A viscous fluid is contained between two infinitely long, vertical, concentric cylinders. The outer cylinder has a radius ro and rotates with an angular velocity v. The inner cylinder is fixed and has a radius ri. Make use of the Navier–Stokes equations to obtain an exact solution for the velocity distribution in the gap. Assume that the flow in the gap is axisymmetric (neither velocity nor pressure are functions of angular position u within the gap) and that there are no velocity components other than the tangential component. The only body force is the weight.
Please answer with a derivation of the Navier Stokes equations in cylindrical coordinate system with the reasons you are able to cancel out terms.