Simulação de grandes escalas de escoamentos turbulentos não isotérmicos utilizando o método de elementos finitos

Abstract

A numerical study on forced and natural transitional turbulent convective flows is performed in this work. Large Eddy Simulation (LES) and the Finite Element Method (FEM) with structured and non-structured meshes are employed to solve the system of equations which govern unsteady and steady two-dimensional incompressible flows with heat transfer. The mathematical modeling is based on the conservation equations of mass, momentum, and energy in terms of streamfunction, vorticity, and temperature. The Galerkin scheme with linear interpolation functions for three-node triangular elements is used to approximate the governing equations. Regarding the turbulence approach, Large Eddy Simulation with sub-grid velocity structure function is used. Experimental and numerical comparisons with results from literature are carried out. A good agreement is achieved, except on the local Nusselt number in the case of turbulent natural convection in square cavities. The following problems are studied: three cases of turbulent forced convection in ribbed channels, one case of turbulent forced convection in a channel with a depression on the bottom wall, and one case of turbulent natural convection in a square enclosure. The results showed to be significantly influenced by the boundary conditions and the mesh refinement. The flow analysis results are obtained considering high Reynolds numbers in forced convection and high Rayleigh numbers in natural convection. Not only are streamfunction, temperature and velocity distributions presented, but also the local, average, and global Nusselt numbers in function of thermal and geometrical parameters.