# Air flow in Convergent divergent nozzle

i understood the air flow properties variation in convergent divergent / condi nozzle or laval nozzle for subsonic flow based on the formula, for a incompressible flow :

density * Area * velocity = constant
as the total pressure in the flow is constant dynamic pressure is minimum at the throat and static pressure is much more.

for subsonic flow, as the area decreases at the throat of the nozzle, velocity increases and after the throat as the area increases, velocity decreases, that is how velocity is maximum at the throat of the condi/laval nozzle.

once speed of the flow is slowly increased as the velocity of the flow reaches the velocity of sound i.e. M=1, the compressibility effects come into picture, how the flow properties i.e. velocity and dynamic pressure variations change.

1. it is said that for supersonic flow the velocity at the throat decreases where as the velocity increases as the throat diverges, why is it so, why the velocity variations are opposite to that of subsonic flow ?

2. And when does the shock wave forms in the condi nozzle ? how the shock wave forms if at all it forms ?

3 why the velocity in condi nozzle never exceeds M =1 ?
can any one please explain me in simple terms rather than math formulae.