mixing fresh-saltwater
 

Hi, i'm really new to OpenFoam and i'm looking for a solver that can simulate the mixing between salt water and fresh water. In principle it's just one phase and i have to solve the transport equation for the solute (NaCl) that affects the density,there's any specific solver??. I look to interMIxingFoam putting phase2 fresh and phase3 salt water and setting the diffusion coeff between them. But i don't understand the physic behind this solver : that coeff of diffusion can be treat as molecular diffusion ? which is the transport equation that rule the process? ... and what about twoLiquidMixingFoam....thanks very much

Hi aronne,
i think twoLiquidMixingFoam is perfect for your issue.
Is a solver for mixing between two fluids (single phase) with different diffusion properties.
You will see that the transport equation will use the scalar alpha as ratio between the two different densities.
You can explore the solver here
applications/solvers/multiphase/twoLiquidMixingFoam/
Tommy

Hi Tommy Thank you,
i loked into the solver folder. Am i right saying that i can consider molecular diffusion between saltwater and freshwater as the Dab coefficients to set in the transportPropertiesDict?? then there's also a turbulence diffusion ( alphatab*turbulence->nut() ) that in my work i will not consider since my flow are laminar.

FROM fille
AlphaDiffusionEqn.H

{
fvScalarMatrix alpha1Eqn
(
fvm::ddt(alpha1)
- fvc::ddt(alpha1)
- fvm::laplacian
(
volScalarField("Dab", Dab + alphatab*turbulence->nut()),
alpha1
)
);

alpha1Eqn.solve();

alpha2 = 1.0 - alpha1;
rhoPhi += alpha1Eqn.flux()*(rho1 - rho2);
}

rho = alpha1*rho1 + alpha2*rho2;

This is the ./constant/transportProperties for twoLiquidMixingFoam
https://github.com/OpenFOAM/OpenFOAM...portProperties
You will see Dab [0 2 -1 0 0 0 0], or else [m^2/s]: yes, that's the molecular diffusivity.
About nut: yes, if you're in laminar you can also delete it.

thank you so much , it seem to work. Have a nice job!!

cool! I had to work a lot on that solver, if you need any help (principally via LES models) just ask.
have fun!

Dear Villo,

I use twoLiquidMixingFoam solver in OpenFOAM. In my setup, I have a single inlet and two outlets as shown in the attachment. The two fluids are expected to mix and exit through the outlets.
I am wondering what would be the boundary conditions for the alpha phase in this case.
I use zeroGradient or inletOutlet. Initially, it works fine since only single phase exists at the outlet boundary. However, when a mixed phase reaches the outlet boundary, I get some vortices (see attachment).
In the zero directory, I have three files only; p_rgh, U and alpha.phase1.
I would appreciate any assistance.
Thanks.