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New blending function in kOmegaSST

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Old   April 6, 2013, 14:44
Default New blending function in kOmegaSST
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The kOmegaSST model implemented in the latest version of OF contains a modified expression for nu_t with a changed blending function F23(),

00287 nut_ =
00288 (
00289 a1_*k_
00290 / max
00291 (
00292 a1_*omega_,
00293 b1_*F23()*sqrt(2.0)*mag(symm(fvc::grad(U_)))
00294 )
00295 );

where F23() is obtained from

00089 tmp<volScalarField> kOmegaSST::F3() const
00090 {
00091 tmp<volScalarField> arg3 = min
00092 (
00093 150*nu()/(omega_*sqr(y_)),
00094 scalar(10)
00095 );
00097 return 1 - tanh(pow4(arg3));
00098 }
00101 tmp<volScalarField> kOmegaSST::F23() const
00102 {
00103 tmp<volScalarField> f23(F2());
00105 if (F3_)
00106 {
00107 f23() *= F3();
00108 }
00110 return f23;
00111 }

Can someone please explain me the reason for this change?
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Old   April 8, 2013, 06:21
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Fumiya Nozaki
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Hi Tarak,

I found the answers in the following sites:
  • In the header of kOmegaSST.H file

    Implementation of the k-omega-SST turbulence model for incompressible

    Turbulence model described in:
    Menter, F., Esch, T.,
    "Elements of Industrial Heat Transfer Prediction",
    16th Brazilian Congress of Mechanical Engineering (COBEM),
    Nov. 2001.

    with the addition of the optional F3 term for rough walls from
    Hellsten, A.
    "Some Improvements in Menterís k-omega-SST turbulence model"
    29th AIAA Fluid Dynamics Conference,
    June 1998.

    The addition of the F3 term will change the results but it is recommended for some conditions, particularly with rough wall-functions. However, if the previous behaviour is prefered for some cases/conditions we could make the F3 term optional.
Hope this helps,
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Old   April 8, 2013, 12:47
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Thanks a lot, Fumiya.
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