# LES: subgrid-scale mixing rate

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 March 24, 2014, 08:59 LES: subgrid-scale mixing rate #1 New Member   Alberto Cuoci Join Date: Mar 2014 Posts: 1 Rep Power: 0 Hello everybody, I need to calculate the subgrid-scale mixing rate TauSGS in a LES simulation, which is defined in the following way: TauSGS = 1 / sqrt ( 2 * Sij*Sij) where Sij is the strain rate tensor (in 1/s), i.e.: Sij = 0.5 * ( dvi/dxj + dvj/dxi) where dvi/dxi is the derivative of j-th component of velocity with respect to the i-th coordinate 1. Do you know how I can calculate it in OpenFOAM? 2. Do you also know how I can distinguish if I am performing a RANS or a LES simulation? In other words, is there any function in the turbulenceModel class returning if this is a RANS or a LES? Thank you very much in advance! Alberto

 March 24, 2014, 18:10 #2 Senior Member   Lieven Join Date: Dec 2011 Location: Mol, Belgium Posts: 295 Rep Power: 13 Hi Alberto, You can try something like: Code: ```volSymmTensorField S(dev(symm(gradU))); volScalarField magS(sqrt(2.0)*mag(S)); volScalarField tau("tau",pow(2*magS*magS,-0.5));``` I dind't try it but it might do the trick... Cheers, L

 Tags les model, strain rate, subgrid scale

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