Viscous Stability — Lesson 2

This lesson covers the concept of stability analysis in fluid dynamics, focusing on the Orr Sommerfeld equation. It explains the non-dimensional form of the equation and discusses the concepts of viscous stability and stability maps. The lesson also delves into the boundary conditions required to solve the equation and the concept of eigenvalue problems. It further explores temporal and spatial instability, explaining how these concepts predict behaviors in fluid dynamics. The lesson concludes with a discussion on neutral curves and the conditions for viscous and inviscid stability.

Video Highlights

00:46 - Discussion on viscous stability.
04:30 - Conversion of the Orr Sommerfeld equation into non-dimensional form.
05:08 - Explanation of the boundary conditions required to solve the equation.
07:47 - Discussion on the eigenvalue problem.
08:12 - Explanation of temporal and spatial instability.
18:52 - Discussion on the stability map for inviscid flow and flow over a flat plate.

Key Takeaways

- The Orr Sommerfeld equation is used in stability analysis in fluid dynamics. It can be expressed in a non-dimensional form.
- Viscous stability and stability maps are key concepts in understanding fluid dynamics.
- The Orr Sommerfeld equation is a linear 4th order ordinary differential equation that requires four boundary conditions for solution.
- Eigenvalue problems arise in the context of stability analysis, with non-trivial eigenfunctions existing only for certain combinations of parameters.
- Temporal and spatial instability are two types of instability that can be predicted in fluid dynamics.
- Neutral curves of the equation can be plotted to understand the boundary between stability and instability.
- The critical Reynolds number for Blasius flow is 520, with a corresponding alpha delta star of 0.3.