity, whereas fluid flow dynamics are presented as flow patterns produced inside pulsating heat pipe. The numerical simulations are compared and validated with experimental results. From the present numerical and experimental study, a filling ratio of 65% is an optimized charge quality for the current configuration of the pulsating heat pipe. [ABSTRACT FROM AUTHOR]

Selective laser melting (SLM) is one of the most promising technologies in metal powder additive manufacturing. Over the past few decades, high-fidelity thermo-fluid simulations have been extensively used to understand the physical mechanisms of the SLM process. However, there are few existing simulation frameworks that can accurately reproduce the complex interactions between laser beams and powder particles, which significantly contribute to the energy flux during the whole manufacturing process. In this work, a high-fidelity, multiphase multi-physics simulation framework with the ray tracing heat source model is developed to better simulate the laser-matter interactions and melt pool dynamics during SLM. In this simulation framework, the gas-metal interface is captured by a sharp surface capturing technique (isoAdvector) and modeled by a geometrical surface reconstruction step. With the incorporation of a ray tracing heat source, the discretized laser rays can impinge on the reconstructed gas-metal interfaces and undergo multiple reflections. Moreover, simulations with ray tracing heat source and Gaussian surface heat source dealing with different structures were performed and compared. We show that the structures with more sheltered surfaces (by adjacent structures) or larger self-shielding degrees will lead to larger discrepancies between the simulation results with these two heat source models. Such observations can guide the choice of heat source models when modeling structures with different complexities. [ABSTRACT FROM AUTHOR]

This study presents computational fluid dynamics (CFD) analysis of the effects of wettability, viscosity and interfacial tension (IFT) for enhanced oil recovery (EOR) with varying pore configuration. A more realistic pore-throat geometry is studied which was motivated by oil-containing rock configuration that indicates the importance of pore geometry in EOR. The results are compared with those obtained for a simple geometry. Both saturated and unsaturated conditions are considered while the IFT varies. For both geometries, the saturated condition presents 99% of oil recovery, for the water-wet and intermediate states while it is about 88% for the oil-wet state. However, there is a significant difference in the temporal evolution of the oil recovery factor, as the complex model is 1.4 to 3 times slower than the simplified one to achieve maximum oil recovery factor under the same conditions. For unsaturated conditions, two different initial oil volumes were considered to explore the combined effect of low IFT and change in wettability. Similarly, the oil recovery process is significantly slower for the complex geometric configuration. The study of very low IFT values (10, 35, 65 and 75 µN/m) for the complex configuration in the unsaturated oil condition revealed that highest oil recovery is achieved at the IFT of 75 µN/m. The results confirm that geometric configuration plays an important role in EOR. The impact of pore structure becomes more significant in the unsaturated oil state demonstrating that very low values of IFT slow the oil recovery process. [ABSTRACT FROM AUTHOR]

This study employs numerical analysis to investigate the behavior of the National Advisory Committee for Aeronautics (NACA)66 modified (mod) hydrofoil under plunging motion, considering various cavitation numbers. The Large Eddy Simulation (LES) method is utilized to model turbulence. The hydrofoil's plunging motion leads to an increase in lift force and a decrease in drag force. Our research indicates that increasing the speed of the hydrofoil's heaving motion delays the onset of cavitation and enhances the formation of cavity clouds. Furthermore, during the peak oscillatory motion of the hydrofoil in the plunging phase, the detachment length of cavitation bubbles decreases. Additional investigations reveal that cavitation on the hydrofoil's surface accelerates the transition from a laminar to a turbulent boundary layer, strengthening the turbulent boundary layer and postponing the onset of flow separation. This research involves an in-depth investigation of the terms in the vorticity transport equation in cavitation inception, finding a correlation between vapor volume fraction and vorticity dilatation near the hydrofoil surface. This correlation proves crucial to the initial stages of the cavitation inception process. • The plunging motion of NACA66 mod hydrofoil boosts lift and cuts drag, enhancing aerodynamic efficiency. • Higher speeds in hydrofoil heaving delay cavitation onset, improving cavity cloud formation. • The study reveals a key link between vapor volume fraction and vorticity dilatation, crucial for understanding early cavitation inception. [ABSTRACT FROM AUTHOR]

