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[ICEM] AHMED with sideplates

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Old   March 13, 2013, 15:27
Default AHMED with sideplates
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Luca
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Hello everyone,
I am trying to mesh an AHMED body with a rear diffuser using the blocks. I have problems to mesh the side plate as in the junction with the body the elements are too deformed. I am not sure if the blocks that I used are fine. I attached a view of the blocks with the zone that I want to mesh as a whole surface, two views of the mesh that I obtained and a view of the mesh that I'd like to obtain. Thanks
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File Type: jpg 3.jpg (101.2 KB, 18 views)
File Type: jpg 4.jpg (23.9 KB, 22 views)
File Type: jpg 6.jpg (45.2 KB, 21 views)
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Old   March 13, 2013, 19:26
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does anyone know how to do it?? I think that I can use in the corner tet elements but I don't know how to do, pls help me because I'm going crazy :S
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Old   March 13, 2013, 20:52
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How did you get the mesh you want to obtain?

Can you do a Y-split (quarter O-Grid) split on the triangular face and propogate it outside of the diffuser?

Stu


P.S. If you are replicating Zhang, he didn't have the bottom corner of the chassis radiused.... ;-)
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Old   March 13, 2013, 21:08
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exatly !! I am working on a project started by Dr. Ruhrmann and supervised by Prof. Zhang..! How do you know it?? Btw I tried to use Y-split but it doens't work (pls see the attachment).

p.s. unfortunately on the thesis there aren't all the dimensions. Maybe do you have the full model??
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Old   March 14, 2013, 05:38
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Easy work to identify, possibly the only one out there using that geometry...!

Think Soso (&Zhang) also used it, but has been retired since!
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Old   March 14, 2013, 05:55
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Soso was an other PhD guy of Sounthampton that worked on a wing in ground effect in generic racing car wake flows. Jonathan Zerihan, Andrea Senior and Andreas Ruhrmann are the people who did the bluff body with diffuser studies while Professor Xin Zhang supervised the projects.
However I managed to solved the problem!!
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Old   March 14, 2013, 05:57
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You forgot to mention Mahon, Bruckner, Molina (all from Soton). Ruhrmann did not do a PhD. Zerihan was only inverted wing in GE not diffuser/inverted ahmed.

By the way I'm a PhD student (Cranfield) doing something similar to Soso, but with a leading F1 car wake and a few more details on the wing...
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Old   March 14, 2013, 09:25
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If you want to mesh the side plate but the back of the car is still sloped up and everything meets at that one point, then you need to have that wedge. The 4th pic you showed wouldn't work unless the car was solidly square at the back, but you still have the ramped up underside, the side plates are triangles...

Instead of the quarter ogrid, I would just use a wedge block... You could also change that wedge block into a swept block if you don't like all the wedges in the same area...
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Old   March 14, 2013, 09:31
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Simon/Luca

The fourth picture is still valid because there is a finite thickness surface between the diffuser and the outside wall. Therefore you can have orthogonal mesh on the outside of the wall and collapse the block on the inside (diffuser section) and split using a quarter O-grid.
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Old   March 14, 2013, 10:23
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OK, if there is a small gap and you are not keeping any mesh in that gap (no solids for CHT), then you can do it.

In that case, block it as if it were a solid square back, then come back and split for the thickness of the plates and delete the block between the plates. Then use bottom up methods to manually create a wedge block from verts (Blocking => Create => From Verticies...) (3D => Degenerate) And select the six verticies.

Then delete the blocks within the plates...


Best regards,

Simon
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Old   March 14, 2013, 11:59
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Simon,

I've tried as you suggested but it doesn't work. In attachment you can see the blocks that I obtain following your method. However if it can help, I tell you that the software automatically cuts the block next to the outside surface of the sideplate (second picture) after the mesh.
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Old   March 14, 2013, 14:06
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Nope, you didn't get what I meant...

Just pretend the back of the car is solid between the plates (from the plate to the symmetry plane)... How would you block it?

Then run some splits through for the thickness of the plates...

Then delete the block between the plate and the symmetry plane.

Up to this point, you have not at all captured the ramp under the back of the vehicle...

Then go and create a degenerate block from 6 verts to capture the fluid region below the ramp...

Then delete the thin blocks within the plates.

Best regards,

Simon
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Old   March 14, 2013, 18:39
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It is also possible to do by splitting off all your blocks and deleting all internal blocks except the diffuser block, then merge the verticies to create a wedge.
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Old   March 14, 2013, 20:40
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Hey Stuart, I see the student has become the master. That is definitely a better way to do it. Not sure why it didn't occur to me.
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Old   March 14, 2013, 20:50
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Thanks a lot Simon!!! Now that I've understood it works perfectly!!!
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Old   March 14, 2013, 21:22
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Quote:
But he still has much to learn, Master. His abilities have made him... well arrogant.
Simon, I think we will still need you for some questions. Sorry for stealing your thunder!
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Old   March 15, 2013, 08:58
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Quote:
Originally Posted by stuart23 View Post
Simon, I think we will still need you for some questions. Sorry for stealing your thunder!
Oh no Stuart, happy to have you on board. Cut in any time.

When I started helping out here years ago mAx was helping the Gambit guys, but there wasn't really anyone helping out on the ICEM CFD side of things. Now there are a decent number of really good and responsive ICEM CFD users. Far has even exceeded my number of posts and he got there in less time.

I am sure the ICEM CFD users around the world appreciate the help they get from you, FAR, DiamondX and others. There also seems to be a good correlation between helping out on CFD Online and ending up working for an ANSYS distributor where you get paid to help people out ;^)
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Old   March 15, 2013, 10:26
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Oh no Stuart, happy to have you on board. Cut in any time.

When I started helping out here years ago mAx was helping the Gambit guys, but there wasn't really anyone helping out on the ICEM CFD side of things. Now there are a decent number of really good and responsive ICEM CFD users. Far has even exceeded my number of posts and he got there in less time.

I am sure the ICEM CFD users around the world appreciate the help they get from you, FAR, DiamondX and others. There also seems to be a good correlation between helping out on CFD Online and ending up working for an ANSYS distributor where you get paid to help people out ;^)
I will never reach your standard and it is for sure. Also I feel that stuart, energy 382, diamondx have better skills than mine.

But I am happy that I have learned alot in very positive and healthy environment and in very less time. I never thought that my efforts would be appreciated that much.
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