In this week´s blog post we will look more in detail at the new phasic porous media compatibility with EMP. This new feature was shortly introduced here: [Simcenter STAR-CCM+ Multiphase News Version 2506 – Volupe.com]. But the TLDR is that porous media was not compatible with EMP before. Using EMP there is generally a strict interaction between the phases, usually a liquid and gaseous phase. While in a porous media the liquid interaction with the gas is secondary to the liquid interaction with the solid component of the porous media.
Resistances
If we look at the equation for the body force vector that is part of the momentum equation for the physical velocity formulation, we see the usual resistance tensors.
When using the Eulerian multiphase (EMP) model the porous viscous resistance Pv is computed based on the intrinsic permeability of the porous medium and the relative permeability of each fluid phase. It reduces the need to specify loss data using curve fitting to determine the resistance coefficients. The phase permeability is given by:
Let’s try to go over the different components of these equations. The intrinsic permeability of the porous medium is a constant value, it is a physical property of a porous material, like rock or soil and represents the ability to transmit fluids, independently of the fluid properties like density or viscosity. It is measured in cm2 or m2 or Darcy (Typical range for sand in 1e-7 cm2 to 1e-5 cm2, where one Darcy is equivalent to approximately 9.869e-13 m2).
The relative permeability of the phases is a function of constant phase properties, like maximum relative permeability of a phase, typically for water a value close to 1, and the effective saturation of a phase. The effective saturation of a phase is calculated using the irreducible saturation of the phase in the porous medium. The irreducible saturation is defined as the lowest saturation of the media achieved in a porous media when another fluid, like oil or gas, is forced to displace it. An example is when having a porous rock filled with water and then force air through it to “clean” the water out. The irreducible saturation is then represented by the water left in the rock after this process. The volume fraction of the phase also comes into play in calculating the effective saturation of a phase.
Example
Let’s assume we have a porous media barrier that partially block a liquid flow. At the inlet we have a distinct water level that moves towards the porous domain. The values used in the example are:
A video from such a simulation is presented below. Here, the barrier (the half sphere) shows the relative permeability of water in the porous medium. If we do a snapshot calculation (use the values we see in the animation near the end) of this for volume fraction one of water, we get the same Relative permeability of water at 0.8. The rest of the domain shows the water velocity where the volume fraction of water is above 0.5. The liquid surface is also included.
We see that the water is both transported above the obstruction and through it since we have a porous media. This is an interesting application now available in Simcenter STAR-CCM+.
I hope this has given you some ideas of how you can use Simcenter STAR-CCM+ with this new functionality. As usual, reach out to support@volupe.com if you have any questions.
Author
Robin Victor
support@volupe.com