We propose a hybrid continuum surface tension force (CSF) formulation to model the interface interaction within the three-phase volume of fluid (VOF) method. Instead of employing the height function ...globally, we compute the curvature based on a smooth fraction function near the region of the triple contact point. In addition, we apply the isotropic finite difference method to calculate derivatives, and the current scheme readily accommodates adaptive mesh refinement, greatly enhancing efficiency. We rigorously validate the hybrid CSF using two benchmark problems that have received limited attention in previous studies of the three-phase VOF method. Using the hybrid CSF method, we accurately predict the behavior of a liquid lens under specific surface tension ratios. Furthermore, the simulation results of the equilibrium morphology of two contacting droplets are consistent with the theoretical expectations.
•Hybrid continuum surface tension force.•Three-dimensional and three-phase VOF method.•Benchmark validations for three-phase VOF method.
•We implement and validate a RANS–VOF model of an OWC wave energy converter.•We study the OWC performances for different wave conditions and damping values.•Damping is the main factor of OWC ...performances, closely followed by period.•There is an optimum damping for each wave condition.•We develop a procedure to determine the optimum turbine-chamber coupling.
The performance of an oscillating water column (OWC) wave energy converter depends on many factors, among which the incident wave conditions, the tidal level or the coupling between the chamber and the air turbine. In this work a 2D numerical model based on the RANS equations and the VOF surface capturing scheme (RANS–VOF) is implemented in order to study the optimum turbine-chamber coupling for a given OWC. The model represents a numerical wave flume where the OWC is tested under regular and irregular waves and for different damping coefficients, i.e., turbines of different characteristics. First, the numerical model is validated under regular and irregular waves using results from physical model tests. Excellent agreement is obtained between both models, physical and numerical. After the validation, an extensive campaign of computational tests is carried out, studying the performance of the OWC under nine different damping coefficients. The model developed allows, first, to quantify the relevance of the damping coefficient and wave conditions on the performance of an OWC chamber; and second, to define the damping condition which maximizes that performance, determining the characteristics that a turbine must meet to achieve the optimum coupling. In this manner this work contributes to the development of high performance OWCs.
•The paper presents the effects of water on obstacles in the dam break flow problem are investigated numerically.•It is solved by the Navier–Stokes and multiphase flow equations for incompressible ...fluid.•The numerical solution based on the PISO algorithm (Pressure-Implicit with Splitting of Operators).•Various forms of obstacles were examined, by which the pressure distributions were reduced three times on the dam surface.
In this paper, the effects of water on obstacles in the dam break flow problem are investigated numerically. The numerical method is based on the Navier–Stokes equations describing the flow of an incompressible viscous fluid and the equation for the phase. As a numerical method for solving equations, the numerical algorithm PISO (Pressure-Implicit with Splitting of Operators) was chosen. The water surface movement is captured by using the volume of fluid (VOF) method, which leads to a strict mass conservation. Moreover the accuracy and reliability of the 2D and 3D models were tested using several small and large-scale laboratory experiments on dam destruction problem. The obtained free surface dynamics was compared with the experimental data and numerical results of other authors. These numerical results gave good agreement with the experimental data. Comparison of simulation results with experimental data for various turbulent models was also performed. By dam break flow problem simulation, the best turbulent models were chosen, which describe almost the same pressure distribution as in the experiment. Finally, various forms of obstacles were examined, by which the pressure distributions were reduced three times on the dam surface.
This research aims to further understand the CO2 flow behavior during CO2 flooding. Here, we used NMR to monitor oil saturation during core flooding experiments and volume of fluid method to ...calculate CO2 displacement during simulation. The results indicate that during miscible flooding, piston displacement occurred in the early stages, followed by viscous fingering. Oil was first produced from macropores, followed by micropores and micropores. However, during immiscible flooding, viscous fingering occurred and gradually intensified until CO2 breakthrough. In these tests, oil was almost exclusively produced from macropores. The VOF results showed that viscous fingering with tip splitting is predominant in immiscible flooding. Piston displacement flow prevails near the core upstream and then evolves downstream into parallel viscous fingering in miscible flooding. Furthermore, increasing viscosity leads to a transition from formation of densely distributed, parallel, viscous fingers to growth of a few discrete, well-developed, dominant fingers. Increasing of injection rate brings the CO2 flow patterns closer to parallel dense viscous fingering, which improves sweep efficiency in midstream and downstream but slightly reduced sweep efficiency in upstream. On the other hand, a strong preferential flow channel forms when dominant viscous fingering occurs, which leads to a decrease of sweep efficiency.
