Abstract

Vertical plunging jet is a typical multiscale two phase flow problem, in which a large amount of microbubbles are formed by the impingement of liquid jet with free surface. Traditional numerical simulation methods are difficult to reproduce both the large scale phase interface evolution and the small scale microbubbles at the same time. In this paper, a hybrid VOF/Euler-Lagrange method is adopted to simulate the vertical plunging jet flow problem. The large scale air-water interface is captured by VOF method and the microbubbles are modeled as Lagrange points. Special algorithms are designed to realize a smooth transformation between two frameworks. Results indicate that satisfactory simulation effect can be achieved with high efficiency by using the new method.

INTRODUCTION

Although computational fluid dynamics (CFD) algorithms have made great progress in recent years, the prediction of multiphase flow problems remains a unique challenge for numerical simulation. One of the most important reasons is that many multiphase flow problems involve a broad range of scales. This is also common in ocean-related problems, such as wave breaking. The evolution of waves is a typical large scale flow phenomenon, while the bubbles and droplets appear near the free surface are typical small-scale flow phenomena. Traditionally, there are limitations in the simulation methods for twophase flow phenomena at different scales. For example, free surface flows were usually simulated by some mature interface capture methods such as Volume of Fluids, Level-set and Front-Tracking method. These methods rely on computational grids to describe the phase interface, which needs extreme high computational cost to capture large numbers of bubbles and droplets at small scales. On the other hand, there are two well-known simulation methods designed for discrete multiphase flow problems, Euler-Euler method and Euler- Lagrange method. In both methods, the discrete phase such as bubbles and droplets are modeled according to specific assumptions. The computational cost is obviously reduced, but it cannot simulate phase interface evolution. Therefore, there is a strong need to develop a hybrid method to solve the multiscale two phase problems.

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