Learning Forum

[vedama]

I'm attempting to adapt a relatively simple geometry using the Geometry adaption. I imported a very fine mesh as a background mesh and attempted to adapt a very coarse mesh based on a combination of field variables and gradients. However. the adaption algorithm leads to the formation of left-handed faces and negative volume cells as you can see in the image:

[Rob]

You're trying to adapt an overset zone? It's clear why/how you've got a fine mesh but are trying to adapt a coarse mesh.

[vedama]

Hi Rob No, this is not an overset zone. It's a very simple 2D geometry. I used a fine mesh as the surface background mesh as seen below:

To my understanding, the coarse mesh will use the background mesh as a stencil to adapt toward. However, when I run the adapt function based on some field variables, it creates negative volumes.

[vedama]

To visualize what I'm referring to, see the image below where cells in the red circle are missing (non-positive volume) but hanging node adaption seems to work well in other areas (blue circle). I am looking for some guidance about why this is happening, please.

[Rob]

I suspect the cell aspect ratio is partly to blame, and when you adapt it the solver is twisting the result. What, and why are you trying to adapt for?

[vedama]

It's flow over an axisymmetric airfoil. I have a very fine, grid-independent result that has a lot of cells. I'm trying to arrive at the same result with fewer cells. I start with a coarse grid and adapt the solution using pressure, density and velocity gradients, and also allowing the geometry to adapt based on the grid-independent solution so the curvature of the airfoil is accurately captured.

[Rob]

I suspect you're pushing the tolerances and the solver is struggling to place the cell centre in the cell as opposed to in an adjacent cell. Are you using double precision?

[vedama]

I am using double precision, yes. Is there a way to fix the tolerance issue and test?

[Rob]

No, I suspect you've just got too fine a mesh and may be trying to refine through an adjacent cell.

[vedama]

I'm not sure I understand. Are you saying my background mesh is too fine? My background mesh is supposed to be just the wall boundary of the airfoil. Is my procedure/thought process incorrect? I'm happy to provide more details, if needed.

[Rob]

Can you check the rest of the projection settings? https://ansyshelp.ansys.com/account/Secured?returnurl=/Views/Secured/corp/v212/en/flu_th/x1-100600020.10.1.html Read the Guidelines section here if you don't know how to access help links). It's not a function I use but you could have too fine an inflation for the node move to avoid twisting cells.