# I have a problem about the turbulence flow!

 User Name Remember Me Password
 Register Blogs Members List Search Today's Posts Mark Forums Read

 June 26, 2003, 05:51 I have a problem about the turbulence flow! #1 yuchang Guest   Posts: n/a Hello! ALL This is my first time to be here and to ask some question! As we know, the velocity profile of turbulence in the circular tube is about obeying 1/7 power law. I use this knowledge to practice the turbulence model, but I cannot get the value like the profile I said above. What happened, If anybody check the turbulence model in Fluent and get the same answer as the 1/7 power law! Thx for your help! Best regards.

 June 26, 2003, 12:12 Re: I have a problem about the turbulence flow! #2 Alex Munoz Guest   Posts: n/a Hi The power low 1/n apply to a especific Reynolds number therefore, you must to check your Reynolds number before choosing the value of n I sugguest that you read the document of Zagarola and also this web side to compare your simmulation with Zagarola's experiments http://www.princeton.edu/~gasdyn/Superpipe_data Best regards Alex Munoz

 June 26, 2003, 20:38 Re: I have a problem about the turbulence flow! #3 yuchang Guest   Posts: n/a Thank you for your advice! From the Book written by Prof. Bird " Transport Phenomena", he noted that the 1/7 power law is applied in the range of Reynold no. between 10000 and 100000. and I set the condition in the range. And do you have another comments? thx for your help

 June 26, 2003, 21:14 Re: I have a problem about the turbulence flow! #4 Alex Munoz Guest   Posts: n/a Hi Sometimes authors write in a generic scenario !! If you read the Boundary Layer Theory by Schlichting Hermamm, you will find that at at different Reynolds Numbers you have a different 1/n power number Re n 4e03 6.0 2.3E04 6.6 1.1E05 7.0 Now you can see why some writers use n=7.0, however this value only applies for Re=1.1E05. Now If you cannot get the profile that you are expecting could be because: 1) Boundary conditions are poor defined 2) Your are using Tetrahedral mesh 3) Your are using first order discretization of the momentum equations 4) the turbulence model should not be used for this type or case 5) the number of cells near to the wall are not enough to describe the boundary layer. Therefore, I sugguest that you read and read, especially some cases already posted on this web. Best Regards Alex Munoz

 June 26, 2003, 21:21 Re: I have a problem about the turbulence flow! #5 yuchang Guest   Posts: n/a thx your for your advice again! I just want to know if Fluent can predict more correct values in turbulent case. So I choose the simplest case to try it! About what the reasons you suggest me, I think I all consider it! Maybe I should read more. Thank you after all!

 June 27, 2003, 00:33 Re: I have a problem about the turbulence flow! #6 Alex Munoz Guest   Posts: n/a Hi I can ensure you, because I have done this case, that fluent is able to project a parabolic velocity profile at the inlet of a pipe up to several meter down stream with a neglectable error!! Regards Alex Munoz

 June 27, 2003, 00:50 Re: I have a problem about the turbulence flow! #7 yuchang Guest   Posts: n/a Excuse me, what turbulent model do you use in that case? And how long is the entrance length if I want to get a fully-developed profile? Because I try it using the ratio of L/D over 100 times and can get the approximate value. Maybe something wrong in my operation. Thank you again! see u

 Thread Tools Display Modes Linear Mode

 Posting Rules You may not post new threads You may not post replies You may not post attachments You may not edit your posts BB code is On Smilies are On [IMG] code is On HTML code is OffTrackbacks are On Pingbacks are On Refbacks are On Forum Rules

 Similar Threads Thread Thread Starter Forum Replies Last Post fofo FLUENT 0 November 15, 2009 04:49 gRomK13 Main CFD Forum 1 July 10, 2009 03:11 Tony FLUENT 3 December 4, 2008 10:29 diaw Main CFD Forum 104 February 16, 2006 06:44 jehanzeb FLUENT 5 August 3, 2004 08:04

All times are GMT -4. The time now is 11:32.

 Contact Us - CFD Online - Top