how to deal with the wall boundary of les?
 

Ask for help! In the les turbulent model, how to deal with the wall boundary? And if the y+ is needed , how to calculate it?

Re: how to deal with the wall boundary of les?
 

In the boundary layer, you must use DNS resolution, in other words, y+ < 1. (see any standard book on turbulence for y+ calculation)

Wall models are an alternative, and you might want to try them.

Re: how to deal with the wall boundary of les?
 

agg, can talk about the calculation of y+ in les ? The y+ fomulation need k, but how to get it in les??

Re: how to deal with the wall boundary of les?
 

y+ is just a non-dimensional distance based on friction velocity

y+ = y*utau/viscosity utau = (wall shear stress/density)^0.5

You can calculate wall shear stress from LES using velocity gradient at the wall and hence y+

Re: how to deal with the wall boundary of les?
 

agg, you mean the wall shear stress can get by using velocity gradient at the wall, so must use DNS resolution, in other words, y+ < 1??? But when the y+>30, the wall shear stress is diff to get?

Re: how to deal with the wall boundary of les?
 

When y+ is not resolved, you can use wall models.

An example would be to use:

1) u+ = y+ in the viscous sublayer (if y+ <= 10) 2) u+ = 2.5 ln(y+) + 5.5 (if 10 < y+ <= 300)

For (2), an iterative procesure is required, since wall stress is an unknown in both LHS and RHS.

Once u+ is known, you can back calculate u at that point.

Best information can be found in papers. You should be able to find papers with LES using wall models.

Re: how to deal with the wall boundary of les?
 

Visit here http://www.lstm.uni-erlangen.de/~breuer/ and see this

CFD - Code LESOCC (Large Eddy Simulation on Curvilinear Coordinates)

Numerical Method

Discretization

Subgrid Scale Model

=== Wall Boundary Conditions ===

Good Luck!

Halim

Re: how to deal with the wall boundary of les?
 

i am reading, thanks halim!

Re: how to deal with the wall boundary of les?
 

hi....halim

the Code LESOCC is shared?

where can get some code for learning?

Re: how to deal with the wall boundary of les?
 

(1) Ask to Dr. Breuer (E-mail: breuer_at_lstm.uni-erlangen.de )

(2) Sorry, I do not know. I know that if you buy this book, you can have a source code for LES. "Fluid Flow Phenomena : A Numerical Toolkit" by Paolo Orlandi, Kluwer Academic Publishers, 2000.

Halim