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/sci/ - Science & Math

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5149743 No.5149743 [Reply] [Original]

Question!
Why do fluids travelling at super sonic speeds increase in velocity when they travel through spots of increasing area?
Like the reverse of a nozzle effect.
If you have trouble visualizing, think of a rocket engine where the fuel is being burned it converges tightly at the point it hits super sonic then opens back up to greater area to gain more thrust from the velocity increase, BUT WHY DOES IT DO THIS!!?!?!?!

>> No.5149753

~no one knows~

>> No.5149754

energy force 'charges up' while in the small space and then explodes when it can escape (increase of speed)

>> No.5149755

anyone? please, this is a good conceptual question for people interested in fluid mechanics and thermos.

>> No.5149760

>>5149754

>Why does it do this?

energy is compressed in the smaller space

>> No.5149764

Learn to express yourself clearly.

>> No.5149765

>>5149754
So why doesn't it do the same at lower velocities and only does this for super sonic. It's like Mdot in and Mdot out aren't equivalent in that case and velocity slippage on the nozzle sides don't apply. I feel you're answer didn't answer my actual question

>> No.5149781
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5149781

Maybe this diagram I drew helps you guys. Op here

>> No.5149783

>>5149781
OP here shitty picture is shitty sorry guys. I doubt you can even read it. My apologies

>> No.5149834

>>5149783

Diagram is fine, I understand what you are saying. But unfortunately I can't answer your question.

>> No.5150359

>>5149781
Your assumptions about rhoAV being constant are wrong. Rho is only constant below M=0.3.
For either pipe flow, mdot1=mdot2. Period.

The reason why the rocket nozzle works is that the flow cools down as it flows through the nozzle. This cooling transfers energy within the flow and the energy is used to speed up the flow downstream of the nozzle. Conservation of energy is responsible for the speed increase.

>> No.5150364

>>5149743
Little hint:
Super sonic does not just pertain to sound, but all mechanical waves traveling through air.