Re: leaking planes Re: [really OT] (was: Re: [OM] OM] OT - Titanium)

[gary edwards]

Any supersonic jet will have a pattern of oblique shock waves originating 
generally at the nozzle exit plane (the term "jet" is used here to refer to 
the stream of fluid discharged from the nozzle.)  These shock waves reflect 
("bounce") from the jet boundary back into the jet in the characteristic 
diamond pattern.  The angle formed by the diamonds is related to the flow 
Mach number - faster=longer diamonds.  These shock waves are visible in some 
cases due to the different index of refraction across the shock wave.  Jet 
engines that do not produce a supersonic exhaust jet do not display shock 
diamonds.  Most engines produce supersonic jets only when operating in 
afterburner ("reheat") and the articulated nozzle petals are closed down to 
form a convergent-divergent nozzle.  All rocket engines have shock diamonds 
but in many cases (like the classic slow-motion Saturn V launch sequence), 
the diamonds are not visible due to the incandescence of the exhaust gases. 
The incandescence doesn't allow you to see through the jet.
OM Content: When photographing jet aircraft in afterburner you may have a 
better chance of capturing the shock diamonds if the exhaust jet is somewhat 
backlit.  That is how we photographed control rocket simulators that used 
cold nitrogen as a working fluid.
Gary Edwards


> From: Chris Barker <cmib@xxxxxxxxxxx>
> Reply-To: olympus@xxxxxxxxxxxxxxx
> To: olympus@xxxxxxxxxxxxxxx
> Subject: Re: leaking planes Re: [really OT] (was: Re: [OM] OM] OT - 
> Titanium)
> Date: Tue, 10 Aug 1999 13:53:45 +0200
>
> >on my page shortly thereafter. What causes the diamonds in the exhuast
> >plume?
> >
> >/Acer Victoria
> All "decent" engines have them (the Tornado's RB199 does not) - nb personal
> prejudice, not scientific observation.  I believe that it is the formation
> of Mach cones in the exhaust that shapes the flame into 'V' or diamond
> shapes.
>
> Chris
>
> _______________________________________
> Chris Barker <><       mailto:cmib@xxxxxxxxxxx
> Box 2, Officers' Mess,
> RAF Brueggen, BFPO25, UK.
>
>
>
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