The filling stage in injection/infusion moulding processes plays a key role in composite manufacturing that can be influenced by the inlet and vent ports. This will affect the production of void-free parts and the desirable process time. Flow control is usually required in experiments to optimise such a stage; however, numerical simulations can be alternatively used to predict manufacturing-induced deficiencies and potentially remove them in the actual experiments. This study uses ANSYS Fluent software to model flow-front advancement during the impregnation of woven fabrics. A developed technique is applied by creating tracking points (e.g., on-line monitor) in the direction of the flow to report/collect data for flow-front positions as a function of time. The study adopts the FVM-VOF-based two-phase flow model together with an implicit time-stepping scheme, i.e., a dual-time formulation solution method with a preconditioned pseudo-time derivative. Initially, three time-step sizes, 5 s (small), 25 s, and 50 s (large), are evaluated to examine their impact on numerical saturation lines at various fabric porosities, 40%, 50%, and 60%, for a two-dimensional (2D) rectangular mould, and predictions are then compared with the well-known analytical Darcy. This is followed by a three-dimensional (3D) curved mould for a fillet L-shaped structure, wherein the degree-of-curvature of fibre preforms is incorporated using a User-Defined Function (UDF) to tailor the impregnation process. The developed approach shows its validation (1–5.7%) with theoretical calculations and experimental data for 2D and 3D cases, respectively. The results also stress that a shorter computational time can be achieved with a large time-step size while maintaining the same level of accuracy. [ABSTRACT FROM AUTHOR]

This study ascertains a three-dimensional (3D) numerical modeling employing hybrid conical-cylindrical heat source concerning the heat transfer, molten fluid flow weld pool dynamics, and cooling rate phenomena associated with the laser weld pool of 316 LN stainless steel (SS) by computational fluid dynamics. The heat source interprets the transmission of laser energy to the substrate by accounting for recoil pressure and surface tension effect using the multiphase flow modeling. The impact of laser power for a constant welding speed on the penetration depth is predicted to select an optimized laser energy input to carry out full penetration laser welding experiment. The model pictures the depth of penetration, temperature distribution, velocity field, and weld pool flow pattern and keyhole behavior for the optimized welding condition. Non-dimensional heat transfer entities such as Peclet and Marangoni numbers are also assessed that provide insight related to the thermal-fluid flow mechanism and final weld fusion zone attributes of the 316 LN SS laser weld. The simulated model agrees well with the experimentally achieved full penetration laser weld giving fair concordance with the weld bead dimensions and thermocouple measurements. The model has been used to calculate the secondary dendritic arm spacing in the fusion zone. Calculated values were in agreement with the measured values. The numerical outcomes recognize that the hybrid conical-cylindrical heat source model is well suited for predicting weld peak temperature, weld pool velocity, weld pool dynamics, weld pool shape, and cooling rate for the laser welding of 316 LN SS. [ABSTRACT FROM AUTHOR]

In the urban water cycle, adsorption facilitated by engineered granular media increasingly is deployed for solute separation in potable water, stormwater, and wastewater systems. Of these systems, stormwater treatment is inordinately complex. Stormwater systems are passive, decentralized, and subject to highly unsteady and uncontrolled fluxes with multiphase interactions. This study proposes a multiphase and multiphysics computational fluid dynamics (CFD) model, interAdsFoam, to simulate turbulence mixing and adsorption with dynamic water–air interface and reaction zones. An original CFD model is proposed, benchmarked, and validated with data sets across a range of scales: (1) bench-scale columns for model parameter estimation, (2) physical modeling of a radial flow adsorption reactor (RFR) subject to controlled fluxes, and (3) field monitoring of a commercial volumetric radial flow adsorption reactor (VRFR) system subject to uncontrolled event-based fluxes. The results illustrate (1) the nonuniqueness of numerical solutions for parameter estimation in adsorption modeling; (2) that regulating the parameter estimation process with isotherms improves model generalizability; (3) inverse modeling of the RFR hydraulic resistance with the quadratic Thiem model can provide a more accurate representation than the Ergun model; and (4) that turbulence transport and chemical adsorption are dynamically coupled with the air–water momentum balance. The proposed CFD model predicts total dissolved phosphorus (TDP) transport and fate based on field monitoring of the VRFR. System dynamics and treatment functionality are elucidated, and implications for practical reactor design are discussed. The proposed open-source CFD model provides a novel framework for higher-fidelity urban water adsorption reactor simulation, design, and optimization than current methods for adsorption. [ABSTRACT FROM AUTHOR]

