[Andrea_85]

Hi all,
i have a question regarding the interFoam solver. Why the alpha equation is solved explicit? From alphaEqn.H we have:

 for (int aCorr=0; aCorr<nAlphaCorr; aCorr++)
00012     {
00013         surfaceScalarField phiAlpha =
00014             fvc::flux
00015             (
00016                 phi,
00017                 alpha1,
00018                 alphaScheme
00019             )
00020           + fvc::flux
00021             (
00022                 -fvc::flux(-phir, scalar(1) - alpha1, alpharScheme),
00023                 alpha1,
00024                 alpharScheme
00025             );
00026 
00027         MULES::explicitSolve(alpha1, phi, phiAlpha, 1, 0);
00028 
00029         rhoPhi = phiAlpha*(rho1 - rho2) + phi*rho2;
00030     }

I'm running simulation of water and air in a microchannel (200micron long and 50 micron wide, 2 dimensional): the time step is very small (not higher than 1e-7 s) and the simulation takes a very long time. I also found very high velocities (spurious) at the interface. I'm able to reduce these velocities by reducing the Courant number but the simulation time increase more (i'm using adjustable time step). My question is: using an implcit MULES to solve the alpha equation (for expample is used in interPhaseChangeFoam) would not be better? Normally using an implicit solver allows you to have fewer restrictions on the time step, so why in interFoam an explicit is used?

From my experience, simulations at the scale of millimeters do not give this kind of problem and the time step is well described by the CourantNumer's formula and i dont understand why decreasing the dimension should mean decrease the time step.

Thanks

andrea