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Old   April 10, 2009, 11:26
Question 2D rotating ellipse (domain interface??)
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Erik Sandstroem
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Hi,

I'm trying to model a 2D spinning ellipse. The model I'm using is a rectangle with 0.3m depth acting as "wind tunnel" and an extruded ellipse (separate mesh) with the same depth.

The ellipse is effectively touching both sides of the tunnel, how do I create an interface between the tunnel and the ellipse in order for it to rotate correctly?

So far I've been able to do a transient rotor stator using the 2 sides of the ellipse to effectively rotate the ball but it doesn't seem to effect the air flow at all, creating streamlines simply go through the ellipse model.

how can i tackle this?

Patrick
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Old   April 13, 2009, 05:50
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Can anyone push me in the right direction for this? Is the current setup valid for creating a domain interface between the two meshes or will I need to alter the mesh somehow?

to reiterate:
wind tunnel mesh has 6 faces
2D ellipse has 3 faces
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Old   April 13, 2009, 21:21
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Glenn Horrocks
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Hi,

I cannot picture what you are describing. Can you draw a diagram?

Glenn Horrocks
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Old   April 14, 2009, 07:19
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Erik Sandstroem
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Not at home currently so don't have the files but I created this in workbench quickly to model the problem.
http://img511.imageshack.us/img511/5188/93505141.jpg

Bear in mind that they are 2 separate meshes in my configuration.

Patrick
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Old   April 14, 2009, 09:09
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Matthias Voß
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hi,
you have to model the ellipse inside a cylinder and define it as the rotating frame.
You will end up with 3 domains.

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Old   April 14, 2009, 10:49
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Erik Sandstroem
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Thanks for the reply.

Could you be more specific in regards to domain interfaces between these 3 domains (ellipse, cylinder, rectangle)?

Patrick
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Old   April 14, 2009, 11:05
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Matthias Voß
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hi,

what you do is setting up a rotating frame which includes the ellipse.
Within the rotating frame you setup everything like you did.A solid/fluid-interface in an rotating frame.
Between the rotating and stationary frame you set up another interface.
Now you could set up the desired spin relatively.
I am not sure about the "windtunnel-walls" in the rotating frame but i think you should set them counterrotating within the rotating frame.Check out the manual on that.

neewbie
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Old   April 14, 2009, 14:36
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Erik Sandstroem
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Right, I think I follow the general layout which can be seen in the image:

http://img21.imageshack.us/img21/674...oglecomcvy.jpg

My problem is which faces do I use for the sides in the domain-interfaces? I've read through countless pages in the manual, searched online and on this forum, tutorials that have domain-interfaces don't seem to work on this comp, so I can't figure out how to create the interface between ball-cyllinder and cyllinder-wall.

Here's my setup so far:
2D ball has 3 faces.. defined as solid domain, stationary
cyllinder has 3 faces.. defined as fluid domain, rotating
fluid-solid interface between the two.. using the outer faces (4) ??

wall has 6 faces.. defined as fluid domain, stationary
fluid-fluid interface between wall-cyllinder... faces?

I'm guessing it's probably something really simple that I'm missing?

Patrick

Last edited by Kambusha; April 14, 2009 at 14:37. Reason: forgot link
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Old   April 14, 2009, 20:26
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Glenn Horrocks
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Hi,

You don't need to model the solid region (which I assume is the ellipse) if you are not modelling heat transfer. If this is the case then you will have two fluid regions, one stationary and one rotating connected by a GGI set to a transient rotor-stator.

Glenn Horrocks
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Old   April 15, 2009, 04:04
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Matthias Voß
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Quote:
Originally Posted by Kambusha View Post
Here's my setup so far:
2D ball has 3 faces.. defined as solid domain, stationary
cyllinder has 3 faces.. defined as fluid domain, rotating
fluid-solid interface between the two.. using the outer faces (4) ??

wall has 6 faces.. defined as fluid domain, stationary
fluid-fluid interface between wall-cyllinder... faces?

I'm guessing it's probably something really simple that I'm missing?

