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Can any one explain in detail about drag increase in supersonic speed

Why and how drag increases in Blunt shape nose cone to compare with Sharp nose cone at supersonic speed?

Ryan

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- Thread starter vincentryan
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- #1

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Can any one explain in detail about drag increase in supersonic speed

Why and how drag increases in Blunt shape nose cone to compare with Sharp nose cone at supersonic speed?

Ryan

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minger

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I still can't intuitively grasp how a supersonic flow works in a converging-diverging nozzle works.

After the choke point, the area is increasing AND the velocity is increasing. To top it all of, the density is decreasing in a flow that is going fast enough to be considered compressible...sigh..

- #6

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I still can't intuitively grasp how a supersonic flow works in a converging-diverging nozzle works.

After the choke point, the area is increasing AND the velocity is increasing. To top it all of, the density is decreasing in a flow that is going fast enough to be considered compressible...sigh..

It can be explained through the manipulation of the mass conservation equation:

density*velocity*area = constant

Taking the derivative and manipulating it to get d density/density + d velocity/velocity + d area/area = 0, and using the definition of the speed of sound/Mach number...you end up with this equation:

d velocity/velocity * (mach number^2 - 1) = d area/area

This is known as the area-velocity relationship. So as you can see, for mach numbers less than 1, you get a negative sign for the value, thereby getting that relationship used in INcompressible flow where velocity slows down when area goes up, and vice versa.

When you start to go above Mach 1, the sign becomes positive, and both area and velocity essentially change in the same direction.

- #7

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I still can't intuitively grasp how a supersonic flow works in a converging-diverging nozzle works.

After the choke point, the area is increasing AND the velocity is increasing. To top it all of, the density is decreasing in a flow that is going fast enough to be considered compressible...sigh..

Why should you intuitively grasp supersonic flow? It's not something in your everyday tactile experience!

Do you have an intuitive understanding of low reynolds flow? Nope. You are way too large to experience 'atoms' of air hitting you. You can only feel a continuum.

Your 'intuition' will come through understanding of the mathematics of the flow.

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