Elements of Compressible Flows — Lesson 2

Have you ever used a compressed air canister? The canister body gets cold after spraying. Why does that happen?

Breaking the sound barrier was a monumental event in the history of aviation. In such flights, the aircraft travels at speeds that are greater than the speed of sound! You might have heard about the phenomenon called a “sonic boom.” It happens when an aircraft is flying at really high speeds comparable to the speed of sound. A sharp audible BOOM or CLAP is heard during this flight. In such flying conditions, what do you think happens to the air around the aircraft? Here is how an aircraft pilot explains breaking the sound barrier.

The above phenomena occur because of the compressible nature of fluids. Certain fluids can be compressed tightly while others cannot. This is primarily dependent on the variation of fluid density. In this lesson, we will understand fluid compressibility and learn certain fundamentals of compressible flows. We will discuss why certain fluids can be compressed and explain the different flow regimes in compressible flows such as subsonic, transonic, supersonic and hypersonic. We will also understand the different types of shock waves that are generated in the fluid during these flow regimes.

Alternate video link.

Here are the handout slides for this lesson.