Narrow Results

This study implements a new solver (reactiveInterFoam) to simulate the component mass transfer alongside deformable gas–liquid interfaces. Mass transfer from the rising bubble in a quiescent Newtonian fluid is simulated. An effect of bubble hydrodynamics on the simultaneous diffusion reaction and selectivity of the cyclohexane oxidation process is investigated on a two-dimensional axisymmetric domain. The color function volume of fluid (CF-VoF) technique is applied to capture the deformable interface, and the continuous species transfer method is used to monitor the gas–liquid mass transfer behavior. Several simulations have been conducted to validate the model reliability to forecast component mass transfer from the bubble to the liquid phase, bubble shape, and flow field. Simulation findings approved that the rate of mass transfer is a function of boundary’s concentration, layer thickness, and bubble surface area. Furthermore, the selectivity increases by decreasing bubble diameter in both spherical and ellipsoidal regimes. The small bubbles with a lower Reynolds number have higher average selectivity. Comparing the simulated bubble shape and the grace chart indicates that the suggested numerical method can perfectly predict bubble regimes. The absolute average relative deviation (AARD%) of 14.59% has been observed between the terminal velocities predicted by the numerical simulation and six experimental measurements.

Based on volume of fluid (VOF) technique, the flapping motion of submerged turbulent plane jet in shallow water impinging vertically onto the free water surface was simulated. To study further on the flapping motion, the power spectrum density, the centerline velocity decay, as well as the mean velocity profiles of the jet were all investigated in this paper. The results are in great agreement with those of theoretical analyses, and the results show that the flapping motion is a new flow pattern of submerged turbulent plane jets.

Polymer-based micro/nano fluidic devices are becoming increasingly important to biological applications and fluidic control. In this paper, we propose a self-enclosure method for the fabrication of large-area nanochannels without external force by using a capillary-pressure balance mechanism. The melt polymer coated on the nanogrooves fills into the trenches inevitably and the air in the trenches is not excluded but compressed, which leads to an equilibrium state between pressure of the trapped air and capillary force of melt polymer eventually, resulting in the channels’ formation. A pressure balance model was proposed to elucidate the unique self-sealing phenomenon and the criteria for the design and construction of sealed channels was discussed. According to the bonding mechanism investigated using the volume of fluid (VOF) simulation and experiments, we can control the dimension of sealed channels by varying the baking condition. This fabrication technique has great potential for low-cost and mass production of polymeric-based micro/nano fluidic devices.

Spar Drilling Production Storage and Offloading (SDPSO) is a new type of deep ocean platform developed in recent years. The process of oil-water displacement is used for oil storage and offloading and the research on the accompanying heat flow has been significant. The wax precipitation and solidification at low temperature will particularly affect the flowing of oil in the displacement process. When the heat flow is concerned, numerical simulation requires large computation. It is necessary to develop an efficient numerical method for this calculation. As a kind of interface tracking method, the volume of fluid (VOF) method needs less computing resources compared with other multiphase numerical methods. As for thermal expressions, there are mainly two kinds of governing equations, i.e. temperature equation and enthalpy equation, and two kinds of interpolation scheme of heat conductivity, i.e. algebraic interpolation scheme and harmonic interpolation scheme. There is a need to find out which combination of governing equation and interpolation scheme of heat conductivity would result in a better precision for the heat flow. Therefore, four non-isothermal solvers, corresponding to the four combinations, are established. After comparison with an analytical solution, it is found that the temperature equation together with the harmonic interpolation scheme of heat conductivity results in better precision.

The level set (LS) and volume-of-fluid (VOF) methods are usually employed to simulate the two-phase flow. However every single method of them will face the mass conservative or accurate issues during the simulation. The coupled level set and volume-of-fluid (CLSVOF) method was not only able to conquer the shortages of the LS and VOF methods but also simultaneously keep the merits of both of the methods. In CLSVOF method the geometry reconstruction technology was employed to realize the coupling between LS and VOF. After the validation of single bubble rising cases, the CLSVOF method was used to simulate the complex transitional two-phase flows in a vertical pipe and the simulation results were compared to experiments.

Wave impact on one and two structural beams with rectangular cross section is simulated with a two-dimensional finite volume method, solving the unsteady Euler equations and employing a VOF-type method for the description of the free surface. Four different test series are carried out, each corresponding to a wave impact scenario in the experimental database of Sterndorff [2002]. For the case of wave impact on a single structural element the numerical results show good agreement with measured force time histories. In the computations featuring two beams, the prediction of the shadowing effect of the first beam on the second is in reasonable agreement with the experimental data. However, the force peak on the second beam is somewhat over-predicted. The calculations successfully predict a second peak in the force time series of the second beam, which is caused by airborne water shipped over the first beam. Throughout the work, spurious spikes of very short duration appear in the computed load time series, originating from the changing of the flow separation location along the lower edge of the beams.

A combined model was built of three main modules based on the Volume of Fluid (VOF) method, Discrete Element Method (DEM), and Finite Element Method (FEM). It was proposed to utilize this model to simulate the deformation of the rubble mound and the sandy bed due to surface wave action. The model included the full interaction between wave motion with free surface and replaceable separate particles of the rubble mound. Momentary arrangement of the fluid, particles and resulting permeability was tracked within a domain of time and two-dimensional space by maintaining cyclic data transfer between the three method modules. A new technique of porosity adjustment was presented. The model results were compared to small-scale laboratory test results. Based on the comparison, the VOF-DEM-FEM model appeared to be a promising tool to handle the destruction process of the rubble coastal structures built on a permeable bottom.

In this paper, to investigate a compound casting process for creating Al coating layer for Mg alloy, a computational fluid dynamics (CFD) model is developed using the VOF method to simulate the molten Mg drop impact on the Al substrate at solid state. A spreading factor, which is the ratio to the varied diameter of the Mg droplet after impacting on the Al substrate and its initial diameter before the impact, is used to describe and measure the impact process generated by the Mg drop, which could be divided into several steps: spreading, retracting and oscillating, and equilibrium as final step. Some key parameters are investigated via parametric studies: impact velocities, initial diameters of drop, the temperature of the Al substrate, which have important influences on the quality of compound casting products. The spread diameter of the Mg drop increases when the impact velocity and initial diameter of drop increase. While the impact velocities and initial diameters of the drop are larger than critical values, the liquefied Mg may partially have bubbles. The higher the temperature of the Al substrate is, the larger the spread diameters could be obtained, though oscillating and equilibrium steps take more time to finish in the CFD simulations developed.