Understanding Stokes First Problem — Lesson 1

This lesson covers the concept of Stokes first problem in fluid dynamics. It explains the scenario where a stationary plate in an infinite stationary fluid medium starts moving impulsively, leading to a velocity profile that is a function of one special coordinate and time. The lesson further discusses the concept of penetration depth, which is the distance up to which the effect of the moving plate penetrates inside the fluid domain. It also elaborates on how to derive the governing equation for Stokes first problem, and how to convert this partial differential equation into an ordinary differential equation using the similarity variable approach. The lesson concludes with the calculation of the shear stress distribution inside the fluid domain and at the wall.

Video Highlights

00:50 - Explanation of Stokes first problem, involving a stationary plate in an infinite stationary fluid medium that starts moving impulsively.
04:34 - Derivation of the governing equations for Stokes first problem using the continuity equation and momentum equations.
15:04 - Explanation of how to convert the partial differential equation into an ordinary differential equation using the similarity variable approach.
33:34 - Calculation of the velocity distribution using the error function.
36:18 - Discussion on the concept of penetration depth and shear stress distribution .

Key Takeaways

- Stokes first problem deals with the unsteady flow problem where a stationary plate in an infinite stationary fluid medium starts moving impulsively.
- The velocity profile generated due to this movement is a function of one special coordinate and time.
- The penetration depth, which is the distance up to which the effect of the moving plate penetrates inside the fluid domain, is proportional to the square root of time.
- The governing equation for Stokes first problem can be derived and converted into an ordinary differential equation using the similarity variable approach.
- The shear stress distribution inside the fluid domain and at the wall can be calculated using the derived equations.