Converging diverging nozzle

[ank_gl]

i just started reading about nozzles and turbines in my semester course. i went through converging diverging nozzles. for achieving a supersonic flow, a converging diverging nozzle is used. now a converging section will work as a nozzle only till the flow is subsonic and a diffuser at supersonic flow. that means the maximum velocity obtainable in converging section is speed of sound in the same medium.
also dA/A = [M^2 - 1]dV/V, at Mach 1, section ll not alter the speed of flow.
now consider a converging diverging section. suppose mach 1 is reached at the throat, at mach 1, section ll not alter the speed of flow, then why would the flow become supersonic in the diverging section. i am a little confused about this. since no part of stream can go over mach 1 in converging section, diverging section should act as a diffuser, right?? apparently i am wrong, but i don't know where..
also i was wondering what effect the shape of section might have, i mean concavity or convexity of the nozzle

 

[FredGarvin]

A properly designed CD nozzle will have it's throat at M=1. Compressible theory is where the divergent part starts to work. There are a few funny things that happen because of it. The acceleration of a flow in a divergent section is one of them. Keep reading!

http://exploration.grc.nasa.gov/education/rocket/nozzle.html

 

[ravenprp]

The converging diverging nozzle is a crucial component in supersonic flow systems, such as in jet engines and rockets. As you mentioned, the converging section of the nozzle is responsible for accelerating the flow to the speed of sound, while the diverging section allows the flow to expand further and reach supersonic speeds.

You are correct in noting that at Mach 1, the speed of flow will not change, but the flow can still become supersonic in the diverging section due to the expansion of the flow. This is because the converging section compresses the flow, increasing its density and pressure. When this compressed flow enters the diverging section, it expands and decreases in density and pressure, causing the flow to accelerate to supersonic speeds.

The shape of the nozzle section can also affect the flow. A concave shape in the diverging section can help to smooth out the flow and prevent shock waves from forming, while a convex shape can cause the flow to compress and create shock waves. This can affect the efficiency and performance of the nozzle.

Overall, the converging diverging nozzle is a complex and important component in supersonic flow systems, and understanding its function and design is crucial for the successful operation of these systems. Keep exploring and learning more about nozzles and turbines in your course!