# What boudary conditions should I use

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 February 9, 2008, 04:09 A small question, I just pe #1 Senior Member     Daniel WEI (老魏) Join Date: Mar 2009 Location: Beijing, China Posts: 689 Blog Entries: 9 Rep Power: 14 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 __________________ ~ Daniel WEI ------------- Boeing Research & Technology - China Beijing, China Email

 February 10, 2008, 01:53 Hi Daniel, This question s #2 Senior Member   Michael Jaworski Join Date: Mar 2009 Location: Champaign, IL, USA Posts: 126 Rep Power: 10 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.

 February 12, 2008, 04:16 I am making my effort to simul #3 Senior Member     Daniel WEI (老魏) Join Date: Mar 2009 Location: Beijing, China Posts: 689 Blog Entries: 9 Rep Power: 14 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! meanwhile, the meanvalue is too small. Here is Prof. Ferziger's Hi Mike, thank you, I noticed in potentialFoam tutorial, the BC is symmetryPlane. But how about cyclic? Will the result be of great defference? __________________ ~ Daniel WEI ------------- Boeing Research & Technology - China Beijing, China Email

 February 12, 2008, 04:20 I'm still very new to CFD. Co #4 Senior Member     Daniel WEI (老魏) Join Date: Mar 2009 Location: Beijing, China Posts: 689 Blog Entries: 9 Rep Power: 14 I'm still very new to CFD. Could anyone point out what's going wrong here, thanks. __________________ ~ Daniel WEI ------------- Boeing Research & Technology - China Beijing, China Email

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