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-   -   New blending function in kOmegaSST (http://www.cfd-online.com/Forums/openfoam-programming-development/115783-new-blending-function-komegasst.html)

Tarak April 6, 2013 14:44

New blending function in kOmegaSST
 
Hii,

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 );
00096
00097 return 1 - tanh(pow4(arg3));
00098 }
00099
00100
00101 tmp<volScalarField> kOmegaSST::F23() const
00102 {
00103 tmp<volScalarField> f23(F2());
00104
00105 if (F3_)
00106 {
00107 f23() *= F3();
00108 }
00109
00110 return f23;
00111 }

Can someone please explain me the reason for this change?

fumiya April 8, 2013 06:21

Hi Tarak,

I found the answers in the following sites:
  • In the header of kOmegaSST.H file
    https://github.com/OpenFOAM/OpenFOAM...ST/kOmegaSST.H

    Quote:

    Description
    Implementation of the k-omega-SST turbulence model for incompressible
    flows.

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

    with the addition of the optional F3 term for rough walls from
    \verbatim
    Hellsten, A.
    "Some Improvements in Menterís k-omega-SST turbulence model"
    29th AIAA Fluid Dynamics Conference,
    AIAA-98-2554,
    June 1998.
    \endverbatim

  • http://www.openfoam.org/mantisbt/view.php?id=693
    Quote:

    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,
Fumiya

Tarak April 8, 2013 12:47

Thanks a lot, Fumiya.


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