# Ubar and Ubulk

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 July 4, 2007, 06:20 Hi to all Can u please tell #1 Member   hadi tartoussi Join Date: Mar 2009 Location: paris Posts: 48 Rep Power: 10 Hi to all Can u please tell me what is the difference betwwen Ubulk and Ubar (for a LES turbulent channel flow) and how to calculate it for a given Re-tau. Thanks in advance Hadi Luttappy likes this.

 July 4, 2007, 12:06 for the case of isothermal pla #2 Senior Member   Maka Mohu Join Date: Mar 2009 Posts: 305 Rep Power: 11 for the case of isothermal plane channel flow: In literature, Ubulk usually is a volume averaged velocity which is a single number while, Ubar is usually an averaged (more accurately, an integral of) velocity (in time (after reaching fully developed flow and in homogeneous directions (x, z))), so it is a function of wall normal coordinate (Y); one can obtain Ubulk from Ubar by: Ubulk=integral of (Ubar dy); where y is wall normal direction and Ubar is function of y; have a look at postChannel utility; If you are running your simulation by specifying Re_tau, then you are computing dimensionless variables. Try to derive the equations to be sure what are you doing. Have a nice day! Best regards, Maka. solefire, songwukong and Luttappy like this.

 July 5, 2007, 08:52 Thanks alot for ur explanation #3 Member   hadi tartoussi Join Date: Mar 2009 Location: paris Posts: 48 Rep Power: 10 Thanks alot for ur explanation. But i am confused about Ubar in transportproperties (channelOodles solver) is it the centerline velocity? or bulk velocity? Actually i ran postchannel for channel395 tutorial and i have the same problem as urs posted on Monday, December 11 2006: (PostChannel: collapsed field result inconsistancy) can u please tell me how did u solve this problem? Thanks in advance regards Hadi

 July 6, 2007, 07:44 Hi Hadi, Ubar is the bulk v #4 Senior Member   Maka Mohu Join Date: Mar 2009 Posts: 305 Rep Power: 11 Hi Hadi, Ubar is the bulk velocity. I posted the solution of the postChannel problem in the message that you referred to. Please recheck the message to read the solution. Best regards, Maka

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