flow rate in the case of subsonic and supersonic flow ( CD NOZZLE)

aero2020aero2020 Member
edited August 2020 in Fluid Mechanics

Hi every body :

Are you ok with me that in the absence of leakage , also in the case of isentropic flow ( no friction , no drop in total pressure etc.) the mass flow rate is constant between inlet and outlet ? that means : Ae me (dot) =As ms (dot)?

My problem : i have found in a book what follows : (it is not clear for me )

1/ after a shock in the throat , the flow becomes subsonic , it is isentropic so the Mach number at the exit of the divergent remains the same as the Mach calculated before the shock .

my question is why ? is this conclusion was deduced from the mass flow conservation ? I don't see the physics behind it .

Remark : M=cte that means A/Ac=cte

2/ We have a shock at the divergent and the flow is considered sonic at the throat .We can so suppose that the flow rate at the outlet is the same ( as this found before the shock ) !

It is not clear ! At my opinion , the shock is irreversible so the flow rate can not be the same as we have a shock in the divergent ! Conclusion : it is not possible to consider ( in the presence of a shock) the same flow rate (found before the shock)

Can you help me please !

Kind regards

(sorry for english mistakes 😊)

Best Answer


  • Hi freinds ;

    In otherwise , my question was :

    Consider a compressible flow in a CD nozzle ( regardless an eventual change in the flow regime) :

    In which case :

    1/ The Mach remains constant ( in some section A/Ac)?

    2/ The flow rate remains constant across some section A/Ac ?

    Thank you very much for your assistance

  • Ok thank you very much

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