Multiple Physics Models in Different Domains - ANSYS CFX

Hello, my name is Jesus Ramirez and I am part of the technical staff of OSINT Engineering. Today I am going to show you how to use different physics models in different domains inside ANSYS CFX. This is a very common question from our customers.

Then in this video, I am going to explain how to do this easily. Let's look. First, I am going to create a simple geometry using ANSYS SpaceClaim. I am going to pull this for 75 mm. Now I am going to create another 25 mm and I am going to pull it 75 mm. Then we have only one solid.

I am going to split this to have two different solids. Then I am going to split this body using the spline and now we have two different solids. I am going to call this "large" and I am going to call this "small." Great. And just for best practices, this will be my inlet. And this is my inlet.

And this will be my outlet. Once we have this, we move into the mesh part to do the mesh and then after that, the CFX frame. Let's look at the mesh process. I am going to create the mesh. Then I am just going to create a default mesh. Then just run the thing.

And then, as a best practice, include some inflation layers. Now, let's change this to CFD. CFX. And generate the mesh. Once the process finishes, we have a mesh. I am not going to start playing with this. This is a demonstration. Then we close this and move to the CFX setup.

Before starting with the CFX setup, I want to say that something I didn't show previously was the shared topology process. If you want to share topology, that's a good option. That's a good practice sharing topology between objects. You can do it directly using ANSYS SpaceClaim.

And if you want to know more about how to do it, you can see in our channel. One of the videos is focused on the shared topology process. Okay, let's continue. Here we have the geometry and the mesh. Then what I'm going to do is, if you see, we have only one domain. I'm going to create another one.

I am going to click "Analysis," then "Insert Domain." This will be the small one. I am going to click "OK." And insert domain. In the locations, I am going to select this one, the small one. And click "Apply." Now, we have two different domains here and here, the large and the small.

Then, for example, if I go here, I will change this to shared stress transport. And I am going to click "Apply." Now, if I go to the small domain, I will see that the turbulence also changed to shared stress transport.

If I go back to K-epsilon, this one, let's say I want to use the K-epsilon in the small one. If I go back to the large, I will see that the turbulence also changed to shared stress transport. If I go to the large, then I will see that the K-epsilon is also in the large one.

It means that we have constant physics between the solids. If I change the physics of the fluid models in this domain, the fluid domains will change for this one. And of course, if I change the fluid models for this domain, then the model will change for the small one.

If you want to avoid that, then what you need to do is go here to files, and then edit options here in general. We have beta options, beta features, and you can put like, you have here constant domain physics. Then uncheck this box.

When you uncheck this, then you can define different fluid models or different physics models for different analyses.

For example, I am here in the large model, then I am going to keep this like K-epsilon, and I am going to go to the small model, and I am going to change it to shear stress transport.

And now you will see the small has the shear stress transport, and if I go back to the large, now we have the K-epsilon scalable model that is different. Now, I can use different models. So, you can see that I have different fluid models for each domain.

Now, let's say some questions that we received are: if I want to model turbulence here, and this part may be as a laminar flow or vice versa, this as a laminar region, and this as a turbulent region. Then, one option in CFX is to change the turbulence model to shear stress transport.

And here in advanced turbulence, you can see that the shear stress transport is not the same as the laminar flow. So, what we are going to do is change the turbulence control, change the eddy viscosity to zero.

Then, if we put this value here, zero, with the shear stress transport, we are somehow modeling the flow as an approach to laminar.

And the other one, if we go back, we have the shear stress transport, that was the model we defined previously, but if you see in the advanced control, we don't have the eddy viscosity enabled. That's good. Now, what we need to check is, for example, we have here air.

I'm going to change this to water. Click "Apply." Also, I'm going to change this to water because I need to have the same grid. And I can run this and post-process my results. I hope you enjoyed this video. And if you have any questions, please contact us through our website.

Thank you very much for your attention. Bye-bye.