Effects of Compressibility

Abstract

All fluids in nature are compressible, that is, if enough pressure is applied on a macroscopic fluid element, its volume decreases. Gases are usually much more easily compressed than other fluids and this is probably the reason that the regime of compressible flows is usually known as gas dynamics. We have, however, discussed in Chap. 2 the conditions under which the assumption of incompressibility of a particular flow is a good approximation and because it simplifies the equations considerably, we could consider there a number of important incompressible flows. The explicit conditions were summarized in Sect. 2.4.1, even though various considerations regarding this issue appear in other places of Chap. 2 as well. Moreover, it may happen that these explicit conditions for incompressibility are not met, even approximately, but it is still useful to assume incompressibility. Such is the case when the physical phenomena under study do not rely at all on the fluid property of compressibility.