Patrick
hi,
like glenn said: if you donn´t need heattransfer, you don´t have to model the inner part of the ellipse.
so you will need one fluid-fluid interface for the transient rotor-stator-combination.
The walls will be treated as walls as usual.
Maybe i am wrong but you meshed e.g. the tunnel without the rotating frame, right?

neewbie
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Old   April 15, 2009, 05:00
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Erik Sandstroem
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Ok, so I got rid of the solid domain which leaves me now with 2 domains (ellipse and cylinder have been combined as one domain).
Cyllinder is rotating
Wall is stationary
I've tried to create a transient rotor stator interface but I'm obviously using the wrong faces because I keep getting error about the 360 degree tolerance.

http://img16.imageshack.us/img16/9923/cfx.jpg

So I still don't understand which sides to define for the interface.

Patrick
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Old   April 15, 2009, 05:19
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Matthias Voß
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hi,
why is there an ballright/ballleft? Where is the interface in the stationary domain?
You should end up with 7 faces for the tunnel (6 boundaryfaces and the interface(lookslike this is your cyllCIRCLE)) and 4 faces for the rotating domain (2 sideparts touching the tunnelwall, the surface of the ellipse and the interfacesurface which is congruent with the interface within the tunneldomain).

neewbie
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Old   April 15, 2009, 05:52
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Erik Sandstroem
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ballleft and ballright refers to the ellipse sides. ballellipse refers to the ellipse surface, and cyllCIRCLE refers to the cyllinder surface.

Correct me if I'm wrong but this is the setup you're suggesting:
- cylinder + tunnel in one domain (stationary) - the whole cylinder mesh used as side1 for TRS interface
- ellipse in another domain (rotating) - the whole ellipse mesh used as side2 for TRS interface

With this setup though, how do I define the ellipse as a wall without overlapping with interface?

Patrick
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Old   April 15, 2009, 06:00
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Matthias Voß
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hi,
I´m sorry but no.
The ellipse is included in the cylindric domain, which is the rotating domain. This domain in connected via an interface to the stationary one, the tunnel.
Two domains, one interface.
There is no ellipse-sidepart if setup like this.

neewbie
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Old   April 15, 2009, 06:27
Default Frozen Rotor
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Tassi
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Hi

If you want to model a rotating ellipse in a rectangular flow field. Then you ll have to create two domains. A cylinder (encompassing the Ellipse) and a rectangular flow field. The two domains would be joint by a froze rotor interface if it's a steady state simulation and transient rotor if the simulation is transient.

BOL

Tassi
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Old   April 15, 2009, 06:47
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Erik Sandstroem
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Right, I understand the 2 domains 1 interface but like I said before, when defining the interface, I don't know which "face(s)" to use for side-1 and side-2 specifically so the solver keeps ending with errors.

I've defined as transient by the way.

Patrick
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Old   April 15, 2009, 10:26
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hi,
there shouldn't be any problem if you set up proper surface names and the meshes do not intersect.
Side 1 Rotating Domain Interface (Cylinder Surface);
Side 2 Stationary Domain Interface (Cylinder surface included within the Tunneldomain).
Which error do you get and when?
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Old   April 15, 2009, 11:12
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Erik Sandstroem
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I created an additional cylinder for the tunnel domain. Then for domain-interface I've used the cylinder surface in rotating domain and the cylinder surface in tunnel domain like this:
http://img185.imageshack.us/img185/6...ninterface.jpg

Using trans-rotor-stator, I get the following error:

| ERROR #001100279 has occurred in subroutine ErrAction. |
| Message: |
| For domain interface "Domain Interface 1" the pitch angle ratio o- |
| f 1.0000000E+00 does not match the area ratio of 2.- |
| 0120964E+00.

Yours stuck,
Patrick
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Old   April 15, 2009, 18:33
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Hi,

This simulation is a basic application of rotating frames of reference and really is not that hard when you understand the basics. However, explaining what to do on a forum is difficult. Have a look at the tutorial examples which come with CFX using rotating frames of reference, I think there is an axial flow turbine example.

In fact whenever you do a new type of simulation you should look at relevant tutorial examples first to see the basics of how to set it up.

Glenn Horrocks
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Old   April 16, 2009, 00:38
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Hi Erik
Agree with Glenn you can get a better idea after looking in tutorial. Also try using the following settings for you interface
Frame Change/mixing Model : Frozen-Rotor
Rotational Offset : 0 deg
Pitch Change: None
Mesh connection method : GGI

Hope this helps
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