[AR] Nozzle shapes
- From: Ben Brockert <wikkit@xxxxxxxxx>
- To: "arocket@xxxxxxxxxxxxx" <arocket@xxxxxxxxxxxxx>
- Date: Tue, 12 Nov 2013 12:35:45 -0700
Anyone have further info to back this up, or Russian nozzle design
logic translated into English?
From a powerpoint on nozzles by D. R. Kirk of FIT:
Q: Why do U.S. nozzles look more like a polynomial contour and Soviet
nozzles look more conical?
A: (Jim Glass, Rocketdyne)
Interestingly, Soviet nozzle designs have a 'different' look to them
than typical US designs. US designs are ‘truncated Rao optimum’
bells, usually designed by method-of-characteristics methods. Soviet
nozzles, to US eyes, look more conical than ours. Ours have that nice
‘parabolic’ look to them - less conical. One would suppose the
Russians are fully capable of running M-O-C and CFD codes and thus
their nozzles, if optimum, should look ‘just like’ ours. Since they
don't, I've always wondered if they know something we do not. In my
experience, the US is better at combustion engineering (minimal C-star
losses) but has fairly substantial losses in the nozzle (aerodynamic
losses). The Russians tend to reverse this, throwing away huge gobs
of energy due to incomplete combustion and then using a very efficient
expansion process to get some of it back. The bottom line is both
design approaches appear to yield roughly the same Isp efficiency...
One wonders what would happen if one were to mate a US combustor to a
Russian nozzle…
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