Read Time: 20 min

Intended Audience: new-to-Luminary, interested in Porous Media modeling

Simulation Time: ~2 min

Simulation Cost: 2 credits

In this Tutorial we focus on internal flow through an exhaust system, where a particular part of the system is modeled using a Porous Media Model (PMM). You will learn:

and you can use the tutorial to investigate the difference in the solution when the PMM physics modeling is activated vs. not.

A catalytic converter is a vehicle emissions device that converts engine exhaust pollutants into nitrogen, carbon dioxide, and water vapor. Exhaust gasses enter through the inlet, then pass through a complex, honeycomb-shaped substrate made of Platinum, Rhodium, and Palladium to initiate a chemical reaction.

In CFD, the substrate is modeled as porous media due to its complex structure. Geometrically resolving the internal details of the media would require an excessively fine (small length scale, high cell count) mesh that would make such a simulation impractical from a cost perspective. The porous media model framework allows the simulation to impose the required flow restrictions, applied in a bulk fashion on the fluid, in a computationally efficient manner.

This catalytic converter domain is made up of three separate volumes: the inlet, the substrate, and the outlet. As exhaust flows through the inlet, the pressure will drop as it passes through the substrate. You'll apply visualization filters to determine the flow pattern and view the pressure drop.

Navigate to the Project tab and click create New Project. From the modal, select the sample project titled "Catalytic Converter: Porous Media Modeling".

This will create a new project where the mesh described below has been loaded, but no other inputs have been specified. When you enter the project you will be placed in the setup environment with a computational mesh loaded:

The most important aspect when starting a new simulation is to familiarize yourself with the geometry model, especially when you are not the person who created it. In the Geometry Tree of the left you'll see the three volumes that have been generated:

Additionally there are surface groups for each of these volumes that will be used to define boundary conditions, several of which are used to communicate between the volumes (interfaces):

If you don't want to manually setup all of these inputs as you follow along, you can upload this settings file into the Project to automatically fill in the setup configuration for you. The steps to do this are:

You'll be taken to the simulation tab for this run. Once it's finished running, you'll apply visualization filters to view the results.

Create a slice to view the pressure distribution throughout the catalytic converter:

It's hard to see the flow through the device, so hide the model's surfaces to get a better view. In the Geometry panel, click the eye icon to the right of Surfaces to hide all surfaces.

You'll notice pressure increase as air hits the substrate, then drop as it flows through the rest of the device.

Finally, apply a surface LIC filter to get a better view of velocity distribution through the catalytic converter:

You'll notice high velocity through the inlet, then the air slows and starts to recirculate as it hits the porous volume. Velocity drops significantly through the substrate before speeding up again at the outlet.