The level set function varies smoothly and defines the interface between the fluids. Such equations are, however, quite numerically challenging to solve due to the combination of the significant advective term, abrupt transition in the field, and strong coupling to the Navier–Stokes equations. The governing equations for the level set and phase field methods are a type of convection–diffusion equation, with the advective velocity coming from the Navier–Stokes equations. The transition (where the fields vary from 0 to 1 for the level set implementation and -1 to +1 for phase field) is quite abrupt in space, thus giving a good resolution of the two phases. These scalar fields vary smoothly between -1 and +1 everywhere and are used to define the fluid viscosity and density in the governing Navier–Stokes equations. Both of these methods introduce an additional scalar field (the level set or phase field function) to the modeling domain. To model this in COMSOL Multiphysics ®, we can use either the level set or phase field method. The surface tension effects can become important, as well as the effect of contact angles at wetted walls. However, if we want to model two immiscible fluids, then the fluid properties will vary significantly across the interface between the two fluids. The fluid properties (viscosity and density) are either constant or vary relatively smoothly in space as a function of temperature, pressure, shear rate, etc. Backgroundįluid flow is governed by the Navier–Stokes equations, which solve for fluid velocity and pressure fields everywhere within the modeling domain. The Two-Phase Flow, Level Set and Two-Phase Flow, Phase Field branches of physics interfaces in the Select Physics window. Here, you will find guidance for solving these types of fluid flow problems. When modeling fluid flow in COMSOL Multiphysics ® using any of the physics interfaces that fall under the Two-Phase Flow, Level Set or Two-Phase Flow, Phase Field application areas, there are several guidelines you can follow to ensure that your model converges and does so both in a reasonable time and to a reasonable result.
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