Compressible FlowΒΆ
Compressible flow occurs when the density changes significantly in the course of a flow. In many cases, it is possible to model flow as incompressible, even for gasses! However, if the Mach number exceeds about 0.3, then the density of the flow will change significantly and the effects of compressibility must be considered.
In propulsion applications, the thrust equation:
tells us that we want the largest possible mass flow rate and exit velocity of the flow. This is accomplished by a converging-diverging nozzle and the flows we are interested in will be accelerated into the compressible flow regime.
The following sections in this chapter describe the major equations relevant for compressible flow in a nozzle, starting with the definition of a few new properties we will need.