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Resolving aerofoil tip curvature in CFX-mesh

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Old   September 30, 2007, 08:06
Default Resolving aerofoil tip curvature in CFX-mesh
  #1
Jenny
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Hi,

I recently posted a query about negative pressure I was calculating in the run of a fan and have since resolved this problem, so thank you to the folk who responded to me.

I have since been trying to refine the mesh for further analysis and come up with a problem which I am hoping someone may be able to suggest an answer to. To explain the setup:

1. I have a hollow cylinder with a small chamfer on the top and a closed top which acts as a hub. In reality it is pressed onto a motor, hence the hollow inside. On the straight walls of the cylinder, again in reality, are glued a set of vanes. My CAD model was set up so the cylinder and blades were one unit. For the numerical work in CFX, I extruded the top of the hub to the bottom to basically fill it up, so the whole geometry was a closed surface.

2. Where the vanes are glued to the side of the cylinder, the contact area is in the shape of an aerofoil section. I am having untold difficulty in resolving the curvature at the top of the aerofoil shape. I've tried face spacing control on the cylinder, point control and line control with numerous edge lengths and radii. For some reason the mesh keeps cutting off the edge of the aerofoil tip and going back onto itself so I get errors related to the mesh intersecting and overlapping itself, or another about negative parametric volumes.

I am using CFX mesh and my mesh is composed of tets. I am trying to put inflation layers on the walls of the cylinder and vanes, but at this stage can't even get the surface mesh to work.

I have put up an image trying to show where the problem is occurring. I have circled in white the problem area. http://www.dezignit.com/hubproblem.jpg

I've exhausted everything I know to solve this and I'd appreciate any bright ideas anyone might have on a way to resolve this problem.

Best wishes, Jenny
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Old   October 1, 2007, 18:22
Default Re: Resolving aerofoil tip curvature in CFX-mesh
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Glenn Horrocks
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Hi,

What meshing package are you using? This type of mesh is probably best done with a hex grid, so ICEM-hexa would be a good choice.

Glenn Horrocks
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Old   October 1, 2007, 18:26
Default Re: Resolving aerofoil tip curvature in CFX-mesh
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Jenny
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Hi Glenn,

I'm using CFX-mesh and due to the shape of my blades and the whole domain I can only apply a tet mesh. Unfortunately it's not a sweepable geometry and the engineers I spoke with at CFX confirmed this.

I've tried to simplify it using virtual topology, but it comes up with more problems.

It seems to work OK with a coarse mesh, but as soon as I try and refine it and put controls around the leading edges and tips of the blades, I run into this overlapping mesh problem.

Jenny
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Old   October 2, 2007, 11:51
Default Re: Resolving aerofoil tip curvature in CFX-mesh
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Erich
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Are you using the Relative Error Option under face spacing? Sometimes changing from Delaunay to Advancing front surface meshing or definitely the mesh spacing can address mesh errors.

Good luck!

Erich
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Old   October 3, 2007, 05:55
Default Re: Resolving aerofoil tip curvature in CFX-mesh
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Sans
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I think you have tried mesh spacing. But is your leading edge a separate face or surface? If yes try a finer mesh control only on that face. CFX Mesh usually does that pretty well.
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