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Old   July 7, 2011, 10:08
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Chris Sideroff
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Eren10 can you post of picture of what you're trying to do to help me understand? I might be better able to give you proper guidance this way.

Thanks, Chris
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Old   July 7, 2011, 10:34
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Originally Posted by cnsidero View Post
Eren10 can you post of picture of what you're trying to do to help me understand? I might be better able to give you proper guidance this way.

Thanks, Chris

I have attached a view of what I was trying to do. You can see that there are 2 domains, with overlapping region. This domains should fit at that section.
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Old   July 7, 2011, 10:38
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Eren10 to get the extrusions to match you need to extrude from all the airfoil connectors simultaneously. To do so, select all the airfoil connectors then perform the extrusion (Create > Extrude > Normal ...).

You may need to take some precautions near the trailing edge but I can't see the detail there. Is it blunt or sharp?
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Old   July 7, 2011, 10:59
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It is sharp. I have created a lot of meshes with the method u said. but this way I have not much control over yplus values, but it is oke.

If it is possible I would save the BoundaryConditions once, else I have to type it again, I am using the geometry for different simulations.

And a last question: Is there a general function that will improve the meshquality after the mesh is generated ?

Last edited by Eren10; July 7, 2011 at 11:14.
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Old   July 7, 2011, 11:26
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Ziad Boutanios
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You can still have very good control over the Y+ values by doing it the way Chris advised. It is better to use several connectors on the pressure and suction sides, and then extrude from them all simultaneously. Your mesh will be much smoother and will not overlap.

As for mesh quality tools, you can use the elliptic solvers that come with the structured blocking tools. The default settings should be pretty good for this.

If you run into problems at the trailing edge, build a connector there that is approximately normal to the two surfaces of the airfoil and then extrude along this connector normal to the airfoil surface. Once done, you can then extrude this connector downstream to create your wake region.
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Old   July 7, 2011, 11:28
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Quote:
Originally Posted by Eren10 View Post
It is sharp. I have created a lot of meshes, the last what I have asked was to have control over the yPlus values because I am using wallFunctions.

If it is possible I would save the BoundaryConditions once, else I have to type it again, I am using the geometry for different simulations.
It's not clear to me what you trying to accomplish - I am sorry for that. From the picture you attached it looked like you creating an extrusion for each connector ... ahhh, I know what you are trying to do now. You want the near wall spacing to vary along the length of the airfoil.

As you've found out, you can only specify one delta_s when creating an extrusion but there is a way to achieve what you're looking for. First, split the airfoil surfaces at one or more locations, e.g. 50% chord. I see you've done it on the suction side so do the same on the pressure side.

Now create the extrusion with all the connectors. So select them all then Create > Extrude > Normal ... You should now see the Assemble panel. Before clicking Done, in the Assemble Special frame, click Delete All Edges, change the Assemble Type to One Edge Per Connector, click Assemble and then click Done. Perform the extrusion as previously.

You'll notice now that one domain will be created from each connector and there are connectors emanating from the split points in the middle of the airfoil. Using Grid > Distribute you can modify the end spacing and distribution on these connectors to achieve the spacing you want at each location. For example, when I tried it I found that when I modified the spacing I had to also change the distribution function of the connector to Geometric.

The tricky part in the doing the above is that its most likely going to disturb the internal grid lines created the hyperbolic extrusion. You can remedy this by running the domains in the elliptic solver. Pick the domains, Grid > Solve ... and run the solver for 20-30 iterations.

I went through this procedure myself on a NACA4412 with C = 1. I split the airfoil at ~40% on top and bottom. I created a One Edge Per Connector extrusion (as outlined above) with ds = 0.0001, GR = 1.2 and 30 layers. I then change the middle normal connectors wall spacing to 0.0004 and distribution to Geometric. I did the same for the normal connectors at the trailing edge but with ds = 0.0008. I then ran the domains through elliptic solver for 30 iterations with default settings.

See the result in the attached image. It's a bit tough to see but you can make out the expanding BL near the TE.

Let me know how it goes, Chris
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Old   July 7, 2011, 11:30
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Quote:
Originally Posted by ziad View Post
You can still have very good control over the Y+ values by doing it the way Chris advised. It is better to use several connectors on the pressure and suction sides, and then extrude from them all simultaneously. Your mesh will be much smoother and will not overlap.

As for mesh quality tools, you can use the elliptic solvers that come with the structured blocking tools. The default settings should be pretty good for this.

If you run into problems at the trailing edge, build a connector there that is approximately normal to the two surfaces of the airfoil and then extrude along this connector normal to the airfoil surface. Once done, you can then extrude this connector downstream to create your wake region.
Sorry Ziad, you replied before I could finish my long explanation ;-). Thanks for your help.
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Old   July 7, 2011, 11:37
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Originally Posted by cnsidero View Post
Sorry Ziad, you replied before I could finish my long explanation ;-). Thanks for your help.
Don't worry about it

BTW I don't think it is necessary to have such tight control over the normal spacing to the wall to achieve a good Y+. If Eren is using RANS with the usual wall function recipes he will need to have 30 <= Y+ <= 150 and this will give a comfortable margin of wall spacing to use.

Another way of doing this would be creating one connector at the TE and then extruding it along the pressure and suction sides, followed with a healthy elliptic solver dose...
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Old   July 8, 2011, 06:03
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Originally Posted by cnsidero View Post
I created a One Edge Per Connector extrusion (as outlined above) with ds = 0.0001, GR = 1.2 and 30 layers.

To vary the yPlus values I should be able to change the y distance to the first cell. With the procedure you explained this can't.

I am trying to reduce simulation error as far as I can. Anyway, I will continue with the one normal extruded mesh.

Thank you Chris and Ziad.
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Old   October 26, 2011, 06:32
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I have a question about the function " solve " in Pointwise. I think this can be done after mesh is generated. Wat is its function ? Shall the mesh quality improve ?

Regards.
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