[chris1980]

I fell some trouble to implement a scalar transport eqn with the following source term:

C1*[grad(Xi)]^2 - C2*epsilon/k * rho * Xi

C1,C2: constants
epsilon: turbulent dissipation
k: turbulent kinetic energy

Xi: scalar variable


How do I have to implement this FOAM?

[chris1980]

the main problem is the realistation of the squared gradient [grad(Xi)]^2

I have tried to do this like:

volScalarField gradXiVar2 = fvc::grad(XiVar) &
...
solve
(
...
- fvm::Sp(...,gradXiVar2)
)

but the following error occurs:

--> FOAM FATAL ERROR : incompatible fields for operation
[XiVar] - [(grad(XiVar)&grad(XiVar))]

How can I realise this squared gradient term?

[chris1980]

ups there is type

volScalarField gradXiVar2 = fvc::grad(XiVar) & fvc::grad(XiVar)

[hjasak]

You've just for the the wrong way around:

In fvm::Sp, first put the multiplier and then the field you're solving for. Also, you seem to be confused by the meaning of things a bit:

- first things first: C1*[grad(Xi)]^2

C1*magSqr(grad(Xi)). Done.

- C1*[grad(Xi)]^2 is always positive, which makes it a source. Putting it into Sp will just harm your matrix structure. Thus, just leave it as a plain old field in the source

- if you want to make C2*epsilon/k * rho * Xi, please tell me which variable you want to make it implicit in. In other words, what equation are you solving where this appears as the source term. I will assume you're solving for Xi: in this case, the Sp term would read:

fvc::Sp(C2*epsilon/k*rho, Xi)

Note that C2*epsilon/k*rho, is always positive and the minus in front of it makes this a sink term, so there's a point in making this an Sp. As you can see, the multiplier comes first and then the field (Xi) that you're solving for.

Enjoy,

Hrv

[chris1980]

thanks Hrv!

just to make sure I get you right:

I want to solve a Xi-eqn and the problem is to implement the following source terms

C1*[grad(XXi)]^2 - C2*Xi

the first term I already know from the XXi-Eqn so I think I can simply write
C1*magSqr(fvc::grad(XXi))

the second term is always a sink (as you already mentioned) so an implicit formulation will advance the diagonal dominance of my matrix so you write

fvc::Sp(C2*epsilon/k*rho, Xi)

but why not fvm::Sp(C2*epsilon/k*rho, Xi) ???


Am I on the right way?

[hjasak]

Sorry, my fault: it should (of course) be fvm::Sp(C2*epsilon/k*rho, Xi)

Hrv

[marhamat]

Hi everybody

When i add a source term (grad(Fi)) to momentum equation in icoFoam solver i get the below error
Where:
Gravity defined as Gravity [0 1 -2 0 0 0 0] 9.81
and:
volScalarField Fi = Gravity.value() * mesh.C().component(1) ;


fvVectorMatrix UEqn
(
fvm::ddt(U)
+ fvm::div(phi, U)
- fvm::laplacian(nu, U)
);

solve(UEqn == fvc::grad(Fi)-fvc::grad(p));

....
SOURCE_DIR=.
SOURCE=icoFoam.C ; g++ -m32 -Dlinux -DDP -Wall -W -Wno-unused-parameter -Wold-style-cast -O3 -DNoRepository -ftemplate-depth-30 -I/marhamat/OpenFOAM/OpenFOAM-1.3/src/finiteVolume/lnInclude -I/marhamat/OpenFOAM/OpenFOAM-1.3/src/OpenFOAM/lnInclude -IlnInclude -I. -fPIC -pthread -c $SOURCE -o Make/linuxGcc4DPOpt/icoFoam.o
icoFoam.C: In function 'int main(int, char**)':
icoFoam.C:66: error: 'Fi' was not declared in this scope
make: *** [Make/linuxGcc4DPOpt/icoFoam.o] Error 1

What is the matter?
Thanks alot
Marhamat

[alberto]

The definition of Fi is inside braces {}, so it's not accessible when it's used in the solve line.

Check where Fi is defined.

Regards,
A.

[morteza]

Hello everybody
After running the new icoFoam solver that changed by adding grad(Fi) as a source term , the vorticity magnitude increased with opposite of my expection .
I used inlet and outlet for inlet&outlet boundries and other boundries are symmetryplane
You can see the vorticitymag before and after of adding grad(Fi).I explaned Fi in my last message in this page.
:
:
:
Do you think i get correct result?
An How i can decrease the vorticity magnitude?

Have a nice weekend
Marhamat

[marhamat]

Hi guys
I send the above message with my friend.
So anything is right.
sorry for disturbing you

Marhamat

[marhamat]

Ideas are welcome.(-:
Thanks alot