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-   -   3D velocity profile (http://www.cfd-online.com/Forums/fluent/31891-3d-velocity-profile.html)

S. Sarkar July 27, 2003 04:29

3D velocity profile
 
I have a laminar, viscous 3D flow in a duct (brick type geometry) with rectangular cross-section. I want to use velocity inlet and pressure outlet boundary conditions. There is a nice expression for fully-developed velocity profile (parabola) in 2D (written in terms of u_max). How is it written in 3D? Any help or reference will be highly appreciated. Thanks in anticipation. S.S.

Lola July 27, 2003 05:47

Re: 3D velocity profile
 
I don't think you know the profile to rectangulat inlet, do you ? You know it for a circular inlet.

Lola

Mirek Kabacinski July 27, 2003 09:36

Re: 3D velocity profile
 
Hi, I dealt with the same problem. Solution of this problem is very simple. Let Fluent do it itself. They are two ways: 1. You can construct long inflow section such long as your fluid needs to create stable rectangular velocity proflie (its long depends on velocity, if your fluid flows faster then your run-up section must be longer). At the velocity-inlet B.C. type your mean velocity. 2. You can construct long brick with the same B.C. and at the outlet (or before it-check it by display velocity contour where is the best profile, here you must previously create new plane in cross-section of this brick)write velocity profile. The next step is read this profile in your problem and set it in velocity-inlet B.C. changing it in drop-down list from constant to .... it depends on the name of profile you used). And the next steps you know, I think. Good luck! If You had any problem I can help You again. Mirek

S. Sarkar July 28, 2003 18:12

Re: 3D velocity profile
 
Hello! Thanks a lot for your suggestions. Your suggestion no. 1 would not work for me because I'm doing 3D simulation on my PC and if I add extra section to the inlet, that will require more mesh elements and I may easily run into memory problems. Your suggestion no. 2 was great! I tried it, and it appeared to work pretty well. I was reading from the manual that there were different options for writing a profile such as point, line and mesh. However I didn't get any option - when I wrote the profile it was automatically written as point profile. I suppose the profile was written with cell-centered value, and I observed that when I displayed the profile (after reading it back and hooking it to the inlet), it wasn't showing the right values (zero) at the walls. Was it a problem of node interpolations? Anyways, that was a minor difference and I'm quite happy with the overall agreement. Thank you again for your kind help. Best regards.


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