[ms42]

Hi,

I'm trying to simulate flow over a formula sae car to find total downforce, drag, and center of pressure. I am able to run each simulation with reasonable convergence (fluctuates +/- ~3% on downforce and drag after settling). However, I noticed that there are no prism layers being generated on the wind tunnel box or around the car. Changing the number of layers or boundary layer thickness anywhere from 10% to 300% of the base size (.05 m) doesn't affect anything.

I did a very rough calculation and the boundary layer is probably around .75 to 1 inch thickness at the end of the longest, relatively straight part of the car, so I have the total thickness set to 1 inch now.

I don't know if it makes a difference, but I've been using K-omega (with SST) primarily for the solver, with the ground as a slip plane, top as wall, sides as symmetry planes, and front as inlet and back as outlet for the wind tunnel box. I have a couple boxes for volume control/mesh refinement around the car and the wake of the car and have used a surface control for all the wind tunnel surfaces. I'm using prism layer, trimmer, and surface remesher.

I have tried making a plane section, but I can't figure out how to get it to show the mesh. Even if I could get it working, changing prism layer settings and remeshing doesn't do anything; it keeps the mesh it's already made and doesn't change anything.

Any help would be greatly appreciated. If pictures or further information is needed, I can provide.

[fluid23]

There are a few reasons why you might not see prism layer being generated. First, regarding the wind tunnel walls I don't think you will see prisms generated on symmetry planes. These should only generate on wall boundaries (slip and no-slip).

The reason you are not seeing prisms on wall boundaries is a little less straight forward. This is almost certainly a conflict of oversight in your mesh settings. Lets start with the obvious. Usually when I have issues with the prism layer the first place I look are the volumetric controls. Disable all of these and remesh, do you still not see any prism layers?

Also, having a mesh scene would be helpful. I will walk you through getting plane cut showing your mesh, just follow along:
1) Mesh your model, if not already done.
2) Create new scene > mesh scene.
3) For the Mesh 1 Displayer this should default to contain all regions. If not, select them for input parts.
4) Under the properties window for Mesh 1, change opacity to 0.1 and then toggle off mesh and toggle on outline so only surfaces are shown. (this will give you a ghost view of your domain that will help you determine where your cut plane is located). Leave this scene open.
5) Next, go to derived parts > new > section > plane.
6) In the Edit window set the origin and normal so that your plane is located where you want it.
7) Verify that new geometry displayer is selected in the dispay box in the Edit window and click, 'create'. You should now see this plane appear inside your ghost domain.
8) Go back to the Mesh scene you created and select Section Geometry 1 displayer then toggle on Mesh.

You should now be able to see your mesh. Feel free to hide the ghost domain if it is in your way.

[ms42]

Originally Posted by MBdonCFD

There are a few reasons why you might not see prism layer being generated. First, regarding the wind tunnel walls I don't think you will see prisms generated on symmetry planes. These should only generate on wall boundaries (slip and no-slip).

The reason you are not seeing prisms on wall boundaries is a little less straight forward. This is almost certainly a conflict of oversight in your mesh settings. Lets start with the obvious. Usually when I have issues with the prism layer the first place I look are the volumetric controls. Disable all of these and remesh, do you still not see any prism layers?

Also, having a mesh scene would be helpful. I will walk you through getting plane cut showing your mesh, just follow along:
1) Mesh your model, if not already done.
2) Create new scene > mesh scene.
3) For the Mesh 1 Displayer this should default to contain all regions. If not, select them for input parts.
4) Under the properties window for Mesh 1, change opacity to 0.1 and then toggle off mesh and toggle on outline so only surfaces are shown. (this will give you a ghost view of your domain that will help you determine where your cut plane is located). Leave this scene open.
5) Next, go to derived parts > new > section > plane.
6) In the Edit window set the origin and normal so that your plane is located where you want it.
7) Verify that new geometry displayer is selected in the dispay box in the Edit window and click, 'create'. You should now see this plane appear inside your ghost domain.
8) Go back to the Mesh scene you created and select Section Geometry 1 displayer then toggle on Mesh.

You should now be able to see your mesh. Feel free to hide the ghost domain if it is in your way.

Thank you very much, I believe the prism layers were there the whole time. The automated mesh representation didn't show the prism layers, but the volume mesh representation on the plane section did. Whenever I changed prism layer settings, I only did surface mesh to test since it takes 10 minutes to make surface and volume mesh each time. Prism layers don't change until volume mesh is generated.

[ASLAN_1987]

Two adjacent wall boundaries may lead the failure of generating prism.