Tangential velocity in a 3D expanding annulus not ZERO. Please help!
 

I am trying to study the air flow inside an expanding annulus. The inlet velocity is purely axial. As this is an annulus (axisymmetric geometry), it is essential that the 3D simulation results give zero tangential velocity. Howver, I am getting a value to the order of 10^-3, which can not be correct. The axis is defined correctly in the fluid panel. I have run the simulations in many different grids but have not been able to solve this issue. Please help.