Study of liquid-gas multiphase flow by using a computational fluid dynamics method based on particles.

Abstract

The main goal of this work is to analyze numerically the gas-liquid multiphase flows that are present in many engineering fields. A computational fluid dynamics method will be improved to make it capable to study the interaction between different fluid phases. This simulator has been developed during the last ten years in the Numerical Offshore Tank Laboratory in the University of São Paulo. The author of this work plan participated intensively in the development process.The simulator is based on a method called Moving Particle Simulator (MPS). MPS is a numerical method to simulate incompressible flow using particles to represent the domain described in a Lagrangian way. This method has advantages when comparing to traditional mesh methods because it does not have numerical diffusion and it is easier to handle the interface between fluids. The Lagrangian aspect of this method simplifies the simulation of fluid flows with free surface, large displacements and deformations, fragmentations and fluid merging, multiphase flows and multiphysics phenomena.The MPS/TPN numerical simulator development started during the author's master course. It was used to analyze highly non-linear hydrodynamics with free surface problems. During the author's doctorate course, a team was formed to upgrade the simulator to analyze problems with viscosity, surface tension, rigid body and elastic body dynamics and heat transferring. It was applied to analyze high amplitude waves, sloshing, floating bodies with the dynamic of the sloshing inside tanks, sloshing suppressing systems, porous media flow, mixers, oil leakage, dam breaking, etc.Due to its flexibility, the simulator functionalities have been extended to solve problems in the civil construction field such as fresh concrete flow and multiphase flow in building sewage system.Talking specifically about the simulation of buildings sewage system, the correct modeling of gas and liquid phases and their interactions are essential to accurately predict the system dynamic. To simulate the multiphase behavior the challenge is addressed in the fluid interaction different densities. If the interacting fluids have specific mass with different magnitude order, unreal high velocity fields will show up on the fluid with low specific mass. It will affect negatively to the calculation accuracy.In this research, gas-liquid multiphase flow solutions present in the literature will be evaluated. Based on these analyses, the simulation software will be upgraded with the most suitable solutions and modifications will be proposed according to this project needs. This software will be tested and validated to make it applicable to model and to investigate real cases of buildings sewage systems. Other applications as oil transportation gush inside risers, oil and gas production flow will also be considered.Limitations of the number of particles will be eliminated applying parallel processing and multiresolution techniques. The software already is parallelized using shared memory and distributed memory systems but they can be improved.