Why the axial velocity of the wall using rotatingwallvelocity BC isn't zero?
 

Hello,
I using rotatingwallvelocity on the blade of a turbomachinery.The relative part in the file of 0/U is :
.
.
.
BLADE1
{
type rotatingWallVelocity;
origin (0 0 0);
axis (0 0 1);
omega 1537.70488;

}

BLADE2
{
type rotatingWallVelocity;
origin (0 0 0);
axis (0 0 -1);
omega 1537.70488;
}

}
So the axis is z-axis.Then I run the commend "foamToVTK -time 0" to get the VTK file.Openning the VTK by paraview, I find that Uz on BLADE1 and BLADE2 isn't zero.Just like that:
Attachment 27055
But in reality, if a object rotates with a axis, its axis velocity will be zero.

Am I using the BC condition wrong? Or there is a bug about rotatingwallvelocity BC. I can't find the answer by Google.Hope someone help me.

Best regards
Zhiyuan