A well-known exact solution to the Navier-Stokes equation (4.38) is the unsteady circulating motion [15] Where K

Question:

A well-known exact solution to the Navier-Stokes equation (4.38) is the unsteady circulating motion [15]
Where K is a constant and ν is the kinematic viscosity. Does this flow have a polar coordinate stream function and/or velocity potential? Explain. Evaluate the circulation Γ for this motion, plot it versus r for a given finite time, and interpret compared to ordinary line vortex motion.