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Old   January 27, 2011, 05:36
Default Offset of circles, lines, mesh...
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Imagine a circle was drawn with 1m dia. In Autocad, if I use offset command and enter 0.2m value, I will get one more circle with 1.4m dia.

Is there any option like this,...

or one more example: a line was drawn at 70 deg angle to the horizontal. I need one more line parallel to the original at a distance of 8mm. And the second one also, to be in the same angle.

1. Mesh: Meshing I have to do for volumes, surfaces and edges or only volume is enough?

2. how to split volume into logical volumes?

3. I have two options, one is tetra hydral and hexogonal... Which is
better?

4. How to select sources for doing meshing? Anu specific criterion like selecting edges or surfaces?

Thanks in advance...
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Old   January 27, 2011, 05:55
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face/copy, there is an option "scale"
Your second example is just a copy with translation (edge/copy)
1. you can direct mesh the volume
2. by creating a surface, you can cut your volume with this surface (-->split)
3. you have more than 2 options:
*full tetra
*tetra hexcore (fill your domain with hexa in the core)
*hexa-map (outer surface with quad)
*hexa cooper (sources meshed with quad-pave)
etc...

You may decide what kind of mesh you want.
If you don't have time for very nice full hexa mesh, I would advice tetra-hexcore in combination with size fonction for local refining
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Old   January 27, 2011, 09:16
Default Fan Simulation
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Hi Max,

As I told earlier, I have 2 volumes.

1) Solid - Rotating part.

2) Fluid - Stationary part.

When I browsed through some threads, i saw: There should be sepearte mesh for below problem.

VAWT transient cfd problem

1) Whether I have to proceed in the same way?... As the interface between solid and fluid will change continuously....

2) Whether my problem will come as dynamic mesh...like in combustion engine.

3) What type of condition i have to give so that whole solid assembly should rotate at some rpm?

Please guide me...
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Old   January 27, 2011, 09:44
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They separate volumes for computing a sliding Mesh.
Rotor FLUID volume rotates since stator FLUID volume is stationnary.
The limit between the two domains is defined as Interface.
But you need to substract your fan.
1),2),3) --> don't jump so quickly in moving mesh.
Try first a steady one, and then go to moving mesh
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Old   February 25, 2011, 07:56
Default Meshing for rotating frames
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Hi Max,

after a long time. I had problem with meshing. I tried to solve example in Fluent 6.3 version tutorial - "multiple rotating reference frame models". And example outlined is "centrifugal fan-2d".

There are 3 fluid zones. Fluid one is outer casing, fluid -2 is blades portion (Which is rotating), fluid-3 is close to inlet or center. Please find the first figure for overall picture.

full mesh fan.jpg

In the next figure, A closure snap was taken, where mesh nodes are same at interfaces for fluid zone.

case-1 closure grid.jpg

Problem:

But, When I tried to model, for opposition rotation of blades. i.e. middle fluid volume containing blades mirror about vertical. and tried to do meshing. Now, I am getting different grid points at boundary.

case-2 closure grid.jpg

One more thing: as middle fluid volume is rotating reference frame, the interfaces (Describled as wall in gambit) with other faces i have convert into interior type in fluent. there are 2 walls. Let's say wall-1 and wall-2.

I have to match grid points at the interfaces. As, when export it to fluent, it will create wall-1 shadow, and wall-2 shadow as these are seperated by fluid volumes.

But, if the above mismatch is happening shadow items are not created. inturn iam not able change boundary conditions in fluent from wall --> interior. I am not getting that option at all... I found this is due to meshing mismatch at interfaces of different fluid volumes.

May I know how to match.
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Old   February 25, 2011, 09:27
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your fluid zones don't have to match since your rotor will rotate.
In other words your rotor zone should be disconnected to other fluid zones.
After disconnecting you should be able to move your rotor zone without error (no link with other geometry)
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Old   February 25, 2011, 10:00
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Max,

My rotor zone is seperate only. My problem is with meshing...

Fig: 1: contains center mesh: 25 interval size, tri and pave mesh.

middle one: rotor portion: 50 interval size, tri and pave mesh.

outer one: 100 interval size, tri and pave mesh.

If you observe closely in Fig.2...

grid nodes of rotor fluid volume and outer volume are connecting at interface.

similarly for the rotor volume and inner volume.

But, where as in fig:3 (Reverse direction of rotation):

inner volume and rotor volume grid points are connecting. where as it is not for outer and rotor volume.

I want to mesh such away that the second case grid points also match at interface (i.e, outer and rotor volume). What procedure i have to follow to match the points... how to get that type of grid pattern...

hope this understands:
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Old   February 25, 2011, 10:05
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I don't understand:
you want disconnected zones, where meshes are matching together at interfaces?
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Old   February 25, 2011, 10:21
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Please see Fig:2: There are 3 different meshes. top one is: 100 interval size, inner one: 50...

mesh elements in rotor fluid are varying in size from outer (bigger) to inner (smaller).

similar case for inner fluid also.

Where as in fig:3, with same mesh specifications.

mesh elements in rotor volume are of equal size. but, inner one are vaying in size.

i would like to have mesh elements in varying in size for the rotor fluid also.

Hope this helps...
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Old   February 25, 2011, 11:13
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you want your rotor mesh having mesh gradient (from fine: inner to coarse: outer)?
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