openFoam notes

http://www.cfd-online.com/Forums/openfoam/76246-explanation-bounding-k-bounding-epsilon.html

// source in k or epsilon equations have this:
rho_*epsilon_/k_

// mut calculation has this:
rho_*Cmu_*sqr(k_)/epsilon_

from
src/finiteVolume/cfdTools/general/bound/bound.C

Dividing by zero is avoided by bounding the values of k and epsilon.

Gauss linear for all convection terms is accurate.
Change to limitedLinear(V) 1; may help remove negative k values.

Upwind differencing gives bounded results but numerical diffusion.
Gauss linear is a second order central-difference scheme and does not assure boundedness.

limitedLinear is a blend of upwind and central difference. No: It is a limited CDS.

Consider refining the mesh in the problem region.

Other options: limitedLinear; linearUpwind; QUICK

People have had problems with backward facing steps. That is what I have.

Central differencing shows oscillation for idrama. limitedLinear(V) 1
removes it. Limiters switch between UD and CD.

*Check the mesh with, `checkMesh' to find skewed / non-orthogonal cells*
*Refine the mesh in problem regions*

*my note:  i also found cells with small determinants caused real problems in the boundary
layer.  These **really** should be avoided.  They made my simulations unstable but not immediately:
sometimes after many iterations*

Suggestions: Gradients use cellLimited Gauss linear 1;
divergence: Gauss linearUpwind cellLimited Gauss linear 1;
use linearUpwindV for div(phi,U) and other vector fields, with cellMDLimited.
Limit lapacians and surface normal gradients.

k-epsilon standard: zerogradient on inlet outlet, pressure zero.

fvSchemes requiring fixing:---------------------------

ddtSchemes{default steadyState;}

gradSchemes{default cellLimited Gauss linear 1;
grad(p) cellLimited Gauss linear 1; grad(U) cellLimited Gauss linear 1;}

divSchemes{default none;
div(phi,U) Gauss linearUpwindV cellMDLimited Gauss linear 1;
div(phi,k) Gauss linearUpwind cellLimited Gauss linear 1;
div(phi,epsilon) Gauss linearUpwind cellLimited Gauss linear 1;
div((nuEff*dev(grad(U).T()))) Gauss linearUpwind cellLimited Gauss linear 1;//Gauss linear;}

laplacianSchemes{default none; laplacian(nuEff,U) Gauss linear corrected;
laplacian((1|A(U)),p) Gauss linear corrected;
laplacian(DkEff,k) Gauss linear corrected;
laplacian(DepsilonEff,epsilon) Gauss linear corrected;}

interpolationSchemes{default linear;interpolate(U) linear;}

snGradSchemes{default corrected;}

fluxRequired{default no;p ;}