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.
This study introduces a comprehensive numerical model capable of simulating the evaporation of suspended droplets under different gravity conditions. Unlike previous studies, this work provides a ...detailed description of the multicomponent evaporation process by integrating: (i) interface-resolved evaporation; (ii) suspension by the action of the surface tension force, and (iii) variable physical properties. The model effectively captures complex phenomena such as thermal expansion, natural convective fluxes, and liquid internal recirculation, which cannot be directly resolved using more widespread spherically-symmetric models. Validation against experimental data confirms the model’s accuracy in predicting the droplet evaporation dynamics, and its utility in resolving discrepancies between prior numerical simulations results and experimental data. The model was implemented in the Basilisk framework; both the code and the simulations setups are freely available on the Basilisk sandbox.
•Numerical model for the evaporation of suspended droplets with variable properties.•Accurate droplet suspension strategy for simulations in any gravity condition.•Demonstrating the effect of residual gravity on the experimental data.•Good agreement between the model’s results and experiments in normal gravity.
•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.
•Direct pore-scale modelling of two-phase flow in three-dimensional porous media by VOF method.•The evolution of remaining oil was investigated by considering wettability, viscous force and capillary ...number.•Phase circulation phenomenon was simulated and two circulation patterns were found which can be interconverted.•Preferred conditions for improving the oil recovery rate was discussed in detail.
Characterizing the trapped phase in porous media is essential for many engineering applications, such as enhanced oil recovery, nuclear storage, and geological sequestration of CO2. This study aims to study the distribution, evolution, and influencing factors of the remaining oil in the process of water flooding at the pore scale. The single-connected pore space model was established by reconstructing the real micron CT scanned images of carbonate rocks. The VOF (volume of fluid) method using FSF (filtered surface force) formulation was adopted on OpenFOAM platform to simulate the oil-water two-phase flow process at the pore scale. Different wettability and capillary number were considered in the model. The accuracy of the model was proved by comparing with previous experimental results. The results showed that in the process of water flooding, the complex pore structure would lead to the generation of remaining oil, and the phase circulation phenomenon can be observed in the remaining oil and presents two distribution forms: co-current driven flow and lid-cavity driven flow. It also revealed that the phase recirculation increases the viscous dissipation. Further research also showed that the two forms of recirculation could be transferred by changing the wettability and that a higher capillary number was more beneficial for reducing the remaining oil saturation.
•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.
•A flow boiling model in a vertical narrow rectangular channel is constructed.•The characteristics of the flow pattern rely on the height of the channel.•The dynamic characteristics of flow boiling ...are analyzed.•The fluctuation of heat transfer has no obvious regularity in the FDB regime.•Most of the regions are dominated by saturated nucleate boiling.
This article experimentally and numerically investigates the flow boiling in a vertical upward narrow rectangular channel under low heat flux. VOF model for interface tracking and the phase-change Lee model are coupled to build a numerical model of a channel with a scale of 1200 mm × 250 mm × 2.75 mm. The temperature, velocity and phase distribution in the channel are obtained at different heights The bubble movement is analyzed and the two-phase flow regimes are classified. Furthermore, the local characteristic of flow boiling heat transfer along the channel and the effect of the bubble regimes on the heat transfer are studied. The results indicate that saturated nucleate boiling is the dominant boiling form under low heat flux.
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.
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.
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.
