- **OpenFOAM**
(*http://www.cfd-online.com/Forums/openfoam/*)

- - **mykEpsilon - How to set a min/max constraint for a term with units**
(*http://www.cfd-online.com/Forums/openfoam/80942-mykepsilon-how-set-min-max-constraint-term-units.html*)

mykEpsilon - How to set a min/max constraint for a term with unitsHello all,
I have implemented a k-epsilon turbulence model and named my directory "mykEpsilon". In mykEpsilon.C, I have a term called "sstar_" that has units of (1/sec^2) that is defined as a volScalarField in mykEpsilon.H. Now, in mykEpsilon.C, I would like to fix a "min" constraint on this term. The code compiles but I get an error when running (regarding unmatched dimensions). These are the lines that I use in mykEpsilon.C to initialize: gradU_(fvc::grad(U)), ss_(0.5*(gradU_ + gradU_.T())), sstar_(sqrt(max(ss_ && ss_.T(),1.0e-10))), The problem is with the term "sstar_". "ss_" is defined as a volTensorField. "ss_ && ss_.T()" should give a volScalarField with units of (1/sec^2). "sstar_" is defined as a volScalarField. So the error is coming up because the code is attempting to compare a term that has units of (1/sec^2) to a number (1e-10) that is unitless. Does anyone know how to fix this? Thank you! FYI, my code was running well before I attempted to add the "min" constraint. |

Hi elektra79,
my simplest solution would be to initialize a field in createFields.H which has the desired dimension and a constant value. It would look something like this volScalarField yourConstantValueScalarField ( IOobject ( "yourConstantValueScalarField", runTime.timeName(), mesh, IOobject::NO_READ, IOobject::NO_WRITE ), mesh, dimensionedScalar("zero",dimensionSet (0, 0, -2, 0, 0, 0, 0), 1e-10) ); It might not be the most elegant way to solve your problem but it does the trick. Ciao, Sabin |

Hi Sabin. Thank you for your reply.
Here is what I added to "createFields.H" which is located in the "applications/solvers/incompressible/pisoFoam" directory: volScalarField s_lim ( IOobject ( "s_lim", runTime.timeName(), mesh, IOobject::NO_READ, IOobject::NO_WRITE ), mesh, dimensionedScalar("one-e-neg-ten", dimensionSet(0, 0, -2, 0, 0, 0, 0),1.0e-10) ); My questions now are: (1) How would this feed back to the directory that holds my turbulence model? How would I denote a "pointer" to this variable? (2) How would I use this in "mykEpsilon.C"? I tried the following in "mykEpsilon.C" and got errors when trying to compile: gradU_(fvc::grad(U)), ss_(0.5*(gradU_ + gradU_.T())), sstar_(sqrt(max(ss_ && ss_.T(),"one-e-neg-ten"))), Thank you! |

It is now working. I am able to fix a min/max constraint for the term "sstar_".
In "mykEpsilon.C", I did the following for initializing: gradU_(fvc::grad(U)), ss_(0.5*(gradU_ + gradU_.T())), s_lim ( IOobject ( "s_lim", runTime_.timeName(), mesh_, IOobject::NO_READ, IOobject::NO_WRITE ), mesh_, dimensionedScalar("s_lim",dimensionSet(0, 0, -2, 0, 0, 0, 0),1.0e-10) ) , sstar_(pow(max(ss_ && ss_.T(),s_lim),0.5)), In "mykEpsilon.H", I added: volTensorField gradU_; volTensorField ss_; volScalarField s_lim; volScalarField sstar_; Thank you for the tips! |

All times are GMT -4. The time now is 09:19. |