trailing edge negative volumes

Nick R · January 19, 2011, 06:46

Hi guys,

I'm trying to mesh an airfoil with a sinusoidal leading edge using a simple blocking scheme with an O-ring. No matter how I move things around I always get negative volumes especially toward the trailing edge (see the images) I tried to get rid of the wedge behind the foil but didn't make much of a difference.
I'm quite a rookie and don't know how to fix these simple things. I'd very much appreciate your help.
Also any ideas about the blocking scheme for a wavy leading edge would be appreciated.
Nick

PSYMN · January 30, 2011, 17:12

I can't see exactly what the problem is, but negative volumes mean that your blocking is probably tangled... Your verts may actually be crossing. Perhaps your upper edge is projected to the lower curve and vice versa?

Perhaps a CGrid blocking would be better than an OGrid.

As for the waving leading edge, with Hexa, you should focus on the topology, not the actual shape. A bent pipe is still a pipe, a wavey wing is still basically a wing. You don't need to block for those curves, just block as a normal wing and associate with the surface. The mesh will follow and interpolate nicely...

Here are some pics...

First the side blocking of the CGRID...
Joel_01.jpg

Then, since this model had a sharp trailing edge, I split behind the wing and collapse the trailing edge block...
Joel_02.jpg

A few more steps and here is roughly done... Note this is just a single wedge block associated with the more interesting airfoil. No extra blocking was done to capture the wavy leading edge.
Joel_03.jpg

The thing about hexa is to have fun with it...

Nick R · February 2, 2011, 02:05

Simon!

This is really cool and sort of like what I made. How did you create the foil? I use Solid Edge. Is there a more efficient way? I had difficulty with creating the surfaces.
Thanks again.

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January 30, 2011, 17:12		#2
PSYMN Senior Member Simon Pereira Join Date: Mar 2009 Location: Ann Arbor, MI Posts: 2,663 Blog Entries: 1 Rep Power: 47	I can't see exactly what the problem is, but negative volumes mean that your blocking is probably tangled... Your verts may actually be crossing. Perhaps your upper edge is projected to the lower curve and vice versa? Perhaps a CGrid blocking would be better than an OGrid. As for the waving leading edge, with Hexa, you should focus on the topology, not the actual shape. A bent pipe is still a pipe, a wavey wing is still basically a wing. You don't need to block for those curves, just block as a normal wing and associate with the surface. The mesh will follow and interpolate nicely... Here are some pics... First the side blocking of the CGRID... Joel_01.jpg Then, since this model had a sharp trailing edge, I split behind the wing and collapse the trailing edge block... Joel_02.jpg A few more steps and here is roughly done... Note this is just a single wedge block associated with the more interesting airfoil. No extra blocking was done to capture the wavy leading edge. Joel_03.jpg The thing about hexa is to have fun with it...

February 2, 2011, 02:05		#3
Nick R Senior Member Nick Join Date: Nov 2010 Posts: 126 Rep Power: 15	Simon! This is really cool and sort of like what I made. How did you create the foil? I use Solid Edge. Is there a more efficient way? I had difficulty with creating the surfaces. Thanks again.