lehpron
Posts: 6846
Joined: Tue Jul 10, 2001 3:42 am

Rocket Nozzle Shapes?

Sun Jan 02, 2005 4:31 am

Is there a way to determine the shape of rocket nozzles, they almost appear like a steep parabolic. Even the outlet sidewalls have slope, they are not parallel to the direction of motion.
The meaning of life is curiosity; we were put on this planet to explore opportunities.
 
MD11Engineer
Posts: 13916
Joined: Sun Oct 26, 2003 5:25 am

RE: Rocket Nozzle Shapes?

Sun Jan 02, 2005 7:25 am

Most rocket exhaust nozzles are Laval nozzles (Laval, Swedish 19th century engineeer, invented and first used this type of nozzles in steam turbines).
The idea of any nozzle is to convert potential energy of a gas (pressure) into kinetic energy, e.g. give the gas a velocity as high as possible.
Laval nozzles work on the principle that the throat area dimensions let the gas at a given combustor pressure reach the speed of sound in the throat. The cone behind is dimensioned, that the gas will expand further and exceed the speed of sound. The shape of the cone (the angle of the opening) is mostly determined by the pressure difference between the throat and ambient. As a result, rocket nozzles used within the atmosphere tend to be narrower than those used in a vacuum.

Jan
Je Suis Charlie et je suis Ahmet aussi
 
lehpron
Posts: 6846
Joined: Tue Jul 10, 2001 3:42 am

RE: Rocket Nozzle Shapes?

Sun Jan 02, 2005 3:07 pm

>>" The shape of the cone (the angle of the opening) is mostly determined by the pressure difference between the throat and ambient."<<

Ah, you literally hit the head of the nail. I imagine there is a formula to describe this or could it be some kind of arcsine of ambient above throat pressure?

That makes so much sense by itself though, and I thought it was such a f*cking mystery; thanks Jan.  Big thumbs up

The meaning of life is curiosity; we were put on this planet to explore opportunities.
 
EMBQA
Posts: 7798
Joined: Sat Oct 25, 2003 3:52 am

RE: Rocket Nozzle Shapes?

Tue Jan 04, 2005 2:22 am

If you get a chance watch October Sky. It's a true story about a group of young model rocket fans, one of which went on to NASA. They touch on nozzle design as a control issue.
"It's not the size of the dog in the fight, but the size of the fight in the dog"
 
lehpron
Posts: 6846
Joined: Tue Jul 10, 2001 3:42 am

RE: Rocket Nozzle Shapes?

Mon Feb 07, 2005 10:07 am

Follow-up question: Usually a hot gas come out of a rocket nozzle so the shape is due to pressure (thank you MD11Engineer)

What is the exhaust is a plasma? It's hot enough to be ionic and thus would need to be controled by magetic solenoid fields, but is there a pressure difference to cause a need for a traditionally shaped rocket nozzle? Or is the solenoid shaped that way?


BTW, I'm watching October Sky right now -- never seen it and have no prejudgements -- this should be interesting.

My friend who let me borrow the disk asked me how I can be into SciFi movies like Stargate, Event Horizon, Contact, etc and still be in aeronautical engineering rather than astronautical. I don't know what to tell him.

Guilty pleasure I guess.  Wink/being sarcastic
The meaning of life is curiosity; we were put on this planet to explore opportunities.

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