•Oil recovery and CO2 flow of CO2 miscible flooding and immiscible flooding were studied using VOF simulation method and NMR technology.•Increasing injection rate lead to rapid formation and merging of multiple viscous fingers, promoted the overall sweep efficiency of CO2, thereby improving oil recovery.•Increasing oil viscosity reduces the degree of miscibility, causing serious viscous fingering phenomenon.•Piston displacement near the upstream and fingering near the downstream in miscible flooding.
•Explored the characteristics of falling film spreading and heat transfer under vertical vapor.•Compared the impacts of downward and upward vapor shearing on falling film flow and heat ...transfer.•Elucidated the influencing mechanism of vertical vapor on falling film heat transfer performance.•Downward and upward vapor generally exerts effect on the upper and lower half tubes, respectively.
Falling film evaporators are commonly employed in a wide range of industrial applications, with a particular emphasis on the management of vapor generated during operations. It is widely recognized that vapor streams have a significant influence on falling film flow and heat transfer. In this paper, we conducted numerical investigations of this issue in the presence of vertical vapor streams and validated the present numerical results against previous experimental data. The results indicate that the length of the liquid tongues and the interaction time between two liquid films are affected by both downward and upward vapor streams. The effect of vertical vapor on the film thickness is dependent on the vapor’s orientation and position on the tube. Typically, is decreased by 25 % at z* = 0 and vg = 4.0 ms−1 and is increased by 20 % at z* = 0 and vg = 4.0 ms−1. The downward vapor enhances heat transfer on the top half of the tube’s periphery while weakening it on the bottom half, while the upward vapor contributes to heat transfer enhancement mainly in the detachment zone. Overall, the vertical vapor stream causes substantial redistributions of the heat transfer coefficient, velocity vector, and liquid film thickness in three distinct zones. Downward and upward vapor streams predominantly impact the upper and lower parts of the tube, respectively. Within the current velocity range, it is evident that vertical vapor streams consistently lead to an average enhancement in heat transfer.
This paper proposes volume of fluid (VOF) model to investigate the potential of Al2O3-water nanofluid to improve the productivity of a single slope solar still. Accordingly, VOF model is utilized to ...simulate the evaporation and condensation phenomena in the solar still. An entropy generation analysis is used to evaluate the system from the second law of thermodynamics viewpoint. The effects of solid volume fraction of nanofluid on the productivity and entropy generation in the solar still have been examined. The numerical results are compared with the experimental data available in the literature to benchmark the accuracy of VOF model. The numerical results showed that the productivity of solar still increases with an increase in the solid volume fraction of nanoparticles. The productivity increases about 25% as the solid volume fraction increases in the range of 0%–5%. There is about 18% enhancement in the average Nusselt number as the solid volume fraction increases in the range of 0%–5%. Moreover, the maximum values of viscous and thermal entropy generations are happened at the regions around the bottom and top surfaces of the solar still. Both types of entropy generation increase by increasing the solid volume fraction of nanoparticles. The viscous and thermal entropy generations increase about 95% and 25%, respectively as the solid volume fraction increases in the range of 0%–5%.
•Potential of nanofluid for improving the productivity of a solar still is studied.•VOF model is used to simulate the evaporation-condensation phenomena.•Productivity of still increases 25% by using nanofluid with volume fraction of 5%.•Maximum entropy generation is occurred near bottom and top surfaces of the still.•Thermal entropy generation is dominant for all considered cases in this research.
The advancement of technology has led to a significant increase in thermal loads, thus presenting new challenges in heat dissipation. Traditional single-phase cooling systems are often inadequate to ...meet these demands. As a result, phase-change technologies utilizing boiling and condensation, which can achieve high heat transfer coefficients, have garnered considerable attention. To delve into the complex physics of boiling heat transfer, researchers are increasingly turning to numerical simulation methods such as the Volume of Fluid (VOF) and the Diffuse Interface (DI) approaches. The VOF method, widely employed for macro-scale simulations ranging from micrometers to millimeters, effectively tracks bubble growth and detachment. Conversely, the DI method represents the interface as a continuous phase field and is primarily used for mesoscale simulations spanning from nanometers to micrometers. While the DI method excels in resolving mesoscale interfacial phenomena, it is computationally expensive for larger domains. Considering the strengths and weaknesses of both the VOF and DI methods, there is a growing interest in developing a multi-scale modeling approach that amalgamates their benefits. To pursue this objective, initial efforts are being made to evaluate the scaling capability of VOF towards lower spatial and temporal limits. Hence, an enhanced and customized VOF methodology has been developed within the OpenFOAM toolbox. This methodology is employed to investigate various bubble growth scenarios, progressively exploring its applicability at lower temporal and spatial scales to identify the lower limits of its application. By taking this first step towards combining the strengths of both the VOF and DI methods through a multi-scale modeling approach, the presented paper paves the way for enhancing the accuracy and efficiency of modelling approaches for boiling heat transfer while tackling a challenge associated with varying spatial and temporal scales. This endeavor not only pushes the boundaries of computational fluid dynamics but also holds promise for addressing real-world thermal management issues in diverse technological applications.
