y+ and airpak

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 November 10, 2005, 12:47 y+ and airpak #1 Drauss Guest   Posts: n/a iam using a commercial code which is though based on Fluent, doesnt have the post-processing feature where we can compute y+. based on littreture work for indoor ventilation it is recommended to put the first grid at the distance of 10 mm from the wall. However, iam curious as what is the y+ for that location. therefore i need to compute y+ manually to see whats going on; by checking the net i found the following formulae: y+ = sqrt(t/density)*(first grid distance/dynamic viscosity) i used k-e model and please can someone clarify the following point. What does t represents in the formulae; how come y+ doesnt take into account the velocity?? many thanks for your time

 November 11, 2005, 02:21 Re: y+ and airpak #2 D.Pavitran Guest   Posts: n/a Hi, t = wall shear stress, sqrt of wall shear stress over density = frictional velocity.

 November 11, 2005, 12:01 Re: y+ and airpak #3 Drauss Guest   Posts: n/a thanks any idea how can i determine the wall shear stress; i ofcourse do have the viscosity (mui) but del-y/del-x; i do not have is there an alternative to compute the y+

 November 11, 2005, 13:14 Re: y+ and airpak #4 Jonas Larsson Guest   Posts: n/a You can estimate y+ with one of the tools here: http://www.cfd-online.com/Links/tools.html#yplus

 November 11, 2005, 13:45 Re: y+ and airpak #5 Drauss Guest   Posts: n/a thank you for the link. my problem is a 8.4-by-7.2 meter room; can i quantify the length scale as 8.4; iam not sure i can use the diffuser's hydraulic diameter as a length scale for this problem also, i want to ask how can i estimate the time-step for an unsteady simulation, using the referance length scale and referance velocity scale?? many thanks

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