FE Hoppy,
Most of the maths just deals with a jet engine as a black pipe (rather than a black box
) with a hole at the front and a hole at the back. The slightly more subtle maths adds front and back surface and local pressure at the "interface" into the equation.
We now are getting into the internal dynamics.... I'll leave that to the experts. About the only thing I'm familiar with in that field is the classic rocket engine with a con-di nozzle with Mach 1 in the throat. Took me enough time to get my mind round it at the time, when actually "playing" with real ones.
CJ