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Old   August 1, 2008, 07:15
Default G ~= tauw*(dU/dy)p, G != tauw*
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Eugene de Villiers
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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?
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Old   August 2, 2008, 02:50
Default Thanks Eugene, this is clear t
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Stefan Radl
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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
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Old   August 4, 2008, 06:45
Default This one: G=tauw*UP/yP-rho*
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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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