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[galkhamis]

Hello,

 

I am trying to model a very simplified version of a greenhouse and I am having trouble extracting volumes for the entrapped air inside the greenhouse since the regions don't have inlets or outlets. There are two covering layers in the model and two entrapped areas of interest. The first is the gap between the outer layer and the inner layer (Area 1 in the figure). The second area is the inside of the inner layer (Area 2 in the figure). Can anyone show me how to extract those areas into volumes so I can assign then into fluid regions in my model (I am using the thermal model template)? I uploaded the geometry for reference as well. 

 

 

 

[peteroznewman]

You want a surface to divide the large body into two regions. The problem is you have a solid, not a surface.

1. Hide the full volume solid.

2. Select the three outer faces on the dividing solid. Ctrl-C and Ctrl-V to copy and paste those faces. Now you have a surface body. Delete the Solid.

3. Double click on one edge of this surface and click the Pull Tool. Pull the edge out.

4. Turn on the full solid, click the Combine Tool. Select the solid and cut it with the surface.

5. Click the Select tool, select the Surface and hit the Delete key. Now you have the two solids that share three coincident faces.

6. Click on the Workbench tab and click the Share Tab to use Shared Topology so the mesh will be connected at these faces.

[galkhamis]

Hi,

 

Thank you for your reply,

I downloaded the file you attached and I see that you no longer have a top surface for the inner layer (as in the attached picture below). the whole point of the inner layer is that top surface (plus the two sides), which will be assigned materials later in the simulations. 

 

 

to iterate, I am trying to model a greenhouse that contains two covering layers (outer and inner), each has a thickness and will be assigned a material. The outer layer will be assigned heat flux (from the sun) and the point is to observe the temperature of the air inside the inner layer. We are observing this temperature to gauge the effectiveness of different materials assigned to the two covering layers. Since the two layers are separated by a significant distance (labeled Area 1 in the figure included in the original post), I need that as a region that I can assign materials to (which is air in this case) later in the simulation. I also need Area2 as a volume so I can assign air to that as well and see how the temperature of this air rises or falls depending on the materials used for the two covers, given a constant heat flux. 

[peteroznewman]

Sorry, I assumed the outer body was a solid volume when it was actually a hollow, very thin-walled shell, with a fully closed exterior. Knowing that, the extra step is to convert the shell back to a filled solid. One simple way to do that is to copy and paste the end face, then pull that face to the other end to make a filled solid. Then the splitting shown above will work.

There was a clue above that something was wrong because after sharing, I expected to see 3 faces and it showed 4 faces.  

This is still not what you were expecting, just two volumes for the air. What about the wall? There is an efficient way to build a model in Fluent. The wall Boundary Condition between the two volumes of air will be defined in Fluent as a wall that can be given thermal properties like material and wall thickness. In meshing, I defined a named selection called wall-inner.

In Fluent, after the Energy equation is turned on, I can edit the properties of the Wall Boundary Conditions and on the Thermal tab, enter the Wall Thickness and Material assignment for the wall.  The default solid material is Aluminum, but you just create the material you need and enter the conductivity.

I'm not the CFD expert, so someone who is might offer further guidance.

[galkhamis]

Dear peteroznewman

 

Thank you so much for your help so far. I think the two volume file is very close to what I am looking for. I am now trying to build on your geometry and trying to introduce the outer layer that would cover all the outer surfaces. I attempted following your first instructions by copping and pasting the outer faces (which creates a surface) then pulling that surface into a solid. However, I keep facing a problem while meshing (it keeps failing because of the boundary layer). I believe I am missing something while creating the outer layer geometry (or maybe while defining the boundary layer in the mesh) because the meshing works fine with only the two volumes you built. I am not sure how to fix that, can you help me build the outer layer for now? 

Once I get that right and get the meshing to work I will look into the inner layer that separate the two air volumes.

Thank you again,

[peteroznewman]

The two volume model has an outer wall, there is a named selection for it. I expected you would do the same on the outer wall as you did on the inner wall, except you would assign a heat flux to the outer wall to represent the solar heat input. That is what you said you wanted at the beginning.

It is possible to add an outer volume to represent the outside air. That outside air could convect heat away from the outer wall, but now you have to have an inlet and an outlet to the outside air domain. That just makes your model much bigger. Are you sure you want that?

[galkhamis]

Unfortunately, I am unable to open your Fluent file because I don't have the exact models. I am using DISCOVERY AIM 2020 R1.

Would you mind explaining how you make the wall Boundary Condition and I can hopefully do it in Discovery aim? 

I also think it is important that I add the convective effect of the outside air. I thought that I can apply that directly to the solid outer layer but if that does not work with the wall BC option, then I can use the enclosure tool to do that since I have the wind speed and the temperature of the surrounding air. The enclosure will also include the insulated ground.

[peteroznewman]

Ah, DISCOVERY AIM... it hides much of the gory detail that Fluent exposes. Maybe you should try Fluent itself.

Are you on the Student license or a Research or Commercial license?

If you are on the Student license, you can download and install ANSYS Student 2020 R1.  It can coexist with DISCOVERY AIM.

You don't need a body to be ground, you just identify the face that touches the ground as a wall. By default, all walls are insulated. I created a Named selection called Ground for you in my model.

[galkhamis]

I am using a license provided to me through my university (not a Student license) and don't have access to any other license. Is there anyway you can show me how to work the wall BC in your version and I will try my best to translate that into Discovery. I have a deadline to meet and would really really really appreciate the help to get this model running. 

Thanks again, 

[peteroznewman]

I am downloading AIM 2020 R1 so I can see what to do in that system.

[galkhamis]

I ended up downloading the ANSYS Student 2020 R1 version since AIM just kept giving me bad results even after enlarging the layers thicknesses. 

 

I opened your Workbench file and assigned the thicknesses and thermal properties to the walls as you adviced and got semi-reasonable results. However, I think it is essential that I include the convective effects to the outer layer of Area-1. Do you know of an easy way to do so besides creating a third volume (enclosure)? I attempted the enclosure method but kept running into issues while meshing and I am not sure how to fix any of them since this is my first time dealing with Fluent. 

 

I would really appreciate you help. Thanks!

 

[Miss Sadeghi]

I want to fill a tank with 90% paraffin and 10% air. How is this done in Ansys?

[Nanda]

Hello Miss,

Kindly post a new query with appropriate description and tags, this will reach to larger forum audience and resolved ASAP. You can paste a link of this forum discussion, if you feel this is related to your query.

This is recommended for two reasons:

1. You will get notified if you're owner of the post, when someone replies to you post.
2. Generally unanswered posts grab more attention than which already have prior comments.

Regards,

Nanda.

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