ABSTRACT
Although all fluids are to some extent compressible, only gases show a marked change of density with a change of pressure or temperature. Even so, there are many examples of the flow of gases in which the density does not change appreciably, and theory relating to constant-density fluids may then adequately describe the phenomena of flow. In this chapter, however, we turn our attention to the flow of gases in which changes of pressure and velocity are associated with significant changes of density.