The surface areas of the materials are generally the most vulnerable parts since they are directly exposed to different stresses such as wear, fatigue, and corrosion. On the other hand, the successive impact of the droplets finds numerous applications in additive manufacturing technologies such as 3D printing and liquid metal projection. The lamella state formed by the impact and spreading of the first particle represents the target for the second; however, its molten state or fragmented state, bouncing or a slide, interacts thermally and dynamically to allow or not allow stacking. The deposition, deformation, and solidification of the droplets are the constituent steps of the process which determine the final result, as the topography of the substrate not only conditions the mechanical adhesion of the drop to the substrate but also affects the wettability of the surfaces. The objective of this work was to model by numerical simulation the impact of successive and simultaneous droplets with solidification and simultaneous deformation in the presence of an oxide layer on the substrate, which presents different topography, in order to fix the knowledge on the behavior of the impact, the spreading, or the splashing with solidification. However, a peak diameter greater than 5% of the particle diameter causes the formation of concave roughness which directly infects the mechanical adhering and subsequently the formation of an ordinary lamella. [ABSTRACT FROM AUTHOR]

A volume of fluid computational fluid dynamics (VOF-CFD) model was used to investigate hydrodynamics of air-water bubble columns in the gas distributor region under bubbling, transient, and jetting flow regimes. The Reynolds-averaged Navier-Stokes (RANS) and large eddy simulation (LES) turbulence equations were coupled with the VOF-CFisms@2015D model. A novel bubble detection algorithm was developed to calculate the bubble size, where a gas fraction of 0.5 was adopted to detect bubbles in the gas-liquid mixture. The CFD results for all three flow regimes were compared to the experimental data in terms of the bubble size distribution (BSD) and mean bubble size. In the framework of VOF, the LES turbulence model captured bubble behaviors in the three flow regimes more accurately than the RANS approach by taking computational time 20% more. Increasing the surface tension from 0.025 to 0.0719 N/m resulted in the increment of the Sauter mean diameter from 4.0 to 5.4 mm. The VOF-CFD model coupled with LES yielded the initial BSD near the gas distributor, which is necessary for Eulerian CFD often applied to an entire column. [Display omitted] • A VOF-CFD model was used to predict the initial bubble size in bubble columns. • A bubble detecting algorithm was proposed to identify the bubble size distribution. • The VOF-CFD model with large eddy simulation (LES) well captured bubble behaviors. • The VOF-CFD with LES providing the initial bubble size is beneficial to Eulerian CFD. [ABSTRACT FROM AUTHOR]

Microreactors have emerged as a viable option to perform mass transfer limited gas-liquid reactions due to the advantage of high gas-liquid interfacial area density. Slug and annular flow regimes are the two most commonly preferred flow regimes to perform reactions in microreactors. In the annular flow regime, characterized by a continuous gas core and an annular liquid film on the wall, waves are observed at the interface between the two phases. The characteristics of these waves depend on the properties of the fluids and their flow rates. In this work, the hydrodynamics of axisymmetric gas-liquid annular flow in millimeter-size channels is investigated computationally employing volume of fluid method in OpenFOAM solver. CFD simulations have been performed for nitrogen-water and nitrogen-water and ethylene glycol mixture over a range of gas and liquid flow rates. Depending on the gas and liquid flow rates and liquid viscosity, coalescing and non-coalescing waves are observed at the interface. The properties of the interfacial waves such as frequency, wave spacing and wave velocity are determined using spatiotemporal analysis and the effect of gas and liquid flow rates on the wave characteristics is investigated. Further, the time-averaged pressure gradient and interfacial shear stress are reported. [Display omitted] • Axisymmetric modeling of gas-liquid annular flow in microchannels. • Volume of fluid (VOF) method using OpenFOAM solver. • Wave characterization using spatiotemporal analysis. • Large amplitude coalescing and non-coalescing waves observed at the interface. • Wave spacing reduces with increasing liquid mass flow rate. • Expression for the interfacial shear stress is obtained. [ABSTRACT FROM AUTHOR]

