Learning Forum

[Mohammadali.nasreddine]

Hello Guys,

I am currently working on my master thesis on VAWT. However, I am facing a problem in meshing a VAWT blades. The mesher is producing low quality elements on the blades called wedges. These result from the inflation layers. 

Attached is a screeshot of the mesh along with the element quality diagram. The green columns are the low quality wedges. Does anyone know how to get rid of these?

Also I attached a screenshot of the inflation layers settings.

Thank you so  much for your help!

[Rob]

Change the quality metric to skewness. Also, if you click on the blue "triangle" on the section plane you'll see whole cells. That makes it easier to see what's going on in the mesh. 

[Mohammadali.nasreddine]

Hello,

I checked all the metrics and they are all below the acceptable ranges.

I just want to know why I am getting these wedges althought I am using a patch conforming method (tetra). Without the inflation layers the quality is so good. When I add the inflation, the wedges appear.

 

 

[Rob]

Please do as I asked. Then pick one of the wedge columns in the graph, you may need to turn off selection planes after that depending on where they're formed. 

[Mohammadali.nasreddine]

Hello Rob,

I did check the skewness as shown in the photos attached.

The first photo is the mesh as is:

The following photos show the elements with high skewness formed around the blade's trailing edge:

Sorry for the late reply

And I appreciate your help!

Thank you

[Rob]

That's the inflation collapsing (stair stepping) at the trailing edge. Skew over about 0.9 or so is high and over 0.95 is too high so needs sorting. If you have a look at the various NACA examples you'll see some approaches to stopping this happening. 

[Mohammadali.nasreddine]

Okay thank you!

Will check that <3

[Mohammadali.nasreddine]

Hello again,
I have a question: is the "element quality" metric important while doing CFD simulations? Or can I just focus on "skewness, orthogonal quality, and  aspect ratio"?

[Rob]

I think "element quality" is mainly Mechanical. For hex & tet meshes I focus on skew and aspect ratio. Ortho quality is also OK for hex & tet but was originally intended for poly mesh.