fuction for ddt(n) which n is normal surface vector
 

Dear Foamers

I'm writing an acoustic code for dynamic mesh case in a centrifugal fan. I use turbDyMFoam with movingWallVelocity BC at blades.
In one of the terms of this code, ddt(n) is needed, witch n is the normal vector of the blade surfaces that move around. I know the functions for normal vector of the patches but for its time derivative I don't know how to calculate them.
Another question is, Is there any function that could calculate velocity of the faces of the blade (which use dynamic mesh dict and movingWallvelocity) ?!

Thank you
Mohammadreza Shetab

Hello Foamers and Mohammadreza,

I have the same problem now and read many topics here in cfd-online.com, but did not found any solution. I hope for a hint, because my tryings were not successfully.

So how to calculate the surface normal velocity of a free design surface?

For example on the rotor in the picture which is uploaded here, the rotation vectors are shown. So the normal surface velocity on the x-y plane must be zero, because there is no moving in the direction of the surface normal.