Listen to this video. It's a NASA simulation, based on real acoustic and atmospheric physics, that compares the noise generated by a 777-class airliner with that created by a future blended wing-body (BWB - NASA calls it hybrid wing-body, or HWB) configuration.
They are not recordings. They are complex simulations created via NASA's widely used ANOPP noise-prediction computer code. ANOPP is used to calculate the source noise from the engines and airframe, while other codes model the atmospheric absorption and even the ground reflection.
You just have to listen to the first in each pair of "auralizations" to realize how realistic they are: the simulations of what NASA calls the "state-of-the-art" (SOA) tube-and-wing airliner - a 777-class aircraft with GE90-class engines - sound just like the real thing, with all the complex tones you hear in the fan, jet and airframe noise of a landing aircraft.
Because the HWB's twin engines are mounted above the aircraft, and are shielded from the ground by the body and wing, it is dramatically quieter. In numbers, the SOA's approach noise, observed from the runway centerline, is 99.4 EPNdB; the HWB's is 83.9 EPNdB.
That's a reduction of 15.5dB - 3dB is a halving of noise level, but how much quieter the HWB would be only becomes meaningful when you can hear the difference (turn up the volume, if you can).
One of the goals of NASA's aeronautics research is to reduce the noise generated by commercial aircraft to levels where the annoyance is contained entirely within the boundary of the airport. For a 2025-timeframe HWB, NASA is aiming for a cumulative 42dB below Stage 4 limits - enough to reduce the airport noise footprint to just 8% of its Stage 4 size.
Unveiling the "auralizations" in Fort Worth, Dr Stephen Rizzi, senior research engineer with NASA Langley's structural acoustics branch, said the next step is to run the HWB noise simulations with open-rotor engines. These will use acoustic data generated by tests of second-generation open-rotor blades conducted by General Electric, NASA and the FAA.