Tesis doctoral de Lluís Jofre Cruanyes
The present thesis aims at developing a basis for the numerical simulation of multiphase flows of immiscible fluids. This approach, although limited by the computational power of the present computers, is potentially very important, since most of the physical phenomena of these flows often happen on space and time scales where experimental techniques are impossible to be utilized in practice. In particular, this research is focused on developing numerical discretizations suitable for three-dimensional (3-d) unstructured meshes. in detail, the first chapter delimits the considered multiphase flows to the case in which the components are immiscible fluids. In particular, the focus is placed on those cases where two or more continuous streams of different fluids are separated by interfaces, and hence, correspondingly named separated flows. Additionally, once the type of flow is determined, the chapter introduces the physical characteristics and the models available to predict its behavior, as well as the mathematical formulation that sustains the numerical techniques developed within this thesis. the second chapter introduces and analyzes a new geometrical volume-of-fluid (vof) method for capturing interfaces on 3-d cartesian and unstructured meshes. The method reconstructs interfaces as first- and second-order piecewise planar approximations (plic), and advects volumes in a single unsplit lagrangian-eulerian (le) geometrical algorithm based on constructing flux polyhedrons by tracing back the lagrangian trajectories of the cell-vertex velocities. In this way, the situations of overlapping between flux polyhedrons are minimized. complementing the previous chapter, the third one proposes a parallelization strategy for the vof method. The main obstacle is that the computing costs are concentrated in the interface between fluids. Consequently, if the interface is not homogeneously distributed, standard domain decomposition (dd) strategies lead to imbalanced workload distributions. Hence, the new strategy is based on a load balancing process complementary to the underlying domain decomposition. Its parallel efficiency has been analyzed using up to 1024 cpu-cores, and the results obtained show a gain with respect to the standard dd strategy up to 12x, depending on the size of the interface and the initial distribution. the fourth chapter describes the discretization of the single-phase navier-stokes equations to later extend it to the case of multiphase immiscible flow. One of the most important characteristics of the discretization schemes, aside from accuracy, is their capacity to discretely conserve kinetic energy, specially when solving turbulent flow. Hence, this chapter analyzes the accuracy and conservation properties of two particular collocated and staggered mesh schemes. the extension of the numerical schemes suitable for the single-phase navier-stokes equations to the case of multiphase immiscible flow is developed in the fifth chapter. Particularly, while the numerical techniques for the simulation of turbulent flow have evolved to discretely preserve mass, momentum and, specially, kinetic energy, the mesh schemes for the discretization of multiphase immiscible flow have evolved to improve their stability and robustness. Therefore, this chapter presents and analyzes two particular collocated and staggered mesh discretizations, able to simulate multiphase immiscible flow, which favor the discrete conservation of mass, momentum and kinetic energy. finally, the sixth chapter numerically simulates the richtmyer-meshkov (rm) instability of two incompressible immiscible liquids. This chapter is a general assessment of the numerical methods developed along this thesis. In particular, the instability has been simulated by means of a vof method and a staggered mesh scheme. The corresponding numerical results have shown the capacity of the discrete system to obtain accurate results for the rm instability.
Datos académicos de la tesis doctoral «Numerical simulation of multiphase immiscible flow on unstructured meshes«
- Título de la tesis: Numerical simulation of multiphase immiscible flow on unstructured meshes
- Autor: Lluís Jofre Cruanyes
- Universidad: Politécnica de catalunya
- Fecha de lectura de la tesis: 25/07/2014
Dirección y tribunal
- Director de la tesis
- Assensi Oliva Llena
- Tribunal
- Presidente del tribunal: arthur e.p. Veldman
- andrey Gorobets (vocal)
- (vocal)
- (vocal)