Concept of unsteady flow. Exact Solution of N-S Equation: For unsteady incompressible flow with constant fluid properties: Flow due to plane wall suddenly set in the motion (Stokes’ first problem), Flow due to an oscillating plane wall (Stokes’ second problem), Starting flow in plane Couette motion.
Links:
[1] https://maths.iisuniv.ac.in/courses/subjects/fluid-dynamics-ii-compulsory-paper-6
[2] https://maths.iisuniv.ac.in/academic-year/2015-2016