[nuovodna]

Hi, i have a standing wave case (box 1x1x1), velocity max value : 0.04, nu_water/nu_air = 10, Re=1060. I have to different mesh.
1) Structured mesh: generated by blockMesh 100x100x1
The cinetic energy plot is not like what i would but it's similar
http://dl.dropbox.com/u/3617688/Structured.png

2) Unstructured Mesh: made with gmsh
CheckMesh output:

Create polyMesh for time = 0

Time = 0

Mesh stats
    points:           10296
    internal points:  0
    faces:            35237
    internal faces:   14913
    cells:            10030
    boundary patches: 5
    point zones:      0
    face zones:       0
    cell zones:       1

Overall number of cells of each type:
    hexahedra:     0
    prisms:        10030
    wedges:        0
    pyramids:      0
    tet wedges:    0
    tetrahedra:    0
    polyhedra:     0

Checking topology...
    Boundary definition OK.
    Point usage OK.
    Upper triangular ordering OK.
    Face vertices OK.
    Number of regions: 1 (OK).

Checking patch topology for multiply connected surfaces ...
    Patch               Faces    Points   Surface topology                  
    patch0              66       134      ok (non-closed singly connected)  
    patch1              66       134      ok (non-closed singly connected)  
    patch2              66       134      ok (non-closed singly connected)  
    patch3              66       134      ok (non-closed singly connected)  
    defaultFaces        20060    10296    ok (non-closed singly connected)  

Checking geometry...
    Overall domain bounding box (0 -0.5 0) (1 0.5 1)
    Mesh (non-empty, non-wedge) directions (1 1 0)
    Mesh (non-empty) directions (1 1 0)
    All edges aligned with or perpendicular to non-empty directions.
    Boundary openness (-7.86408e-17 6.4763e-17 0) OK.
    Max cell openness = 1.2645e-16 OK.
    Max aspect ratio = 317.061 OK.
    Minumum face area = 4.71827e-05. Maximum face area = 0.0212115.  Face area magnitudes OK.
    Min volume = 4.71827e-05. Max volume = 0.000180794.  Total volume = 1.  Cell volumes OK.
    Mesh non-orthogonality Max: 30.3678 average: 6.4204
    Non-orthogonality check OK.
    Face pyramids OK.
    Max skewness = 0.492019 OK.

Mesh OK.

End

completely different solution. It produce cinetic energy instead of vanishing
http://dl.dropbox.com/u/3617688/unsVsStru.png

The system/constant files are the same except for this part of fvScheme file

PISO
{
    momentumPredictor no;
    nCorrectors     3;
    nNonOrthogonalCorrectors 3;
    nAlphaCorr      1;
    nAlphaSubCycles 2;
    cAlpha          1;
}

Any idea how can i solve this issue??

[nuovodna]

I solved changing boundary conditions : switching from zeroGradient to fixedValue value uniform (0 0 0) gives me good results.

Special thanks to alberto