# weird velocity profile

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November 8, 2012, 19:24
weird velocity profile
#1
New Member

Raef
Join Date: Nov 2011
Posts: 16
Rep Power: 7
hello I have been trying to do a CFD simulation on a venturi pipe using RNG k epsillon method, the solution converged but when I took a plane to check the velocity profile on it I found out that in the middle of the section plane the velocity is low and on the sides near the wall the velocity get high thn it come close to zero near on the wall.

I have attached an image for the simulation , I just want to know if this is normal or not .
flow rate is :387 kg/s. fluid is water. inlet diameter is 0.8m , diameter of the pipe after the constriction is 0.4m. the section plane was taken in the constricted area.
Please find attached 2 images showing the velocity profile and the geometry of my case.
Attached Images
 1.jpg (83.5 KB, 21 views) 2.jpg (79.1 KB, 22 views)

 November 8, 2012, 22:01 #2 New Member   Raef Join Date: Nov 2011 Posts: 16 Rep Power: 7 can anyone help please ?

 November 9, 2012, 00:10 #3 Super Moderator   Sijal Join Date: Mar 2009 Location: Islamabad Posts: 4,331 Blog Entries: 6 Rep Power: 45 This is not normal!!! What is the boundary condition on wall : slip or no slip?

November 9, 2012, 05:24
#4
New Member

Raef
Join Date: Nov 2011
Posts: 16
Rep Power: 7
No slip conditions, and I have another plan section that might help identify the problem please check it , it is attached below. Do you think it is a mesh problem ? I set the solution monitor to 1e-3 for k epsilon velocities and momentum.
Attached Images
 CFD.jpg (97.6 KB, 12 views)

 November 9, 2012, 05:39 #5 Super Moderator   Sijal Join Date: Mar 2009 Location: Islamabad Posts: 4,331 Blog Entries: 6 Rep Power: 45 reduce convergence criteria to 1e-5 and run for longer time and then see... Would you describe your problem in detail?

 November 9, 2012, 06:42 #6 New Member   Raef Join Date: Nov 2011 Posts: 16 Rep Power: 7 it is a venturi pipe with water flowing at 387 kg/s thats all, it is very simple and straight forward althoug I was surprised of the velocity profile that I have got , I knew it is unusual . I am trying to work on the mesh at the moment and see if it changes something, it looks like I have got a separation of flow in this case. it is weird !

 November 9, 2012, 07:09 #7 Super Moderator   Sijal Join Date: Mar 2009 Location: Islamabad Posts: 4,331 Blog Entries: 6 Rep Power: 45 can you share the mesh and case file so that I can check it by running it on my computer.

 November 9, 2012, 07:14 #8 New Member   Raef Join Date: Nov 2011 Posts: 16 Rep Power: 7 ok that would be great can you give me your email so that I send it to you please.

 November 9, 2012, 07:15 #9 Super Moderator   Sijal Join Date: Mar 2009 Location: Islamabad Posts: 4,331 Blog Entries: 6 Rep Power: 45 just look at the left and you will find the email id

 November 9, 2012, 07:30 #10 New Member   Raef Join Date: Nov 2011 Posts: 16 Rep Power: 7 Hello, the files are big and they cannot be uploaded to gmail, so I will upload them on my website and send u the link with the password to your E-mail, thank you for your help

 November 9, 2012, 07:32 #11 Super Moderator   Sijal Join Date: Mar 2009 Location: Islamabad Posts: 4,331 Blog Entries: 6 Rep Power: 45 you can upload it to dropbox.

 November 9, 2012, 07:33 #12 New Member   Raef Join Date: Nov 2011 Posts: 16 Rep Power: 7 I am sorry I am already uploading it to my website, it is the same thing, I dont have an account with dropbox. it is very easy to download it from the webste, just right click on the file name and download it , i have uplaoded 2 files with .rar extention.

 November 9, 2012, 07:54 #13 New Member   Raef Join Date: Nov 2011 Posts: 16 Rep Power: 7 Hello, I sent you the link , thank you very muich

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