Porous Media Characterization using ANSYS CFD

Hi, this is Mingyao from Ozen Engineering, and in this video, I'll be looking at how to characterize a porous media from a CFD simulation. Here I have a plate with lots of holes on it, so it's a grill. If we were to model these geometries in detail, it could be computationally expensive.

We need a huge mesh to capture all of the holes here. We've had customers with tens of thousands of holes and nozzles to model, so one way to model this more efficiently is to treat this as a porous media. I'll start by creating a unit sector, a unit section for a porous media.

I'll create a model that looks like this and extend it by 25 millimeters on each side of the plate. Then, we'll do an interference check and subtract the solid part. So that's it. We have a couple of small cylinders here.

I don't need the grill for my analysis, so I'll suppress it, and this will be the simulation geometry. Coming back to ANSYS, we'll set up a Fluent simulation. Here is the meshing tool, and we'll use a few easy-to-use mesh controls.

We want five layers through the thickness to better capture near-wall flow of this structure. Since we're using ANSYS Fluent, we need to define the mesh boundary names. I'm using the letter N on the keyboard to call this the inlet.

We'll name this the outlet, and the other four surfaces are all symmetry surfaces. We have a small model, so we could use a few cores on my computer to run it. The fluid is going to be air. We have different boundary conditions already defined, such as inlet, outlet, and symmetry.

We'll compute the inlet pressure, which is just one Pascal. We can take a look at the results quickly here. I'm going to create a contour plot on that plane of the pressure. That shows you the pressure. We can also look at things like velocity, so how the flow is going.

Now, we should be able to run a series of simulations. Let's do 1 and 10. Update all the design points. And it should run my simulations at different inlet velocities. The first set of simulations completed.

I'll fill it in by maybe a couple of extra ones in the initial part to see what the results look like. Simulation has completed, and we have a set of data here. So let's copy this data into Microsoft Excel. We'll just do this and copy it over here.

We want to calculate the viscous and inertial resistance. So what we do is turn this into a quadratic equation and then find the coefficients and then calculate C1 and C 2. The inertial resistance is C2, which is the first part, the squared value here.

So this is the inertial resistance, or C1 here, that's equal to this value divided by the viscosity and divided by the thickness. We need the density, viscosity, and thickness. So the density is 1.225, and viscosity is this value. And the thickness is 5 millimeters.

When we turn something into a coarse media, we need the viscous resistance and inertial resistance. The only thing we want to do is add another porous media to the cell zone for the porous area. So this will be a porous media. And let's put in our viscous resistance.

The flow is going to be in the y direction, and our viscous resistance is this value 2.21e to the 8. And we'll put in our inertial resistance values. Finally, we want to put in our fluid porosity. So the porosity is the porosity. We'll put that in there too. And that's it.

So we can go ahead and run the simulation because everything is linked together as parameters. We have another set of inlet velocity, and we will automatically calculate the new Delta P. We'll get rid of the 10 here so that we're not trying to span quite so many orders of magnitude.

But this gives you hopefully some idea of if we want to match the flow rates in from 0.1 meter, so 10 centimeters per second, to 10 meters per second, we're doing a pretty good job of matching the pressure drop to flow rates.

And you can now run a simulation that's many orders of magnitude faster by using this type of porous media approach. Using ANSYS Fluent, there are many other options and parameters available for porous media.

You can do additional corrections to try to span greater ranges and make sure that the results are accurate. But this basic type of calibration can be done very quickly using SSE-FD. I hope this helps. If you have any questions, feel free to reach out to us at ozen-engineering.com.

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