Hello, I am running a LES t
 

Hello,

I am running a LES to simulate the dispersion of
a passive contamimant.

I have tried linearLimited01 schemes for the scalar transport
equation but I still have negative values.

Could you please inform me about the best
schemes available in OpenFoam to chose to ensure a positive scalar?


Thanks You

Anne

Use Gamma01 with the coefficie
 

Use Gamma01 with the coefficient of 0.5 or 1. You also need to limit the Laplace scheme for that scalar, e.g.

laplacian(DkEff,k) Gauss linear limited 1;

On bad meshes you may need to use a lower coefficient, say 0.5

That should do it,

Hrv

Forgot to say: temporal discre
 

Forgot to say: temporal discretisation may also give you unboundedness. A good way forward is Euler implicit (first order); if you really need second order you can try my new boundedBackward scheme.

Hrv

Dear Hrvoje, Thank you,
 

Dear Hrvoje,

Thank you,

I will test your suggestions.

Anne

I want to try different ddt-sc
 

I want to try different ddt-schemes.
In order to see the choices I wrote "x":
------------------------------------------
Creating field DpDt
--> FOAM FATAL IO ERROR : unknown ddt scheme x
Valid ddt schemes are :
6
(
CoEuler
boundedBackward
CrankNicholson
steadyState
Euler
backward
)
file: /home/workdisc/OpenFOAM/pen-1.3/run/boundp3/system/fvSchemes::default at line 27.
From function ddtScheme<type>::New(const fvMesh&, Istream&)
in file /home/dm2/henry/OpenFOAM/OpenFOAM-1.3/src/finiteVolume/lnInclude/ddtScheme.C at line 80.
FOAM exiting
------------------------------------------

When I try boundedBackward I get:
------------------------------------------
Creating field DpDt
Starting time loop
Time = 2e-06
Mean and max Courant Numbers = 0 0
diagonal: Solving for rho, Initial residual = 0, Final residual = 0, No Iterations 0
--> FOAM FATAL IO ERROR : unknown ddt scheme boundedBackward
Valid ddt schemes are :
5
(
CoEuler
CrankNicholson
steadyState
Euler
backward
)
file: /home/workdisc/OpenFOAM/pen-1.3/run/boundp3/system/fvSchemes::default at line 27.
From function ddtScheme<type>::New(const fvMesh&, Istream&)
in file /home/dm2/henry/OpenFOAM/OpenFOAM-1.3/src/finiteVolume/lnInclude/ddtScheme.C at line 80.
FOAM exiting
------------------------------------------

Why is boundedBackward no longer on the list?

Easy: a bounded backward schem
 

Easy: a bounded backward scheme I wrote is there for scalars only: you cannot define what "bounded" means in terms of a vector or a tensor. Therefore, I cannot define a bounded second-order scheme for a vector.

In order to do this well, you will need to specify a scheme on a per-ddt-term basis. Set default to none and the code will ask you for a scheme one ddt term at a time.

Hrv