Efficient Rocket Nozzles
Please give a short description (in english (heh)) as to
why a convergent-divergent rocket nozzle is shaped the way it is, and
what having those particular dimensions accomplishes. In other words,
what makes a nozzle efficient?
Dear Chris--In plain English, the convergent part of the nozzle compresses
the mass of the expanding gases from the combustion chamber where the fuel
is ignited. Due to the expansion of the gases in the divergent part of the
nozzle, thrust is created which propels the rocket forward.
The same principle, roughly and minus the heated fuel part, is why an
inflated balloon flies around when you release it from your grip after
blowing it up. When you blow up the balloon, you are creating pressurized
air in the balloon (in place of the combusted fuel in a rocket). The
elasticity in the balloon is acting on the air inside and forces it out the
opening when you release the throat of the neck of the balloon. In case you
are interested, if you do not totally release the balloon and instead hold
on to the intake port and allow the air to escape in a whine or whistle
mode, you are sensing the sonic effects of the escaping air. In certain
cases of fluid flow through a nozzle, you actually achieve the speed of
sound, which is why you hear some of the things you do.
I cannot make it simpler than that. If, however, you seek to understand the
principle a little further, just pick up a basic college book on fluid
dynamics, and it will explain things a bit more. Science can actually be
fun, despite the complicated math, etc., when you look at the applications
upon which the science is based. It always was to me, at least.
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Update: June 2012