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-   -   Alpha in IDDES (https://www.cfd-online.com/Forums/openfoam/82723-alpha-iddes.html)

 tookey_1989 December 3, 2010 12:10

Alpha in IDDES

Hello,

The way alpha is calculated in IDDES seems slightly wrong. It should be -

alpha = 0.25 -dw/hmax

where hmax is a local cell maximum length e.g. max(dx,dy,dz). In the source however I think it is calculating the max cell length in the entire mesh and hence not using a local max. Currently its -

tmp<volScalarField> SpalartAllmarasIDDES::alpha() const { return max ( 0.25 - y_/dimensionedScalar("hMax", dimLength, max(cmptMax(delta()))), scalar(-5) ); }
Am I right in thinking this returns a mesh-wide maximum? what exactly does the cmptMax() do?

How can I change it to find the local max, or use the deltamax calculated in IDDESDelta.c ?

Thanks
James

 Anne Lincke July 3, 2012 05:44

Hey James,
Quote:
 Originally Posted by tookey_1989 (Post 285898) Hello, The way alpha is calculated in IDDES seems slightly wrong. It should be - alpha = 0.25 -dw/hmax where hmax is a local cell maximum length e.g. max(dx,dy,dz). In the source however I think it is calculating the max cell length in the entire mesh and hence not using a local max. Currently its - tmp SpalartAllmarasIDDES::alpha() const { return max ( 0.25 - y_/dimensionedScalar("hMax", dimLength, max(cmptMax(delta()))), scalar(-5) ); } Am I right in thinking this returns a mesh-wide maximum?
Yes, you are right. The implementation is wrong, as it returns a global and not a local maximum. It should be fixed in OF-2.1.1, see also
http://www.cfd-online.com/Forums/ope...tml#post368916

Quote:
 Originally Posted by tookey_1989 (Post 285898) How can I change it to find the local max, or use the deltamax calculated in IDDESDelta.c ?
See the newest version of OpenFOAM, currently OF-2.1.1

Regards
Anne

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