Flow in the Wake of a Flat Plate — Lesson 2

This lesson covers the concept of free shear flows, focusing on the flow near a wake behind a flat plate of finite length. It explains how the wake develops downstream of the flat plate and how the velocities become self-similar about three lengths downstream. The lesson also discusses the concept of velocity defect and how it is calculated. It further delves into the boundary layer equation and how it can be simplified in terms of velocity defect. The lesson concludes with the application of the drag formula for a flat plate to find a constant in the velocity defect expression.

Video Highlights

00:35 - Explanation of the wake development downstream of a flat plate.
03:02 - Explanation of the boundary layer equation and its application to free shear flows.
06:20 - Explanation of the expression for velocity defect.
09:52 - Explanation of the Reynolds number.
13:47 - Discussion on an example problem of air issuing from a narrow slot and forming a 2D laminar jet.
22:21 - Discussion on an example problem of air flow past a slender 2D body.

Key Takeaways

- Free shear flows near a wake behind a flat plate of finite length are non-similar immediately downstream but become self-similar about three lengths downstream.
- The velocity defect, which is the difference between the free stream velocity and the velocity at a given point, is maximum at the center line.
- The boundary layer equation can be simplified in terms of the velocity defect.
- The drag formula for a flat plate can be used to find a constant in the velocity defect expression.