In this study, the primary breakup of a high-speed diesel jet is investigated using a CFD methodology that combines an LES model with a VOF technique for free surface capture. Inner-nozzle turbulence and cavitation are simplified as the sinusoidal radial velocity with a given amplitude and frequency. The ligament and droplet formation process are captured, the liquid jet is disturbed by the radial velocity, and umbrella-shaped crests are created. Meanwhile, ligaments are formed from the edges of crests because of shear stress and surface tension. We investigate the effect on the characteristics of the surface wave and the liquid structure of different disturbance frequencies and amplitudes. The variation in the disturbance amplitude and frequency facilitates the formation of a variety of liquid structures, such as waves, upstream/downstream-directed bells, and droplet chains. Increasing the disturbance frequency reduces the growth rate of the surface waves of the liquid jet. With an increase in disturbance amplitude, the amplitude of surface waves evidently increases. Furthermore, as the disturbance frequency and amplitude increase, the thickness and Weber number of the radial liquid sheet decrease, and this causes the ligament diameter of the primary breakup to become small. Finally, the primary breakup time is investigated, and the time scale of the liquid jet primary breakup decreases as the disturbance amplitude increases, which indicates that an increase in the disturbance amplitude promotes the atomization of a disturbed liquid jet. [ABSTRACT FROM AUTHOR]

This study predicts how the Free Surface Level (FSL) variations around finite length vegetation affect flow structure by using a numerical simulation. The volume of fluid (VOF) technique with the Reynolds stress model (RSM) was used for the simulation. Multizone Hexahedral meshing was adopted to accurately track the free surface level with minimum numerical diffusion at the water–air interface. After the validation, finite length emergent vegetation patches were selected based on the aspect ratio (AR = vegetation width-length ratio) under constant subcritical flow conditions for an inland tsunami flow. The results showed that the generation of large vortices was predominated in wider vegetation patches (AR > 1) due to the increase and decrease in the FSL at the front and back of the vegetation compared to longer vegetation patches (AR ≤ 1), as this offered more resistance against the approaching flow. The wider vegetation patches (AR > 1) are favorable in terms of generating a large area of low velocity compared to the longer vegetation patch (AR < 1) directly downstream of the vegetation patch. On the other hand, it has a negative impact on the adjacent downstream gap region, where a 14.3–34.9% increase in velocity was observed. The longer vegetation patches (AR < 1) generate optimal conditions within the vegetation region due to great velocity reduction. Moreover, in all the AR vegetation cases, the water turbulent intensity was maximum in the vegetation region compared to the adjacent gap region and air turbulent intensity above the FSL, suggesting strong air entrainment over this region. The results of this study are important in constructing vegetation layouts based on the AR of the vegetation for tsunami mitigation. [ABSTRACT FROM AUTHOR]

Due to various engineering applications, spontaneous bubble movement on the heated surface has brought huge attention. This work numerically studied the bubble migration driven by the thermo-capillary force under the temperature gradients perpendicular to the gravity direction. This problem is constructed in a two-dimensional domain, and the volume of fluid (VOF) method is adopted to capture the properties of the bubble interface between the vapor and the liquid. One still vapor bubble is initially positioned at the center of the liquid domain, and the temperature gradient is applied to two side walls. The results show that the bubble with a size greater than the capillary length can only oscillate near the initial position even with a larger temperature gradient. The deformation of the bubble such as spheroid and spherical cap can be found around this regime. However, the movement of the bubble with a size smaller than the capillary length is significant under a higher temperature gradient, and it remains a spherical shape. The coefficient of thermo-capillary force (CTh) is defined within this work, and it is found that a larger Weber number ( W e ) accomplishes a larger CTh. This work may provide more precise guidance for smart bubble manipulation and critical heat flux estimation for future nuclear reactor design. [ABSTRACT FROM AUTHOR]

