Simulation Of The Interface Movement And Pollutant Transport Of Multiphase Flow By VOF Method

Multiphase flow commonly exists in ecological system. The simulation of multiphase flow and pollutant transport are paid attention in recent years. In this dissertation, a numerical wave tank based on the theory of two-phase flow is built to study wave-current field and pollutant transport under the effects of water wave. Furthermore, the performance of tracking the interface of multi-phase by VOF method is testified.The wave is introduced by an oscillating plane wave-maker and an artificial damping layer is presented to absorb the reflection wave. The air-water interface interface is tracked by VOF method. The control-volume-based technique is used to convert the governing equations to algebraic equations that can be solved numerically. By comparing the theorical results, the correctness and the stability of our numerical wave tank is proved. The wave-current field is estabilished by introducing a uniform current into wave field. When the flow and wave spread in the same direction, the wavelength and amplitude become longer and shorter with respect to those of pure wave, respectively. When the flow and wave spread in the different direction, both wavelength and amplitude become shorter than those of pure wave. The results agree with the experiments of Kemp (1982).The pollutant transfer in the wave field is studied. Numerical results show that the pollutant transfer is controlled by the combined action of water particles motion and diffusion. The shape of pollutant transported area is ellipse and the concentration of pollutant satisfies of the normal Gauss distribution.It is found that the movement of the several interfaces is well determined by VOF method even in the case of strong nonlinearity and large distortion. Taking as an example, the gravity current surge such as the collapse of liquid column is simulated. The cases of different ratio of density and viscosity are studied and the liquid-liquid interfacial Kelvin-Helmholtz instability is observed. Numerical results show when increasing the ratio of density of liquid phases, the movement of liquid-liquid interface is becoming rapidly. Meanwhile, the horizontal gas-liquid free surface is not keeping horizontally and becoming swing. When the ratio of liquid viscosity is less than 5, it has no influence on the movement of liquid-liquid interface. The collapse of liquid column agrees with the results of MAC method of former approach. This shows the VOF method can be also applied in fast changeable interface tracking.