Turbulence models and wall boundary conditions

eugene · August 1, 2008, 08:15

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?

sradl · August 2, 2008, 03:50

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

eugene · August 4, 2008, 07:45

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".

August 2, 2008, 03:50	Thanks Eugene, this is clear t	#22
sradl Member Stefan Radl Join Date: Mar 2009 Location: Graz, Austria Posts: 82 Rep Power: 18	Thanks Eugene, this is clear to me. BUT: My literature (lecture notes from a AVL guy) tells me G=tau_wallUP/yP. Furthermore, something like G=tauwUP/yP-rhoCmu75kP^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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August 1, 2008, 08:15	G ~= tauw(dU/dy)p, G != tauw	#21
eugene Senior Member Eugene de Villiers Join Date: Mar 2009 Posts: 725 Rep Power: 21	G ~= tauw(dU/dy)p, G != tauwUp/yp, i.e. (dU/dy)p != Up/yp Log-law U = utau/kappaln(yutau/nu * E); or dU/dy = utau /(kappay); utau = Cmu25sqrt(k); Clear?

August 4, 2008, 07:45	This one: G=tauwUP/yP-rho	#23
eugene Senior Member Eugene de Villiers Join Date: Mar 2009 Posts: 725 Rep Power: 21	This one: G=tauwUP/yP-rhoCmu75kP^1.5u^+/yP : utau^3 = Cmu75kP^1.5 utau^2 = tauw/rho and u+ = UP/utau thus G=tauwUP/yp - tauwUP/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".