Wire-mesh sensors (WMSs) have been used to measure various characteristics of bubbles, such as volume fraction, size and velocity. The WMS used in this study consists of a grid of nine by nine wires arranged in an orthogonal shape. Transmitter wires are activated sequentially and receiver wires pick up the electric signals and convert them to a current. Multiphase flow, the electric conductivity of each phase, allows characteristic electrical signals to flow and from this information the volume fraction can be calculated. However, deformation of bubbles and the intrusive effects of wires have yet to be considered. To address these issues, we conducted numerical simulations using commercial software. The actual behavior of a single bubble was considered to calculate the electrostatic and two-phase flow simultaneously. First, a bubble was considered stationary in a spherical shape at the center of the WMS. A user-defined function was used to calculate the governing equation of the electric field and then activate electric signals on the transmitter wires. The numerical results were compared with reference values, and the error of a volume fraction was quantified. After that, we considered a bubble rising without a change of shape in the pseudo-dynamic process. However, for the dynamic process, a volume of fluid model was added and a bubble interface that reflects its actual movement was considered. A comparison between the pseudo-dynamic and dynamic processes was conducted using the same positional relations between the wire and bubble surface. When the bubble contacted with and then separated from the wire, differences in the received signal and an overshooting phenomenon were observed owing to deformation of the bubble. Also, the range of locations where the bubble would begin to affect the electric field because of the flattened shape of the bubble was observed.

The present paper aims to evaluate the local scouring of non-cohesive sediment beds consisted of uniform sediment particles downstream of a D - type piano key weir in steady flow condition. The experiments were conducted for one model of D - type piano key weir with five keys. Accordingly, the effect of hydraulic parameters was examined on scouring profiles and depth, downstream of the piano key weir. While nine runs were conducted to evaluate the local scouring downstream of the piano key weir under clear-water conditions with different discharge rates and tail water depths. The experimental results showed that the maximum scouring depth increased with increasing the discharge. Further, increasing the tail water depth resulted in decreasing the largest scour depth. The 3D numerical simulation was implemented using a CFD package. Overall, the results of the numerical modelling were in agreement with the experimental data. [ABSTRACT FROM AUTHOR]

Wire-mesh sensors (WMSs) have been used to measure various characteristics of bubbles, such as volume fraction, size and velocity. The WMS used in this study consists of a grid of nine by nine wires arranged in an orthogonal shape. Transmitter wires are activated sequentially and receiver wires pick up the electric signals and convert them to a current. Multiphase flow, the electric conductivity of each phase, allows characteristic electrical signals to flow and from this information the volume fraction can be calculated. However, deformation of bubbles and the intrusive effects of wires have yet to be considered. To address these issues, we conducted numerical simulations using commercial software. The actual behavior of a single bubble was considered to calculate the electrostatic and two-phase flow simultaneously. First, a bubble was considered stationary in a spherical shape at the center of the WMS. A user-defined function was used to calculate the governing equation of the electric field and then activate electric signals on the transmitter wires. The numerical results were compared with reference values, and the error of a volume fraction was quantified. After that, we considered a bubble rising without a change of shape in the pseudo-dynamic process. However, for the dynamic process, a volume of fluid model was added and a bubble interface that reflects its actual movement was considered. A comparison between the pseudo-dynamic and dynamic processes was conducted using the same positional relations between the wire and bubble surface. When the bubble contacted with and then separated from the wire, differences in the received signal and an overshooting phenomenon were observed owing to deformation of the bubble. Also, the range of locations where the bubble would begin to affect the electric field because of the flattened shape of the bubble was observed. [ABSTRACT FROM AUTHOR]

Dam break analysis plays a key role in hydraulics engineering for safety. In this paper, 3D numerical simulations of dam-break flow using Finite Volume and Lattice Boltzmann methods are studied and discussed. All the computation in this work is achieved by ANSYS Fluent and XFlow. Large Eddy Simulation (LES) is employed as the turbulence model and the free surface flow is captured using a Volume of Fluid (VOF) model in the two simulation approaches. Results are then compared with experimental data on dam-break flow through complex obstacles. This experimental data is obtained by a high-speed camera aiming to capture free surface waves. The comparison between the experimental data and simulations shows good tendency. However, LBM requires less computational time.

The present study was executed to compare flow parameters of submerged jump under gate using physical and numerical models. Twenty experimental runs were carried out to study the impact of spaced corrugated beds on basic characteristics of submerged hydraulic jump for values of Froude numbers were ranging from 1.5 to 9.5. Experiments were conducted also for smooth bed. Submerged jump on best spaced corrugated bed depending on experimental runs was simulated by using VOF method in FLUNET Software and k-ε and RNG k-ε turbulent models are used. To simulate a highly transient and turbulent flow conditions a free surface CFD numerical model has been applied. The results revealed that there is a great coincide between experimental and numerical simulation, corrugated beds reduced jump length and sequent depth by average 5.69% and 12.96% respectively, k-ε and RNG k-ε turbulence models have the ability to simulate this phenomenon and finally the RNG k-ε model give results more consistent with laboratory experiments.

