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-   -   Boundary Conditions. Simulation cylinder. (http://www.cfd-online.com/Forums/openfoam-solving/79928-boundary-conditions-simulation-cylinder.html)

davidmd September 8, 2010 13:26

Boundary Conditions. Simulation cylinder.
 
Hello! I just started with OpenFOAM.
I use version 1.7.0. I'm trying to simulate a cylinder in which the laminar (or turbulent) incompressible fluid flow.
And the bottom of the cylinder rotates. Like this:

http://davidmd.narod.ru/cyl.png

What is the boundary condition I set on the bottom and how to do it?
I would be grateful for any assistance conditional. Maybe someone has already done this?
Sorry for my English:)

A! And what solver shall i use?

davidmd September 11, 2010 12:30

Surely no one can help? It's very, very important to me, please...

maddalena September 17, 2010 08:42

Hi David and welcome! Hope to be not too late...
Quote:

Originally Posted by davidmd (Post 274485)
what solver shall i use?

Everything depends on what simulation you want to perform. I guess you want a steady state laminar or turbulent simulation. In that case I would use simpleFoam.
Quote:

Originally Posted by davidmd (Post 274485)
And the bottom of the cylinder rotates. What is the boundary condition I set on the bottom and how to do it?

If you wants that the cylinder bottom is the only rotating surface, than I would apply a rotatingWall BC. Search in the forum for the way to apply it.
Enjoy

mad

davidmd September 19, 2010 10:04

Thank you very much, maddalena, I built something like the geometry and boundary conditions, but I used iсoFoam not simpleFoam. What is the difference between them?
I apologize for maybe a stupid question. I just sooo hard to read literature in English :(

ata September 20, 2010 03:01

simpleFoam v.s. icoFoam
 
Hi David
How are you? I hope you are doing very well.
As you can see in the source of the solvers icoFoam is a transient solver for incompressible, laminar flow of Newtonian fluids and simpleFoam is a steady-state solver for incompressible, turbulent flow.
Good luck
Best regards

Ata

davidmd September 23, 2010 08:42

Now I'm faced with this problem. I can not define the boundary condition at the upper edge of the cylinder (i mean the top sureface of my fluid). Maybe someone knows how to do this? Uz = 0, dUx / dx = 0, dUy / dy = 0

davidmd September 23, 2010 08:47

Hi, ata!
Thank you for help, I hope you are all well too!
davidmd

davidmd September 23, 2010 10:14

I'm trying to simulate simple mixer. It looks like cylinder with rotating bottom and open top filled with fluid. The other cylinder is inserted into the first.
So something like this:
http://davidmd.narod.ru/WIREFRAME2.png


http://davidmd.narod.ru/WIREFRAME.png


http://davidmd.narod.ru/SUREFACE.png

So, on the walls of this cylinders i set the fixedValue BC On the bottom - rotatingWallVelocity.
And to top I want to set the boundary condition such as on the surface of the liquid ... At first I tried to do zeroGradient boundary condition. But then it turns out like this:
http://davidmd.narod.ru/YZ_PLANE_FLOW.png

It turns out that the fluid enters the center and comes out at the edges, but this is not correct.
I thought that it was possible to establish a boundary condition like Uz = 0 Ux = dUx / dx Uy = dUy / dy

Maybe i need another BC... I don't know. The main thing that it was just on the surface of the liquid.

Once again: sorry for my English :-)

maddalena September 23, 2010 10:48

Mmm...
I am still confused by your geometry...
there are two cylinders, one inside the other, filled with fluid. The external one has a rotatingWall BC, while the internal one is fixed. The bottom of the internal cylinder is open. You want to study the effect of the bottom surface rotation of the external cylinder into the fluid. Am I right?
What about your pressure BC?
As a first idea, I would use an inletOutlet BC for U and a fixedValue for p. But not sure about that.

mad

davidmd September 23, 2010 14:34

maddalena, you are right!
My preasure BC is set to fixedValue and it is 0...

maddalena September 23, 2010 15:16

So, this is fine:
Quote:

Originally Posted by davidmd (Post 276386)
My preasure BC is set to fixedValue and it is 0...

if you fix pressure, you cannot fix velocity, and your gradient should be specified instead. I would use an inletOutlet with an inletValue (0 0 0): it will behave as a fixedValue on the inner cylinder and as a zeroGradient on the fluid between the two cylinder.
what you think about that?

mad

davidmd September 24, 2010 03:33

You mean the boundary condition inletOutlet with inletValue (0 0 0) on the upper surface of the cylinder?

maddalena September 24, 2010 03:57

Quote:

Originally Posted by davidmd (Post 276449)
You mean the boundary condition inletOutlet with inletValue (0 0 0) on the upper surface of the cylinder?

Yes, that one. Please report if you have different ideas or if you can find a solution.
cheers

mad

davidmd September 24, 2010 11:52

Quote:

Originally Posted by maddalena (Post 276450)
Yes, that one. Please report if you have different ideas or if you can find a solution.
cheers

mad

Wow! It works exactly as I have! :) maddalena, thank you very much! It's great!!! :) I never would have guessed! :-)

maddalena September 26, 2010 07:44

Quote:

Originally Posted by davidmd (Post 276546)
Wow! It works exactly as I have! :) maddalena, thank you very much! It's great!!! :) I never would have guessed! :-)

That is nice! Happy to be useful!
Cheers

mad

T.D. October 6, 2010 09:42

cylindrical shapes
 
Hi guys
since you worked with cylindrical shapes i thought you might help me please

i need to do a flow between two parallel disks the bottom is stationary and the on eon top rotates with a certain omega.

How to draw?

Help please, and what about the BCs?

thanks a lot

davidmd October 6, 2010 14:49

Hi, T.D.!
I don't understand your geometry :)
maybe you can draw it? :)
It's very difficult to me to wrote on english :)

T.D. October 6, 2010 17:15

Drawing attached
 
1 Attachment(s)
hi
this is the drawing attached

thanks a lot

davidmd October 6, 2010 18:31

i'm not sure, but you probably should use BoundaryFOAM
And create such a geometry will be no problems. If you want me to send you an example of my case with rotating bottom. But you have to fundamentally alter it. :)

ata October 7, 2010 02:33

Hi T.D.
How are you brother? I hope you are doing very well.
May be you can use gambit for mesh generation.
Good luck
Best regards

Ata


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