# Turbulence models and wall boundary conditions

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 August 1, 2008, 07:15 G ~= tauw*(dU/dy)p, G != tauw* #21 Senior Member   Eugene de Villiers Join Date: Mar 2009 Posts: 725 Rep Power: 14 G ~= tauw*(dU/dy)p, G != tauw*Up/yp, i.e. (dU/dy)p != Up/yp Log-law U = utau/kappa*ln(y*utau/nu * E); or dU/dy = utau /(kappa*y); utau = Cmu25*sqrt(k); Clear?

 August 2, 2008, 02:50 Thanks Eugene, this is clear t #22 Member     Stefan Radl Join Date: Mar 2009 Location: Graz, Austria Posts: 82 Rep Power: 11 Thanks Eugene, this is clear to me. BUT: My literature (lecture notes from a AVL guy) tells me G=tau_wall*UP/yP. Furthermore, something like G=tauw*UP/yP-rho*Cmu75*kP^1.5*u^+/yP can be found in Versteeg and Malalasekera (Computational Fluid Dynamics, 1995), which was a little confusing to me. However, OF'S approach sounds more physical. By the way: can you recommend some recent literature for this kind of aspects (except your PhD thesis)? cheers Stefan

 August 4, 2008, 06:45 This one: G=tauw*UP/yP-rho* #23 Senior Member   Eugene de Villiers Join Date: Mar 2009 Posts: 725 Rep Power: 14 This one: G=tauw*UP/yP-rho*Cmu75*kP^1.5*u^+/yP : utau^3 = Cmu75*kP^1.5 utau^2 = tauw/rho and u+ = UP/utau thus G=tauw*UP/yp - tauw*UP/yP Doesn't sound very correct to me unless some of my assumptions were wrong. But don't take my word for it, you can work it out yourself. The definition of G is: G = 1/yN * int(tau_turb * dU/dy.dy)[0-yN] Normally people make various assumptions to simplify things, like the laminar region is negligible, tau_turb is constant and equal to tauw , etc. For recent literature, do a google on "UMIST wall functions".

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