ORIGINAL: Henke Torphammar
I think it's the other way around. Smaller outlet will increase the power. Look at a fighter jet taking of, the tailcone is closed when throtteling up. I bet Frema has the correct answer :-)
A smaller diameter exhaust nozzle would cause the gasses to exit faster – i.e. the only way a fixed volume of gas can exit through a smaller aperture within the same timeframe, is if that gas is moving faster. If the power were to remain constant, then this increase in gas speed must come to the detrimental cost of thrust.
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Just like a conventional propeller, Power = Thrust x Pitch-speed. If the Power remains constant, then for the Thrust to increase (by increasing the diameter of the propellor), the Pitch-speed must decrease (by decreasing thepitch of the propellor)
Everything in a gas-turbine is probably highly-balanced/matched though, so perhaps you can’t simply increase exhaust nozzle diameter without also changing something else, but nevertheless, the principle is right. :-)
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