Nozzle shapes

Nozzle shapes

Post by Raphael Tymows » Fri, 27 Oct 1995 04:00:00



Could someone please explain to me why the nozzles on rocket engines are
diverging, while those on jet aircraft are converging? Does it have anything
to do with the velocity of the exhaust?

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Nozzle shapes

Post by Louwe » Sat, 28 Oct 1995 04:00:00


: Decent nozzles on rocket motors are both converging and diverging. The
: relative velocities of gases are:  inside the chamber - subsonic, somewhere
: along the converging section - reaches speed of sound, diverging section -
: all supersonic.

In this way the pressure & temperature 'energy' are converted to kinetic
energy. The combustion gasses are accellerated further then when just using
a hole. Because thrust is proportional to exhaust velocity, you want this
velocity to be as high as possible.

Jeroen Louwers    

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Nozzle shapes

Post by Bill Nels » Sat, 28 Oct 1995 04:00:00


: Could someone please explain to me why the nozzles on rocket engines are
: diverging, while those on jet aircraft are converging? Does it have anything
: to do with the velocity of the exhaust?

Decent nozzles on rocket motors are both converging and diverging. The
relative velocities of gases are:  inside the chamber - subsonic, somewhere
along the converging section - reaches speed of sound, diverging section -
all supersonic.

Of course, this assumes that there is enough chamber pressure to produce
supersonic flow.

Bill

 
 
 

Nozzle shapes

Post by Streu » Sat, 28 Oct 1995 04:00:00



:Of course, this assumes that there is enough chamber pressure to produce
:supersonic flow.
:
:Bill

Ummmm...well actually, and pressure differential can produce supersonic
flow. I have a bipropellant motor that runs on gaseous oxygen and gaseous

Umm....lets see, 1..2..3..4..5..6 mach diamonds...well..there should be a
sixth but it's a little foggy. In theory, a pressure gradient of 1 psi can
produce supersonic flow. As long as the nozzle is designed correctly of
course.

: Because thrust is proportional to exhaust velocity, you want this
:velocity to be as high as possible.
:

Or just boost the chamber pressure so high as to MAKE it be efficient!! :)
 Hey Jeoren!! Hows it going? Any word on the carbon-carbon? The sounding
rocket motor is FINALLY advancing (very) slowly. But what else can i ask
for? It could just NOT be moving. I should have some pics for you soon
(crossing fingers). Ummmm....ive got some test's under my belt on a NEW
fuel for the HTPB/N2O ideas you and i both have. Nice Isp boost i must
say!! Needs development though. Email me for more specifics.

Cheers,

Brian Streufert

 
 
 

Nozzle shapes

Post by Bill Nels » Mon, 30 Oct 1995 03:00:00



: :Of course, this assumes that there is enough chamber pressure to produce
: :supersonic flow.

: Ummmm...well actually, and pressure differential can produce supersonic
: flow. I have a bipropellant motor that runs on gaseous oxygen and gaseous

: Umm....lets see, 1..2..3..4..5..6 mach diamonds...well..there should be a
: sixth but it's a little foggy. In theory, a pressure gradient of 1 psi can
: produce supersonic flow. As long as the nozzle is designed correctly of
: course.

Which was basically my point. If the nozzle is not designed properly, then
there will not be supersonic flow.

For example, if you leave out the converging section, then it takes a much
higher chamber pressure to get supersonic flow in the diverging section.

Bill

 
 
 

Nozzle shapes

Post by The Silent Observ » Mon, 30 Oct 1995 03:00:00




Quote:

>> For example, if you leave out the converging section, then it takes a
much
>> higher chamber pressure to get supersonic flow in the diverging
section.

>> Bill

>If you leave out the converging section, it is impossible to
>achieve supersonic flow in the nozzle.

I think you're incorrect there -- there have been at least a couple
motors with supersonic exhaust, including both the US Rockets nozzleless
designs, and at least one medium-small commercial 4-chamber liquid motor
(this might have been used in the X-1 or X-1A) that had no convergent --
rather, they (apparently) depend on shock wave effects around the exit
to do the job that would be done by the convergent in a more
conventional motor.

If the burn rate and/or propellant flow rate is high enough, the
combustion can produce supersonic flow directly.

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Nozzle shapes

Post by Todd Peter » Wed, 01 Nov 1995 04:00:00


Quote:
> >If you leave out the converging section, it is impossible to
> >achieve supersonic flow in the nozzle.

> I think you're incorrect there -- there have been at least a couple
> motors with supersonic exhaust, including both the US Rockets nozzleless
> designs, and at least one medium-small commercial 4-chamber liquid motor
> (this might have been used in the X-1 or X-1A) that had no convergent --
> rather, they (apparently) depend on shock wave effects around the exit
> to do the job that would be done by the convergent in a more
> conventional motor.

> If the burn rate and/or propellant flow rate is high enough, the
> combustion can produce supersonic flow directly.

Hmm.  Unless the combustion occurs in a supersonic flow (not in
a rocket) then supersonic combustion is known as detonation.  Generally,
not a stable process.  Could you explain technically how it is possible
to achieve supersonic flow without a convergent nozzle?  Shock waves
only slow a flow down.  Expansion waves are only effective above
Mach 1, that I know of.  I can't see how it could be done, but
of course that doesn't mean it isn't possible.
Todd