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-   -   wing with sharp trailing edge mesh through extrusion (https://www.cfd-online.com/Forums/pointwise/113544-wing-sharp-trailing-edge-mesh-through-extrusion.html)

Hybrid February 21, 2013 13:16

wing with sharp trailing edge mesh through extrusion
 
How can I extrude a wing having sharp trailing edge?

I have come to know that by adding wake domain, the select wing domains and wake domain and extrude all of them at once. By doing so, I get a mesh with wing domains (upper and lower) extruded up and down while wake domain extruded only in one direction.

How can I get the wake domains extruded on both sides?

If one can try, can assume any wing with sharp trailing edge.

jchawner February 24, 2013 17:25

I'm going to attempt an answer without actually trying it myself first. When you define the initial face from which extrusion will begin (clockwise: wake, lower wing, upper wing, wake) you have to select the wake domain twice.

Hybrid February 25, 2013 10:38

I tried this but I am not able to select a domain twice in Pointwise. You can try using any generic wing with a sharp trailing edge. I wand to use NORMAL extrusion.

jchawner February 25, 2013 10:50

That's the danger of me answering without trying it myself. At this point your best bet is to contact our tech support team directly at support@pointwise.com.

cnsidero February 25, 2013 23:34

1 Attachment(s)
Ali,

The trick to getting this to work is to assemble the face manually. If your mesh, for example, had three domains (one for lower wing, one for upper wing and one for the wake) choose all three and select Create, Extrude, Normal ...

In the Assemble panel, check the Assemble Special box to expand the panel. Now click Delete All Faces to restart the face assembly process and uncheck Domain Once to allow selection of the wake domain more than once. Starting with the wake domain, pick the domains in successive order (e.g. wake, upper surface, lower surface, wake again).

When you select the wake domain again, you will be presented with the linkage assembly diagram and a list of domain-face linkages. You need to choose the linkage at the trailing edge of the airfoil. Click Use Selected Link, click Save Face and click Done. It's important to follow these steps exactly. If you did you should be in the usual Extrusion mode and the extrusion will march off of both sides of the wake domain (you should see arrows pointing from both sides).

Let me know if you get it working, Chris

Quote:

Originally Posted by Hybrid (Post 409360)
How can I extrude a wing having sharp trailing edge?

I have come to know that by adding wake domain, the select wing domains and wake domain and extrude all of them at once. By doing so, I get a mesh with wing domains (upper and lower) extruded up and down while wake domain extruded only in one direction.

How can I get the wake domains extruded on both sides?

If one can try, can assume any wing with sharp trailing edge.


Hybrid February 26, 2013 14:39

Thanks Chris Sideroff. It works really great.

Now a new problem, how to control the quality...extrusion fails after 3,4 steps. Sometime extruded root and tip airfoil connectors deshaped.

How can i get a nice mesh with minimum skewness and orthogonal?

How to check orthogonality in Pointwise?

cnsidero February 26, 2013 19:39

Ali,

By default, the normal extrusion only checks for negative Jacobians (aka cells with negative volume). There is additional cell quality checking you can monitor during the extrusion.

Back to your difficulty getting the extrusion to proceed. My first suggestion, and something I always watch for is mis-matched spacings in the domains of the starting face. Using my simple 3D airfoil as an example, I made sure the streamwise spacing at the trailing edge of the wing was the same as the streamwise spacing of the wake domain. This is particularly important when extruding from concave (i.e. internal) corners.

The next suggestion is to keep the initial normal spacing (init ds) about 4-6x smaller than the smallest transverse spacing in the domains of the starting face.

My last suggestion is to turn down the volume smoothing parameter to a small value (e.g. 0.05) until the extrusion proceeds away from the wall at least one BL thickness. Volume smoothing controls how much the algorithm smooths the extrusion front and I find, for tougher extrusions, the default value of 0.5 is too high. You can turn it back up once the extrusion gets away from the wall.

These are my general suggestions. If they still don't work, you're going to have to at least post a picture of your mesh so I can give more specific advice.

-Chris

Quote:

Originally Posted by Hybrid (Post 410254)
Thanks Chris Sideroff. It works really great.

Now a new problem, how to control the quality...extrusion fails after 3,4 steps. Sometime extruded root and tip airfoil connectors deshaped.

How can i get a nice mesh with minimum skewness and orthogonal?

How to check orthogonality in Pointwise?


taxalian March 3, 2013 17:07

Hi Ali,
See my reply to the other message "[Pointwise] Boundary layer mesh" posted recently, hopefully that might also be helpful to you.

good luck.

