Unsteady annular flows? 

(a) Obtain a solution to the Navier-Stokes equation for the start-up of axial annular flow by a sudden impressed pressure gradient. Check your result against the published solution. 

(b) Solve the Navier-Stokes equation for the unsteady tangential flow in an annulus. The fluid is at rest for t < 0. Starting at t = 0 the outer cylinder begins rotating with a constant angular velocity to cause laminar flow for t > 0. Compare your result with the published solution.