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Coming from a slightly related question, I want to know what is the speed of the gas in the core of a jet engine, after combustion but before the first turbine stage.

I'll just pick a random example: Rolls Royce Trent XWB.

Also, I don't know if the speed in the core is equal to the speed at the exhaust. I just want to be clear that it's the core air speed I'm interested in here.

I realize core air speed might vary with thrust and flight level. In that case I think the most sensible thing to do is choose some typical flight conditions during cruise.

DrZ214
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    Would this answer your question? – Peter Kämpf Jan 26 '21 at 04:11
  • @PeterKämpf It's a very good chart but it doesn't say what engine it's for, and also what operating conditions (cruise or static on the ground). From the looks of it, it might be an old turbojet. I don't know if all turbo engines have the same or very similar core conditions for all 3 parameters, especially if talking over the whole history of jets. – DrZ214 Jan 26 '21 at 04:39
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    @PeterKämpf I just read all 13 pages of that pdf, "3_engine_fundamentals". It's very well written, but I can't find an author, publisher, or date of publication anywhere. Is it an excerpt? If so, what and where is the full text? BTW page 6, The overall pressure ratio ... is approximately 9.5:1. That makes it sound very dated. Modern big jet engines get 20:1 compression ratio or more, and pressure ratio will be greater according to P1/P2 = (V1/V2)^gamma. – DrZ214 Jan 26 '21 at 07:55
  • In addition, i think i found an error on page 12. centrifugal flow compressors operate at somewhat lower pressure ratios than axial flow compressors. The rule of thumb I've heard here on this site is that centrifugals typically have 4:1 compression ratio, but axial stages have more like 1.2:1. And those are compression ratios, so pressure ratio of centrifugals will be even greater according to that same equation. – DrZ214 Jan 26 '21 at 07:57
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    All your comments are correct. As far as I know, the diagram is made by RollsRoyce and is not for a specific engine, but shows generic data maybe from the Seventies. Regarding centrifugal compressors: Per stage they have much higher ratios than an axial compressor, but overall the compression ratios of jet engines with radial compressors are much lower than those with axial compressors. I think that is what the PDF means. – Peter Kämpf Jan 26 '21 at 08:04

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