Thermodynamics for Compressible Flows — Lesson 2

Unlike incompressible flows, the kinetic energy in high-speed compressible flows is large and comparable to the heat content of the flow. Moreover, the kinetic energy variations in these high-speed compressible flows are significant enough to affect heat and other fluid properties.​ In other words, we cannot separate the thermodynamics from the kinetics (the motion) and the dynamics (the forces) of the fluid. The motion of a compressible fluid is directly affected by its thermodynamic state, which is itself a consequence of the fluid motion. Therefore, the principles of thermodynamics are a central part of the theory of compressible flow. Engineers rely on these fundamental thermodynamic principles while designing applications such as propulsion systems, internal combustion engines, turbomachinery for power generation systems, etc.


In this lesson, we will discuss the thermodynamics needed for analyzing compressible flows. We will begin with a quick revision of the laws of thermodynamics, subsequently we will introduce the concept of specific heats and entropy relations. We will conclude with the discussion of the "isentropic relations," which will be pivotal in our analysis of compressible flows.

Alternate video link.

Here are the accompanying handout slides for this lesson.