Eventos Anais de eventos
COBEM 2021
26th International Congress of Mechanical Engineering
Finite element simulation for two-phase flow with a decoupled fluid interface
Submission Author:
Daniel Barbedo Vasconcelos Santos , RJ
Co-Authors:
Daniel Barbedo Vasconcelos Santos, Gustavo Rabello dos Anjos
Presenter: Daniel Barbedo Vasconcelos Santos
doi://10.26678/ABCM.COBEM2021.COB2021-1503
Abstract
In this research, finite element numerical simulation is used to describe bubble dynamics in two-phase flows. The accurate simulation of interface dynamics in two-phase flows is of crucial relevance for numerical analysis of two-phase heat transfer, which has widespread application in areas such as cooling of electric components, extraction and refinement of oil and gas, cooling of nuclear reactor equipment and more. The simulation is achieved by solving the incompressible Navier-stokes and energy conservation equations for two-phase flows, discretized through the Finite Element Method (FEM), where the interface and the fluid meshes are not explicitly connected. In order to respect the LBB condition, the mini element is used in the simulation, thus avoiding any artificial stabilization terms in the fluid motion equations. The non-linear convective term on the Navier-Stokes equation is solved by a first order semi-Lagrangian scheme, which allows large time steps. Two meshes are used, a fixed one for the fluid flow, and a moving mesh which describes the interface motion between fluids. The meshes are completely decoupled, the only link between them being the interface’s mesh position update, which is based on the velocity fields obtained from the fluid flow finite element solution. Despite the zero-thickness geometrical interface, which is defined by nodes and line segments, fluid properties are smoothed out to avoid numerical instabilities in the transition from one fluid to another. Surface tension is implemented according to the well-known continuum surface tension model, using the Laplace-Beltrami operator for curvature computation. The surface tension force is added explicitly to the Navier-Stokes equations as a volume force through the gradient of a Heavyside function that defines the interface's location, therefore the momentum equation is solved using a one-fluid approach. To prove that such an interesting numerical scheme is stable and accurate, we present three test cases, namely the static droplet, where parasitic currents are evaluated when surface tension is balanced by pressure, the oscillating droplet, where convection, surface tension and pressure are evaluated simultaneously, and gravity driven bubble, where the bubble rises inside a quiescent fluid dominated by gravity force. All presented results were run for several Reynolds numbers.
Keywords
bubble, Two-phase Flow, two-phase, finite element, FEM, Navier-Strokes, Continuum Surface, Laplace-Beltrami
