# Why the noslip doesnbt work

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 August 26, 2008, 02:50 Hi all, I am a newbie of Op #1 New Member   Corenc Join Date: Mar 2009 Posts: 3 Rep Power: 10 Hi all, I am a newbie of OpenFOAM and CFD. I have a question of my first test: I used potentialFOAM to solve a simple channel flow. The slip bounday condition seems work well. Then I change the boundary to no-slip , ie, set the velocity on boundary to fixedvalue zero. Then I get a very strange result. The velocity field is nearly the same as the one of slip condition. I can not see a velocity profile that smoothly ramps down to zero to the boudnaries. Velocity ramps down only in those triangles that has edges (vertieces) on boundaries. So it shoul not be correct. Could you tell me what's the possible reason leading to this error ? Thanks in advance.

 August 26, 2008, 03:37 Potential flows are per defini #2 New Member   Michael Hegetschweiler Join Date: Mar 2009 Location: Zurich, Switzerland Posts: 2 Rep Power: 0 Potential flows are per definition frictionless. Hence, it is not reasonable to define no slip boundary condition at walls (for that you would need wall friction!) So you probably need another way of solving your problem (e.g. k-epsilon with wall function or so) cheers Michael

 August 26, 2008, 03:40 Dear Corenc, you should rev #3 Member   Christian Winkler Join Date: Mar 2009 Location: Mannheim, Germany Posts: 63 Rep Power: 10 Dear Corenc, you should review the physical background of potentialFoam. solving the potential equations requires the flow field to be free of rotation and to have NO friction (no viscosity related effects). Therefore setting a no-slip BC does not make any sense. Best regards Christian

 August 26, 2008, 04:37 Hi,Michael & Christian, thank #4 New Member   Corenc Join Date: Mar 2009 Posts: 3 Rep Power: 10 Hi,Michael & Christian, thank you for your immediately reply. In fact I work in computer animation. I teach Fluid Mechinqiues myself So maybe many erros in the followings... In my understanding, potential flow only requires irrotational. but not non-viscosity. Ok . even it may make no physical sense. Anyway, there is no term of viscosity in the Laplace equation. Why I cant give the no-slip boundary and then solve the laplace? Thanks Thank you.

 August 26, 2008, 04:50 I also tried the case in Fluen #5 New Member   Corenc Join Date: Mar 2009 Posts: 3 Rep Power: 10 I also tried the case in Fluent. And there, I set the viscosity. But I got the same problem as in OpenFoame: non-slip doesn't work. It drives me crazy... Give me some hints, please. -- Corenc

 August 26, 2008, 05:28 Hi Corenc, if you want to s #6 Senior Member   Alberto Passalacqua Join Date: Mar 2009 Location: Ames, Iowa, United States Posts: 1,911 Rep Power: 28 Hi Corenc, if you want to solve a steady, fully developed, channel flow in openFOAM, you might want to try simpleFoam. If you have problems, post the case dictionaries in the forum, so we can give them a look. With kind regards, Alberto __________________ Alberto Passalacqua GeekoCFD - A free distribution based on openSUSE 64 bit with CFD tools, including OpenFOAM. Available as in both physical and virtual formats (current status: http://albertopassalacqua.com/?p=1541) OpenQBMM - An open-source implementation of quadrature-based moment methods. To obtain more accurate answers, please specify the version of OpenFOAM you are using.

 August 26, 2008, 06:15 Hi Corenc, the potential fl #7 Member   Christian Winkler Join Date: Mar 2009 Location: Mannheim, Germany Posts: 63 Rep Power: 10 Hi Corenc, the potential flow is a simplification of the euler momentum balance which is only valid for high Reynolds-numbers. Therefore friction is neglected --> there is no dissipative term which contains viscosity. Regarding physical sense: sometimes there is no way to solve a equation which simply does not describe the physics right ;-) Best regards Christian

 August 26, 2008, 06:39 Dear All I would like to down #8 New Member   Vijayaratnam Piradeepan Join Date: Mar 2009 Posts: 6 Rep Power: 10 Dear All I would like to download OpenFOAM 1.4.1 for 32 bit computer Please let me know, where can I download Thank you Kind Regards Vijay

 August 26, 2008, 07:22 Dear Vijay, please refrain #9 Member   Christian Winkler Join Date: Mar 2009 Location: Mannheim, Germany Posts: 63 Rep Power: 10 Dear Vijay, please refrain from hijacking threads of different topics in the future. Your question has already been answered in this thread: http://www.cfd-online.com/cgi-bin/Op...how.cgi?1/8825 You posted your question there by copying the first post (i do not understand why), so why post it again and again? Download: http://sourceforge.net/project/showf...kage_id=148942 Christian

 August 26, 2008, 07:26 Hi Corenc, here I found a s #10 New Member   Michael Hegetschweiler Join Date: Mar 2009 Location: Zurich, Switzerland Posts: 2 Rep Power: 0 Hi Corenc, here I found a some information about viscous potential flow: http://fluid.ippt.gov.pl/ictam04/tex...FM20_10843.pdf It seems to be a quite unexplored field. But normally potential flow is, as also Christian wrote, inviscous. If you set the viscous term in the momentum equation to zero, you end up with a partial differential equation of 1st order. Thus you can apply only one velocity boundary condition and this would be the impermeability condition. Hope this helps a little more! Michael

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