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Research Toward Quieter Jet Engines (1970)
🕑 Added 2021-11-26 16:11:12 +0000 UTCIn this installment of NASA's Aeronautics and Space Report No. 67 we see the research that was going into trying to reduce the noise of jet aircraft around 1970.
Comments
BobC
The greatest engine noise reduction improvements came, in order of decreasing effect, from 1) increasing the bypass ratio (providing an "air blanket"), 2) adding serrations to the core section exhaust (breaking up exhaust resonances and pushing the sound energy into short-range ultrasonic vortices), and 3) improved turbine blade designs (via CFD). Split-spool designs (which run the compressor, or sections of the compressor, at different speeds than the power turbine) were also effective, but the added mechanical complexity was problematical until ever-greater engine inlet diameters made it mandatory in order to keep inlet blade tip speeds subsonic. Other noise-quieting techniques came from changing both the landing and take-off paths combined with extreme wing designs that permitted greater lift at lower relative thrust levels.
Aaron Nadler
it would be interesting to have commentary by AgentJayZ (A Canadian jet youtuber)
Fred Patton
Funny though that the ultimate solution was the high-bypass turbofan, something that doesn't seem to have been thought of at this pint. When I was a kid going to airshows at Moffett Field in California, a few times NASA Ames Research Center trotted out the Quiet Short-Haul Research Aircraft, a high wing, 4-engine jet that would wow the crowd with the most incredible short takeoff and landing demonstrations in virtual silence.
Michael S Wilhelm
They really succeeded. I live under an approach/departure path at a major airport, and you can pretty much tell how old an airliner is by how loud (or quiet) the engines are.
