Thank you, everyone, for your inputs. I am a bit confused about what to do...
So I tend to agree with you that forces because of axial velocity might be balanced.
But I think If I only consider torque due to circumferential force then I might be overestimating the value.
Because if you think...
I have a problem as shown in the figure
So assume there is a cylinder rotating inside a stationally wall. There is a viscous fluid in between the gap of cylinder wall and outer stationary wall, similar to bearing.
The fluid has some velocity in axial direction also
the outer wall of cylinder...