# Chapter 4 - Chapter 4 Introduction to Compressible Flows We...

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Chapter 4 Introduction to Compressible Flows
We shall consider flows of compressible fluids or gases Gases travelling faster than the speed of sound (supersonic) behave quite differently from the gases travelling slower than the speed of sound (subsonic) We shall develop expression for sonic velocity through an arbitrary medium speed of gas The Mach number ( ) is introduced speed of sound as a key parameter
Let us consider a one-dimensional system. Only one component of velocity is considered. Consider an infinitesimal pressure wave travelling in a long constant-area tube filled with a compressible fluid and having a piston at one end (see Figure 4.1) At a certain instant the piston is given an incremental velocity dV to the lef The fluid particles next to the piston are compressed a very small amount as they acquire the velocity of the piston.
V: velocity of fluid a: Wave front velocity
Wave front: A wave front is observed to propagate through the fluid at the characteristic sonic velocity of
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