Hybrid March 18, 2013 17:17

Quote:

Originally Posted by cnsidero (Post 410071)
Ali,

The trick to getting this to work is to assemble the face manually. If your mesh, for example, had three domains (one for lower wing, one for upper wing and one for the wake) choose all three and select Create, Extrude, Normal ...

In the Assemble panel, check the Assemble Special box to expand the panel. Now click Delete All Faces to restart the face assembly process and uncheck Domain Once to allow selection of the wake domain more than once. Starting with the wake domain, pick the domains in successive order (e.g. wake, upper surface, lower surface, wake again).

When you select the wake domain again, you will be presented with the linkage assembly diagram and a list of domain-face linkages. You need to choose the linkage at the trailing edge of the airfoil. Click Use Selected Link, click Save Face and click Done. It's important to follow these steps exactly. If you did you should be in the usual Extrusion mode and the extrusion will march off of both sides of the wake domain (you should see arrows pointing from both sides).

Let me know if you get it working, Chris


Thanks All who reply the post.

It works but need more practice and experience on Extrusion especially Normal Extrusion.

AhmedSaad February 8, 2017 19:16

Hello Ali!
I wonder if you already figured out what causes mesh extrusion to fail and why leading and trailing nodes sometimes dislocated.

jchawner February 9, 2017 09:23

Ahmed, extrusion can fail for many reasons depending on which extrusion method you're using, the complexity of your geometry, the quality of the initial mesh, and more. I also don't know what you mean by dislocated.

AhmedSaad February 9, 2017 10:28

5 Attachment(s)
Thanks for your reply John,

I attached photos for my blade surface mesh and its minimum included Angle. When I do create, extrude, normal, I receive different errors in the first extruded step, sometimes due to some cells met the negative skew jacobian stop conditions or min positive skew jacobian.
I kept that 1st step mesh and attached photos if the created negative volumes at the root and tip of the blade. (Note: here the deformation happened in the trailing edge, In other cases I've tried, the deformation happened in the leading edge)

I tried the suggestions made by Chris and what I found in another thread but with no solution.
I think my problem within the tolerance but I am not sure. I had set an appropriate model size tolerance (as I believe) and re-import my geometry but it didn't work too.

I hope someone defines my problem.

Best Regards,
Ahmed

jchawner February 9, 2017 10:32

No images were attached. And I caution you against jumping immediately to the conclusion of tolerances.

Extrude, Normal and the fact that you're using Jacobian as a stop condition tells me you are extruding quads (if 2D) or hex (if 3D). If true, change the two Kinsey Barth smoothing factors to 3.

Look at your initial mesh and make sure that there are no large cell-to-cell jumps in cell size.

AhmedSaad February 9, 2017 10:33

4 Attachment(s)
attached the remaining photos

AhmedSaad February 9, 2017 10:34

Sorry I edited my reply and attached the photos

AhmedSaad February 9, 2017 10:38

I changed the two Kinsey Barth smoothing factors to 3, and still have the same problem.

jchawner February 9, 2017 10:39

A quick look at your images tells me the problem is at the sharp trailing edge where the extrusion direction is probably undefined (i.e. what is the normal direction to a singularity?) Because I think you're trying to extrude an O-grid topology around the airfoil.

It also looks to me as though the trailing edge is doubly defined (i.e. there are two connectors there). This means that topologically the airoil looks like an open sheet to the extruder. That initial domain must use only 1 connector at the trailing edge.

You might also consider putting a connector at the leading edge and using that as the seam instead of the trailing edge. That's a trick, but it might help.

And you might want to think about using a C-grid topology to "hide" the sharp trailing edge. Add a domain that attaches to the trailing edge and extends downstream. It will be part of your initial mesh along with the upper and lower surface of the airfoil.

Good luck.

AhmedSaad February 9, 2017 11:19

5 Attachment(s)
As I understood,
First, the O-grid topology around airfoil requires to define the normal extrusion direction of the trailing edge. How can I define it? and How it works in this video?:
https://www.youtube.com/watch?v=KOvWlgBEzo4&t=1174s
Attachment 53871

Second, I checked the trailing edge connector and as it seems in the merge panel in the picture attached, it is not red.
and after I re-extrude in normal direction this time. I got a deformation in leading edge. And at the trailing edge after extrusion, It seems doubled as you mentioned.


Third, C-grid would be helpful but I don't know how to create a wake domain attached to the trailing edge (different pitch angles along the spanwise direction) Do you have any suggestions?

jchawner February 9, 2017 11:31

Your case probably requires the assistance of our Technical Support team. Email your Customer ID to them at support@pointwise.com and share this information you've showed me. Best Regards.


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