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-   -   What boudary conditions should I use (http://www.cfd-online.com/Forums/openfoam-solving/59139-what-boudary-conditions-should-i-use.html)

lakeat February 9, 2008 04:09

A small question, I just pe
 
A small question,

I just performed a cylinder flow with icoFoam, but the result seems to be different from those in ferzifer's book. So i am wondering what might be wrong.

How to set upper and lower boudaries conditions?

wall or cyclic, Any ideas? Thanks a lot.

Because I am afraid if I use wall patch when Re is high, the mesh will be very expensive. I saw some paper used cyclic though in fact it is actually another problem.

Daniel

mike_jaworski February 10, 2008 01:53

Hi Daniel, This question s
 
Hi Daniel,
This question seems far too general to be answered in any sort of detail. Maybe you could tell us *how* the solution is different and compared to what? An analytical solution? another simulation? experiment?

Also, have you done the potentialFoam tutorial? It's detailed in the Programmer's guide and covers a cylinder in cross-flow. Maybe that would be a good place to start and see how BCs are set there.

Good luck,
Mike J.

lakeat February 12, 2008 04:16

I am making my effort to simul
 
I am making my effort to simulate the case cylinder flow as described in "Computational Methods for Fluid Dynamics" Chapter 8, and I hope to get a better understanding of liftDrag (for my ultimate aim to to simulate drag reduction).

The geometry is the same as Ferziger's.
I meshed with gmsh, and then used gmsh2ToFoam.
Re is 20,40,100,150.
fvSolution and fvScheme are the same as those in icoFoam/cavity, and are not changed.
I lowered the 1st cell hight to satisfy y+=1.
The velocity profile, I used both the parabolic one and the uniform one.
One thing I'm not sure is the upper and lower wall boundary condition, which type should I set?

whatever, the variation of CD on a cylinder is very smooth on the book of Ferziger, however, mine is not smooth at all!
http://www.cfd-online.com/OpenFOAM_D...ges/1/6654.gif
meanwhile, the meanvalue is too small.
Here is Prof. Ferziger's
http://www.cfd-online.com/OpenFOAM_D...ges/1/6655.gif

Hi Mike, thank you,
I noticed in potentialFoam tutorial, the BC is symmetryPlane. But how about cyclic? Will the result be of great defference?

lakeat February 12, 2008 04:20

I'm still very new to CFD. Co
 
I'm still very new to CFD.
Could anyone point out what's going wrong here, thanks.


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