“Urban canyons” extend sonic booms into cities

Twenty years after the withdrawal of Concorde, several industrial and research projects want to make supersonic flight a reality again. However, supersonic aircraft produce sonic booms loud enough to warrant noise concerns and regulations, limiting their use on land.

In The Journal of the Acoustical Society of Americaresearchers from the University of Lyon conducted simulations comparing sonic booms reflect differently on a single building, two neighboring buildings and several buildings spaced at regular intervals.

“This article is the first study to deal with the spread of the boom in a urban environment“, said co-author Didier Dragna. “The phenomenon of resonance in an urban canyon has been unearthed for the sonic boom, and its importance has been quantified.

The Federal Aviation Administration currently prohibits commercial aircraft to travel faster than Mach 1 on land and from a certain distance offshore where a boom can reach US shores. Recent efforts have sought to make low-boom supersonic aircraft, but noise problems from sonic booms can become more pronounced in cities, where buildings form canyons that distort the booms.

The band played numerical simulations draw on equations from the field of fluid dynamics to predict the boom in different urban configurations.

“This approach allows us to accurately capture the reflection of the boom on streets and building facades,” Dragna said. “Thanks to these simulations, we were able to determine the ground pressure signals due to supersonic detonation propagation and reflection on buildings and deduce noise levels. We can thus predict the noise annoyance felt by the population due to sonic booms.”

The researchers found that the wider the streets are in relation to the height of the buildings, the less the ramps are affected by the presence of several buildings.

Narrower streets introduce more complex boom propagation through multiple reflections on building facades. Although they do not affect boom volume, they tend to prolong ground-level pressure signals in urban canyons by increasing resonance between buildings.

Dragna said their research underscores the importance of the shape of cities to the characteristics of sonic booms at ground level. The group aims to dig deeper into the phenomenon by examining the typical configurations of the city.

The article is titled “Sonic Boom Reflection on Isolated Building and Multiple Buildings”.