Reaching Mach 1: Detecting Sonic Velocity in a Convergent Nozzle

[PhysicoRaj]

How do you know if a convergent nozzle has reached the exit velocity of mach 1? Suppose a convergent nozzle is connected to a blower, and gradually the blower air velocity is increased, would any phenomenon be helpful in detecting when the nozzle exit velocity is sonic, which can be heard or seen?
Thanks.

 

[Bobbywhy]

Possibly I misunderstand what you're asking. Have you read this?
http://en.wikipedia.org/wiki/De_Laval_nozzle

It may help answer your question. If not, then please post here again.

Cheers, Bobbywhy

 

[PhysicoRaj]

Ya I have read De Laval nozzle on wiki. But it does not say how to know when the velocity at the throat will be sonic(mach 1).
To make it simpler, my question is " Is there any effect or phenomenon that occurs when the velocity of air at the throat of the CONVERGENT nozzle reaches mach 1, like a unique sound or something that can be seen, or felt?"
Thanks..