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-   -   How to Apply Rotational Wall BC (http://www.cfd-online.com/Forums/cfx/105232-how-apply-rotational-wall-bc.html)

tango711 July 25, 2012 18:27

How to Apply Rotational Wall BC
 
3 Attachment(s)
Hello all,

I am attempting to apply a rotational wall boundary condition to a certain domain but when I do I get an error which says:

| ERROR #002100080 has occurred in subroutine CHECK_NORMV.
| Message:
| The specified velocity vector on the boundary patch
|
| Boundary 3
|
| has a significant normal component at one or more faces. One of
| these face locations is
|
| (x,y,z) = ( 1.53317E-01, 3.92873E-02, 1.37851E-02).
|
| The angle between the specified velocity and the element surface is
| 87.996 degrees at this face. This is considered an error because
| it implies that the mesh is moving. The following are possible
| reasons for the error message:
| 1. There is a setup error; for example, an incorrect axis of
| rotation.
| 2. There may be a meshing problem; for example, the nodes on a
| rotating surface might not lie on the surface of revolution.
| 3. The boundary is curved and the mesh is very coarse. In this
| case, you may modify the tolerance by increasing the
| expert parameter 'tangential vector tolerance wall'
| from its default of 20 degrees.
+--------------------------------------------------------------------+


I have attached pictures of the troublesome part of the domain I am using. I think it is because there is a wall which is radial, thus the tangential vector would be normal to it (The angle given is almost 90 degrees in this case, I am not sure if I can change the expert parameter to that much), how can I solve this?

I double checked and I am sure that the axis of rotation is correct and that the mesh quality is fine.

Best regards,

Tango

flotus1 July 26, 2012 01:51

There is a reason for the "low" tolerance angle between wall velocity and wall direction.
Running the case with a rotating wall boundary condition while some parts of the wall are not tangential to the velocity components makes no sense.
The walls would have to move through the fluid domain, which they can't unless you use a moving mesh or some kind of rotor-stator setup.

BTW: there are many more parts of the suface which point into the tangential direction of the rotation you are trying to apply.

tango711 July 26, 2012 12:34

Quote:

Originally Posted by flotus1 (Post 373611)
There is a reason for the "low" tolerance angle between wall velocity and wall direction.
Running the case with a rotating wall boundary condition while some parts of the wall are not tangential to the velocity components makes no sense.
The walls would have to move through the fluid domain, which they can't unless you use a moving mesh or some kind of rotor-stator setup.

BTW: there are many more parts of the suface which point into the tangential direction of the rotation you are trying to apply.

Thank you Alex,

In that case, do you think that if I make that whole domain rotating, and apply a counter rotating wall BC on the outside wall, that this is solve my problem?

Would the fluid flow be sufficiently similar to what I was trying to do?

Thanks again,

Tango

flotus1 July 26, 2012 14:27

In general, rotating the part or the domain are not the same.
It is impossible for me to judge whether the error is neglectable in your case.
I don't know enough about your setup and about rotating domains.


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