This study investigated the impact of sediment clogging on the hydraulic performance of porous asphalt (PA) pavements using a novel numerical approach combining the discrete element method (DEM) and ...computational fluid dynamics (CFD). In particular, image analysis techniques captured the morphology of real aggregates for the 3D appearance information. Then, the information was used to reproduce aggregates and their gradation in asphalt mixes using DEM, including sediments causing clogging of the PA. The samples in the DEM were transferred to CFD for hydraulic performance simulation. DEM samples were prepared with air voids content of 20% and 25%. Clogging particles with different sizes of 0.5 mm and 0.75 mm were used. The study found that clogging particles can move to deeper layers of the PA pavement but have a high potential to be trapped in upper layers and cause clogging issues in the top 5 mm and middle-to-bottom sections. Due to surface clogging, the air voids content for the 20% porosity PA sample was reduced by approximately 2% on average, whereas up to 7% reduction in air voids content was observed for the 25% PA sample. This led to 37.35% and 42.7% reduction in hydraulic permeability, respectively. The reduction in air voids content below 10 mm from the surface is negligible (0.3–0.7% reduction). Due to the clogging development inside the pore structure, the surface runoff on the top of the sample increases by 8.1% for the 20% air voids asphalt sample case and 37.5% for the 25% voids sample.
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•Urban floods generate disruptions on multiple levels to city authorities and people•Permeable road pavements reduce stormwater runoff but can be prone to clogging•3D models of clogged porous pavements are investigated via a novel methodology•DEM-made porous pavements are analysed via multi-phase CFD simulations•Clogging affects the hydraulic performance and surface runoff accumulation
One of the significant issues in hydraulic engineering is reducing erosion in rivers by using groynes to preserve soil. The purpose of this study is to investigate numerically the groynes' presence ...on the sedimentary flow parameters using FLOW-3D software. For this purpose, groynes were examined at angles 30°, 60°, and 90° under 10 scenarios in various discharge and hydraulic conditions. Here, the mesh block with dimensions of 5 mm was chosen as the optimal mesh block for simulating models. In addition, Large Eddy Simulation (LES) turbulence model was used for simulations. In the scenarios where two blades are used scouring is observed in the first blade, while the sedimentation phenomenon was observed in the groyne after the first groyne in the direction of the flow. In the two blades with a distance of 0.60 m from each other, 48 mm erosion occurred. The highest amount of scour is related to the arched groyne (LLeft-Q285) with 45 mm. Discharges have an increased effect on scouring, so by comparing the scenarios with one groyne (I-Q285, I-Q200, and I-Q350), the lowest amount is with the value of 5.5mm corresponding to I-Q200. The insufficient erosion in the angled groynes corresponds to the smaller angle scenario.
•Interactions of a coaxial bubble pair in liquid metal have been performed.•Influence mechanism of magnetic field and wall on bubbles coalescence was revealed.•Attractive force of wake effect acting ...on tailing bubble is reduced by MHD effect.•Coalescence time of bubble pair is dependent to wall confinement ratio Cr and Ha.
The motion and coalescence of a coaxial bubble pair rising in a liquid metal column under horizontal magnetic fields were numerically examined using the VOF method in this present paper. The MHD (Magnetohydrodynamics) effects on the characteristics of rise velocity, flow field, and coalescence process of bubble pair by considering various wall confinement ratios (Cr) were analyzed. The results indicate that the effects of magnetic field and wall confinement on the coalescence of the coaxial bubbles are non-monotonic. For smaller Cr, a higher initial rise velocity of the bubbles is generated by strengthening the counter-rotating toroidal vortices around bubbles in the initial stage, but the terminal rise velocity decreases in the stable stage. In the presence of the magnetic field, both the initial rise velocity and terminal rise velocity decrease. A horizontal magnetic field makes the flow field around the bubbles be anisotropic by weakening the toroidal vortices on both sides of the bubbles along the magnetic field direction, which also dampens the wake vortices of the leading bubble and thus reduces the attractive force of wake effect acting on the tailing bubble. On the other hand, the downward Lorentz force induced by the magnetic field on the top of the leading bubble suppresses its upward motion, which makes the tailing bubble collide with the leading bubble earlier. As the competition between the above two mechanisms varies with the magnetic field strength, the coalescence time of the bubble pair also changes accordingly. Particularly, a strong horizontal magnetic field tends to promote the bubbles coalescence under the wall effects and delay that when the wall effects are minor or negligible. For Ha=771, bubbles coalescence at Cr=2 is about 32 % earlier than that at Cr=4.
