Modelagem matemática e computacional de escoamentos turbulentos bifásicos em regime denso

Abstract

Turbulent flows in multiphase systems represent a significant challenge in classical physics, offering an open field for research. Understanding this phenomenon can lead to important advancements with engineering applications. The objective of this thesis is to develop a model to assess how the presence of a dense particle regime in a fluid affects turbulence. It is known that particles immersed in a fluid alter its viscosity. Utilizing the Euler-Lagrange formulation and the Large Eddy Simulation (LES) methodology, we apply a low-pass filtering to the equations of mass balance, linear momentum, and energy. We propose a triple decomposition of the Eulerian velocity field to account for fluctuations caused by the relative motion between the continuous and dispersed phases. We conduct simulations of two distinct problems. The first problem is an iconic case of bubble injection at the bottom of a water-filled vertical column. The second problem involves simulating a full cone spray case. We also propose a modified viscosity and drag force based on the volumetric fraction of the continuous phase. We evaluate different closure models for turbulence and compare the results of the three-way formulation with the two-way formulation. The results of the computational experiments are compared with those of a physical experiment. The turbulent kinetic energy obtained in the physical experiment closely matched the Smagorinsky model with a constant Cs = 0.15. The analysis of the collected data validates the proposed model and demonstrates how the modeling of dense turbulent flows incorporates more physics for describing the phenomenon.