So I am learning for thermodynamics now and there is one thing that is bugging me. In the book it shows a laval nozzle (very simplified) and a diffuser.
(a is the speed of sound)
According to those images and its explanation that would mean, if I make a paper cone with a hole in it and blow into it, at the hole speed of sound would be reached. That is obviously not the case. So what am I missing?
At the beginning it says "Isentropic flows" but how does one actually know that the flow is isentropic? Or is it because of turbulence?