Re: Some Turbofan Questions

From: (Wolfgang Wohlers)
Organization: RWTH -Aachen / Rechnerbetrieb Informatik
Date:         07 Jul 96 14:09:01 
References:   1
Followups:    1 2
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Hallo !

>   What proportion of the thrust is generated by the
>bypass air and what proportion comes from the exhaust
>gas generated in the core of the engine?  I realise this
>question may not have a simple answer, as the bypass air
>mixes (next question, how much does it mix?) with the exhaust gas,
>but give me an estimate anyway.
I will try, though I am not sure about it: Today turbofans have bypass
ratios of about 7. If you say that the change in velocity is about the
same for bypass and core air (this is not exact of course) you get 7/8
of the thrust through the bypass and 1/8 thruogh the core air. I am
not sure how much faster the core air is, but I think most the thrust
is provided by the bypass air.
>   Also, are there any turbofans with more than one fan (not
>compressor) stages?
Not to my knowledge.
> And while I'm still in question mode,
>did early commercial jet engines (Comet, 707 etc) use
>any bypass air, or did it all go through the core?
They  were turbojet and didn't have any bypass air.