Isentropic flow

Summary

An isentropic flow is a flow of a fluid in which the entropy of each fluid particle stays constant. This holds when there is no heat exchange and no dissipation. It is the standard model of compressible flow away from shock waves and boundary layers. For an ideal gas it gives algebraic relations between pressure, density, temperature and Mach number. These reduce many problems, such as flow in nozzles, to one-dimensional calculations.