CFD Online Discussion Forums - what's the sigma meaning in the Perturbu.C

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what's the sigma meaning in the Perturbu.C

I want to simulation LES with magnatic, but it need a perturbu utility,It had a error when i compiled it,because I had a variable "sigma" is conflict with the "sigma" in the Perturbu.C,look below ,anybody could tell me what's the sigma meaning in the Perturbu.C,my sigma represent electric conductivity,is it same ?

// streak streamwise velocity
U[celli][streamDir] +=
(utau * duplus/2.0) * (yplus/40.0)
* Foam::exp(-sigma * Foam::sqr(yplus) + 0.5)
* Foam::cos(betaPlus*zplus)
* deviation;

// streak spanwise perturbation
U[celli][spanDir] =
epsilon
* Foam::sin(alphaPlus*xplus)
* yplus
* Foam::exp(-sigma*Foam::sqr(yplus))
* deviation;

Quick answer: From post #14 at http://www.cfd-online.com/Forums/ope...tml#post494266

Quote:

Code:

// Perturbation properties

//wall normal circulation as a fraction of Ubar/utau

duplus 0.25;

//spanwise perturbation spacing in wall units

betaPlus 200;

//streamwise perturbation spacing in wall units

alphaPlus 500;

//transverse decay

sigma 0.00055;

//linear perturbation amplitude as a fraction of Ubar

epsilon 0.005;