Understanding LESDeltas

francesco_capuano · December 6, 2011, 11:28

Hi everyone,
I am trying to understand deeply the implementation of LES into OpenFoam, and I have a problem with the vanDriestDelta and the PrandtlDelta codes: I cannot understant the Cdelta_ coefficient in the following formulas for calculating delta:

(kappa_/Cdelta_)*wallDist(mesh_).y()
(kappa_/Cdelta_)*((scalar(1) + SMALL) - exp(-y/ystar/Aplus_))*y

Except for Cdelta_, these are the well-known Prandtl's mixing length and van Driest's damping function formulas, respectively. The default value for Cdelta_ is set to be 0.158: do any of you know where this value come from?

Thanks in advance,
Francesco

caoyinyue · February 1, 2014, 01:06

Dear Francesco,
These days, I am also confused about the Cdelta_ when I want to use the vanDriest damping function for LES. Have you found any information about it?
Another problem is, usually we use the vanDriest function to multiply the cube root of volume for LES near the wall. But herein, Openfoam use the damping function multiply the mixing length (kappa*y), which is often utilized in RANS models.
Could you give some any hint?
Thanks very much.
Yong

HakikiCanakkaleli · July 26, 2014, 14:11

Hi,

== 1 ==
Please look at p. 260 of his PhD thesis:
http://powerlab.fsb.hr/ped/kturbo/Op...ersPhD2006.pdf

December 6, 2011, 11:28	Understanding LESDeltas	#1
francesco_capuano Member Francesco Capuano Join Date: May 2010 Posts: 81 Rep Power: 16	Hi everyone, I am trying to understand deeply the implementation of LES into OpenFoam, and I have a problem with the vanDriestDelta and the PrandtlDelta codes: I cannot understant the Cdelta_ coefficient in the following formulas for calculating delta: (kappa_/Cdelta_)wallDist(mesh_).y() (kappa_/Cdelta_)((scalar(1) + SMALL) - exp(-y/ystar/Aplus_))*y Except for Cdelta_, these are the well-known Prandtl's mixing length and van Driest's damping function formulas, respectively. The default value for Cdelta_ is set to be 0.158: do any of you know where this value come from? Thanks in advance, Francesco caoyinyue and the_ichthyologist like this.

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February 1, 2014, 01:06		#2
caoyinyue New Member caoyong Join Date: Nov 2013 Location: Tokyo, Japan Posts: 3 Rep Power: 13	Dear Francesco, These days, I am also confused about the Cdelta_ when I want to use the vanDriest damping function for LES. Have you found any information about it? Another problem is, usually we use the vanDriest function to multiply the cube root of volume for LES near the wall. But herein, Openfoam use the damping function multiply the mixing length (kappa*y), which is often utilized in RANS models. Could you give some any hint? Thanks very much. Yong

July 26, 2014, 14:11		#3
HakikiCanakkaleli Senior Member Canakkale Dardanelspor Join Date: Aug 2012 Posts: 135 Rep Power: 14	Hi, == 1 == Please look at p. 260 of his PhD thesis: http://powerlab.fsb.hr/ped/kturbo/Op...ersPhD2006.pdf