Waves in simple channel
 

Hello, forum!
I'm starting to learn the OpenFOAM and have a newbie question.
I would like to simulate the flow in very simple geometry:
a 2-phase parallelepiped with air-water interface. Without walls and bodies.
The OF version 1.5, the solver - interFoam. maxCo=0.3

The problem is as follows: at leading edge of free surface (at inlet)
raises the high value of velocity, which lead to raising of waves.
See attached pictures. Please advise how to avoid this problem.

Boundary conditions:

gamma:
in_air uniform 0;
in_water uniform 1;
out_water zeroGradient;
out_air zeroGradient;
top slip;
bottom slip;
side slip;

pd:
in_air zeroGradient;
in_water zeroGradient;
out_water zeroGradient;
out_air zeroGradient;
top slip;
bottom slip;
side slip;

U:
in_air uniform (1 0 0);
in_water uniform (1 0 0);
out_water zeroGradient;
out_air zeroGradient;
top slip;
bottom slip;
side slip;

================================================
fvSolvers:
solvers
{
pcorr PCG
{
preconditioner DIC;
tolerance 1e-10;
relTol 0;
};
pd PCG
{
preconditioner DIC;
tolerance 1e-7;
relTol 0.05;
};
pdFinal PCG
{
preconditioner DIC;
tolerance 1e-7;
relTol 0;
};
k PBiCG
{
preconditioner DILU;
tolerance 1e-05;
relTol 0.1;
};
omega PBiCG
{
preconditioner DILU;
tolerance 1e-05;
relTol 0.1;
};
U PBiCG
{
preconditioner DILU;
tolerance 1e-06;
relTol 0;
};
}

PISO
{
momentumPredictor no;
nCorrectors 3;
nNonOrthogonalCorrectors 0;
nGammaCorr 1;
nGammaSubCycles 2;
cGamma 1;

pdRefCell 1;
pRefCell 1;

pRefValue 1;
pdRefValue 0;
}
===============================================
fvSchemes:
ddtSchemes
{
default Euler;
}

gradSchemes
{
default Gauss linear;
grad(U) Gauss linear;
grad(gamma) Gauss linear;
}

divSchemes
{
div(rho*phi,U) Gauss limitedLinearV 1;
div(phi,gamma) Gauss vanLeer;
div(phirb,gamma) Gauss interfaceCompression;
div(phi,omega) Gauss upwind;
div(phi,k) Gauss upwind;
}

laplacianSchemes
{
default Gauss linear corrected;
}

interpolationSchemes
{
default linear;
}

snGradSchemes
{
default corrected;
}

fluxRequired
{
default no;
pd;
pcorr;
gamma;
}

Thanks in advance
Andrey