Problems with cavitatingFoam
 

Hi guys! I am using cavitatingFoam to run a 2D simulation of cavitation inside a Venturi duct. The case i am reffering to is in the following link, in particular the Venturi with the angles of 8° and 18° before and after the throat: https://hal.archives-ouvertes.fr/hal-00912579/document
I used the files of the tutorial of cavitatingFoam (RAS-throttle) to set up my case.
I'm imposing velocity (7 m/s) and density (998.2 kg/m3) at the inlet, and static pressure at the outlet (72000 Pa). I am also using the k-omegaSST turbulence model.
At first i didn't change anything in the tutorial files but the boundary initial conditions, the fluid properties and the deltaT (10^-5), but the simulation was very unstable and it gave me this kind of error while iterating:

eltaT = 8.2622e-19
--> FOAM Warning :
From function Time::operator++()
in file db/Time/Time.C at line 1055
Increased the timePrecision from 6 to 7 to distinguish between timeNames at time 1.6997

Anyway I could see in Paraview that the simulation wasn't completely wrong because there was cavitation right after the trhoat in the separation zone where it is supposed to be, which then spread further. The problem is that right from the first iterations there was a thin irregoular layer near the wall far from the separation area,which sometimes becomes bigger during the simulation, where cavitation occurs as well, and i don't understand why!
Moreover the behaviour of the pressure field inside was very strange and it doesn't seem to have sense. I looked at the residuals of pressure during the simulation and the Initial Residuals are much higher than the ones of the other variables.
Than i changend the solver for "p" in the fvSolution file from GAMG to PCG because I read a post written by somebody having the same "FOAM warning" previously mentioned who solved it this way.
p
{
solver PCG;
preconditioner DIC;
tolerance 1e-06;
relTol 1e-05;
}

pFinal
{
$p;
tolerance 1e-08;
relTol 0;
}
Now the simulation goes better, without any warnings and really fast, but I see the same problems in the pressure field and initial residuals, and those cavitating zones close to the walls and far from the throat again.
Does anybody have any advice for me?