The effect of varying vortex settling basin (VSB) outlet configurations on the removal of sediment particles >75 μm was computationally investigated using ANSYS Fluent's Euler-Lagrange approach, which incorporated supervised optimization and was validated by physical modeling. A rectangular centroidal outlet was established with a low outlet weir and a shaft with the following dimensions: length equal to it 1.28* Inlet diameter, breadth equal to inlet diameter, and height equal to inlet diameter located 180° opposite the inlet. The shaft was designed for partially full conditions. A low weir height with less than the submergence depth is recommended at small river abstraction works (<100 L·s−1). [ABSTRACT FROM AUTHOR]

The process of oil-water displacement is one of the key technologies in offshore underwater tank. When hot oil is contacting the normal-temperature water, the interfacial heat transfer should be investigated as the heat loss may result in wax precipitation and solidification which will reduce the flowing of oil and thus affect the process. As for the numerical simulation of heat transfer, the calculation is costly as the underwater tank is usually large and the displacement period is long. A high precision computing method would greatly reduce the mesh scale. Therefore, this research is performed to establish a high precision computing solver. Based on volume of fluid (VOF), a new form of energy equation is proposed. This equation is derived from temperature equation and the variable internal energy per volume is used. This variable is additive and has a close relationship with volume fraction. With algorithm implantation to OpenFOAM, two non-isothermal VOF solvers are established corresponding to temperature equation and the new equation respectively. After an analytical solution is built, the two solvers are compared. The solver based on the new equation presents far more accurate results than the solver based on temperature equation. An energy weighted scheme is more reasonable than a linear temperature distribution for the mixture phase. [ABSTRACT FROM AUTHOR]

Recently, the trend towards sustainable energy production and pollution control has motivated the increased consumption of ultra-low-sulfur diesel (ULSD) or bio-fuels. Such fuels have relatively low surface tension with water and therefore, the separation of water from fuel has become a challenging problem. The separation process relies on using porous structures for the collection and removal of water droplets. Hence, understanding the interaction between water droplets and the separators is vital. The simplest geometry of a separator is the wire mesh screen, which is used in many modern water–diesel separators. Thus, it is considered here for systematic study. In this work, pore-scale computational fluid dynamics (CFD) simulations were performed using OpenFOAM® (an open-source C++ toolbox for fluid dynamics simulations) coupled with a new accurate scheme for the computation of the surface tension force. First, two validation test cases were performed and compared to experimental observations in corresponding bubble-point tests. Second, in order to describe the interaction between water droplets and wire mesh screens, the simulations were performed with different parameters: mean diesel velocity, open area ratio, fiber radii, Young–Laplace contact angle, and the droplet radius. New correlations were obtained which describe the average reduction of open surface area (clogging), the pressure drop, and retention criteria. [ABSTRACT FROM AUTHOR]

The filling stage in injection/infusion moulding processes plays a key role in composite manufacturing that can be influenced by the inlet and vent ports. This will affect the production of void-free parts and the desirable process time. Flow control is usually required in experiments to optimise such a stage; however, numerical simulations can be alternatively used to predict manufacturing-induced deficiencies and potentially remove them in the actual experiments. This study uses ANSYS Fluent software to model flow-front advancement during the impregnation of woven fabrics. A developed technique is applied by creating tracking points (e.g., on-line monitor) in the direction of the flow to report/collect data for flow-front positions as a function of time. The study adopts the FVM-VOF-based two-phase flow model together with an implicit time-stepping scheme, i.e., a dual-time formulation solution method with a preconditioned pseudo-time derivative. Initially, three time-step sizes, 5 s (small), 25 s, and 50 s (large), are evaluated to examine their impact on numerical saturation lines at various fabric porosities, 40%, 50%, and 60%, for a two-dimensional (2D) rectangular mould, and predictions are then compared with the well-known analytical Darcy. This is followed by a three-dimensional (3D) curved mould for a fillet L-shaped structure, wherein the degree-of-curvature of fibre preforms is incorporated using a User-Defined Function (UDF) to tailor the impregnation process. The developed approach shows its validation (1–5.7%) with theoretical calculations and experimental data for 2D and 3D cases, respectively. The results also stress that a shorter computational time can be achieved with a large time-step size while maintaining the same level of accuracy.

