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Old   December 3, 2010, 12:10
Default Alpha in IDDES
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James
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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
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Old   July 3, 2012, 05:44
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Anne Gerdes
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Hey James,
Quote:
Originally Posted by tookey_1989 View Post
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?
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
Anyone using IDDES

Quote:
Originally Posted by tookey_1989 View Post
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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