Efforts to bring supersonic jets back to the skies could be hampered by a new finding: rows of tightly-spaced buildings could make disruptive sonic booms worse.
Twenty years since the retirement of Concorde, a host of companies are bringing supersonic aircraft back to the market. But their use may be limited by disruptive sonic booms – the US Federal Aviation Authority currently prohibits commercial aircraft from travelling faster than Mach 1 over land and for a certain distance offshore. Some companies have tried to make low-boom supersonic aircraft.
Now University of Lyon researchers have conducted simulations comparing how sonic booms might differ when they take place over a single building, two neighbouring buildings, or multiple buildings spaced at regular intervals.
"This paper is the first study to address the propagation of the boom in an urban environment," said co-author Didier Dragna. "The resonance phenomenon in an urban canyon has been shed to light for sonic boom, and its importance has been quantified."
The group performed numerical simulations drawing on equations from the field of fluid dynamics to predict the boom in different urban configurations. "This approach allows us to precisely account for the reflection of the boom on streets and facades of the buildings," Dragna said. "With these simulations, we were able to determine the ground pressure signals due to sonic boom propagation and reflection over the buildings and deduce noise levels. We can thus predict the noise annoyance felt by the population due to sonic booms."
The width of the streets and the height of the buildings made a difference. Narrower streets introduced complex propagation as the sound reflected off multiple surfaces – not necessarily making the boom louder, but prolonging the sound.
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