• Proposed an empirical primary atomization model considering the aerodynamic effect along with the turbulence effect. • Analyzed the flow characteristics of liquid jet in crossflow and its influence on the droplets distribution. • Assessed the empirical constants in the model and found the most appropriate value for this work. • Compared the droplets properties at different Weber number. The hybrid Eulerian-Lagrangian approach is used to simulate the atomization process of spray jet in subsonic crossflow. A coupled Volume of Fluid (VOF) - Lagrangian Particle Tracking (LPT) solver is implemented in the open-source platform OpenFOAM to solve the governing equations for the continuous and discrete phase respectively. An empirical model for primary atomization is proposed, in which the aerodynamic effect is taken into account, along with the turbulence effect. Thus, it is suitable for the flow at a low liquid-gas density ratio, i.e., less than 500. The performance of the presented model is evaluated and verified by comparisons of the simulated results with the experimental data. The flow characteristics of flow fields and distribution of droplet diameters are analyzed in detail. It is revealed that the vortex structures have a direct impact on the distribution of the droplets. The effects of the empirical constants in the atomization model are also examined. Finally, it is shown that the model performs better for the flow at a higher Weber number, in which the aerodynamic effect is more significant. [Display omitted] [ABSTRACT FROM AUTHOR]

A method is proposed to investigate the steady deformation and the drag of a single droplet in a flowing gas at a high Reynolds number. The volume of fluid (VOF) method is used to model the droplet surface structure. The direct numerical simulation (DNS) method is used to model the gas flow field. In order to avoid the effect of the droplet acceleration on the drag and reduce the computation cost, a body force is added to the droplet to make it fixed at a constant position. The body force is determined by using the Newton iteration procedure. The simulated droplet aspect ratio and the drag coefficient agree well with the published experimental data. Meanwhile, the sources of the drag are analyzed and the effect of the Reynolds number and the Weber numbers on the droplet deformation and the drag are studied. The drag mainly comes from the pressure difference between the droplet-leading zone and the trailing zone, and the turbulence wake would increase the drag. [ABSTRACT FROM AUTHOR]

This paper presents an experimental and numerical study of gas-liquid annular flow in horizontal 180 U-bends. The paper aims to study the effect of bend curvature radius and superficial gas velocity in the liquid film's behavior and annular flow characteristics. The study is divided into three sections. The first section corresponds to the experimental methodology and results. The second section compresses the validation of the computational fluid dynamic (CFD) model with the experimental results. Finally, the last section presents the CFD estimation of additional variables that cannot be acquired with the existing experimental setup. The experimental results provide an initial understanding of the multiphase mixture obtained using optical techniques (i.e., High-Speed Filming (HSF) analysis). The comparison between the experiments and the numerical simulations is presented, and a reasonable agreement is observed between both approaches. Finally, additional results such as film distribution and rotation before and after the bend are extracted from the CFD simulations.

Due to various engineering applications, spontaneous bubble movement on the heated surface has brought huge attention. This work numerically studied the bubble migration driven by the thermo-capillary force under the temperature gradients perpendicular to the gravity direction. This problem is constructed in a two-dimensional domain, and the volume of fluid (VOF) method is adopted to capture the properties of the bubble interface between the vapor and the liquid. One still vapor bubble is initially positioned at the center of the liquid domain, and the temperature gradient is applied to two side walls. The results show that the bubble with a size greater than the capillary length can only oscillate near the initial position even with a larger temperature gradient. The deformation of the bubble such as spheroid and spherical cap can be found around this regime. However, the movement of the bubble with a size smaller than the capillary length is significant under a higher temperature gradient, and it remains a spherical shape. The coefficient of thermo-capillary force (CTh) is defined within this work, and it is found that a larger Weber number (We) accomplishes a larger CTh. This work may provide more precise guidance for smart bubble manipulation and critical heat flux estimation for future nuclear reactor design.