Jing Lou

A New Multidimensional Drift Flux Mixture Model for Gas–Liquid Droplet Two-Phase Flow

A new multidimensional drift flux mixture model was developed to simulate gas–liquid droplet two-phase flows. The new drift flux model was modified by considering the centrifugal force on the liquid-droplets. Therefore the traditional 1D drift flux model was upgraded to multidimension, 2D and 3D. The slip velocities between the continual phase (gas) and the dispersed phase (liquid droplets) were able to calculate through the multidimensional diffusion flux velocities based on the new modified drift flux model. Through the numerical simulations comparing with the experiments and the simulations of other models on the backward-facing step and the water mist spray two-phase flows, the new model was validated.

Simulations of Flow Transitions in a Vertical Pipe Using Coupled Level Set and VOF Method

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.

Numerical Simulation of Three-Fluid Stratified Flow Using the Level-Set Method

Laminar three-fluid stratified flow which involves two different moving interfaces is numerically investigated in a two-dimensional domain in this paper. These interfaces are captured using the level-set method via two level-set functions. The effects of various parameters including Froude number Fr and Weber number We as well as the initial locations of the two interfaces on the evolution of the two interfaces are investigated. It is found that the decrease of We number increases the entry length. For a given volumetric flow rate ratio, the interfacial location at fully developed flow is identical irrespective of the Froude and Weber numbers as well as the initial interfacial location at the inlet. The interfacial locations for fully developed flow show distinct behaviors under different flow rate ratios and viscosity ratios. Increase of volumetric flow rate and viscosity for any one of the fluids increases the pressure drop in the channel. The study of pressure gradient reduction factor (PGRF) shows that it is possible to achieve pressure gradient reduction by introducing less viscous fluids in the transportation of a more viscous fluid.

Numerical Simulation of Water Jet Flow Using Diffusion Flux Mixture Model

A multidimensional diffusion flux mixture model was developed to simulate water jet two-phase flows. Through the modification of the gravity using the gradients of the mixture velocity, the centrifugal force on the water droplets was able to be considered. The slip velocities between the continuous phase (gas) and the dispersed phase (water droplets) were able to be calculated through multidimensional diffusion flux velocities based on the modified multidimensional drift flux model. Through the numerical simulations, comparing with the experiments and the simulations of traditional algebraic slip mixture model on the water mist spray, the model was validated.

Simulation of Bubbly Flow in a Vertical Pipe Using Discrete Phase Model

Bubbly flow is widely encountered in many engineering applications, such as those in chemical and nuclear systems, bubble column reactors and oil transportation pipes. Therefore, understanding of bubbly flow in a bubble-liquid flow system is extremely important. In this paper, bubbly flow involved with thousands of bubbles in a vertical pipe is numerically simulated. The motions of the bubbles are tracked using a Discrete Phase Model (DPM) and bubble-bubble interactions are simulated through the model of discrete element method (DEM). The effects of bubble diameter and bubble inlet velocity on the bubble flow trajectories are studied. Comparisons are made between the flow field with and without considering bubble-bubble collision. In addition to these, the breakup of bubbles on the flow field is also investigated.