Selecting the Right Physics Interface
The Porous Media and Subsurface Flow branch () included with the CFD Module has a number of subbranches to describe momentum transport. These can be added either singularly or in combination with other physics interfaces modeling mass and energy transfer, and even chemical reactions.
Different types of flow require different equations to describe them. If the flow type to model is known, then select it directly. However, when you are not certain of the flow type, or when it is difficult to obtain a solution, you can instead start with a simplified model and add complexity as you build the model. Then you can successively advance forward, comparing models and results. For porous media flow, the Darcy’s Law interface is a good place to start if this is the case.
In other cases, you might know exactly how a fluid behaves and which equations, models, or physics interfaces best describe it, but because the model is so complex it is difficult to reach convergence. Simplifying assumptions can be made to solve the problem, and other physics interfaces can be better at fine-tuning the solution process for the more complex problem. The next section gives you an overview of each of the physics interfaces to help you choose.
Table 7-1: The Porous Media Flow Default settings.
Physics Interface Label
Name
Compressibility
Neglect Inertial Term
Pore Size
Darcy’s Law
dl
Compressible flow
n/a
Low porosity and low permeability, slow flow
Two-Phase Darcy’s law
tpdl
n/a
n/a
Low porosity and low permeability, slow flow
Brinkman Equations
br
Incompressible flow
Yes - Stokes–Brinkman
High permeability and porosity, faster flow
Free and Porous Media Flow, Brinkman
fp
Incompressible flow
Not selected
High permeability and porosity, fast flow
Figure 7-1 is an example of the Settings window for Brinkman Equations where you can select either Compressible or Incompressible flow, and either normal or Stokes Brinkman flow. For Darcy’s Law interface, you can select Incompressible, Compressible, Compressible, linearized, or Ideal gas as a fluid type under Porous Medium/Fluid node.