sonic section before and after a shock !!

Hi every body

A sonic area in a CD nozzle can only exist when M=1 . It is the throat of the nozzle . When M=1 , we have a shock .

Imagine together that we have a normal shock NS just before the exit of the nozzle . My question is :

Is it true to say that we have a sonic throat upstream NS , it 's area is A1* ? ( with A1* = At , At is the throat of the nozzle )

Is it true to say that we have a sonic throat downstream NS , it 's area is A2* ?

At my opinion , we can only talk about a sonic area A* exactly where the normal shock takes place ( not before , not after NS) .

Thanks you for help , it seems that i am confused

Best Answer


  • Hello,

    If there is a normal shock in the diffuser section of the CD nozzle:

    1. The flow upstream till the throat is subsonic
    2. At the throat, it is sonic i.e. M=1
    3. Beyond the throat, the flow accelerates to supersonic till the Normal shock
    4. Right after the normal shock, the flow is subsonic.
    5. The flow further decelerates till the end of the nozzle.

    I hope this helps.



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