Airplane noise is more than just a momentary distraction — it can be downright bad for health. According to previous research, the sounds of planes flying overhead can ruin sleep quality for people who live near airports. Another study found that people exposed to airplane noise at night are more likely to suffer heart failure. So, is it possible for jets to one day have silent engines? This tantalizing prospect, believe it or not, is now one step closer to reality, thanks to innovative research conducted by a team of engineers at the University of Bristol in the United Kingdom.
Their findings, recently published in the Journal of Fluid Mechanics, shed new light on the noise generated by an innovative type of aircraft engine known as a boundary layer ingesting (BLI) ducted fan.
So, what exactly is a BLI ducted fan, and why is it generating so much excitement in the aviation industry? To put it simply, these engines are a bit like the ones you’d find on a typical modern airliner, but with a clever twist. Instead of being mounted under the wings, they are partially embedded into the main body of the aircraft. This unique configuration allows them to “ingest” air not just from the front but also from the surface of the plane itself. As a result, the engines don’t have to work as hard to propel the aircraft forward, leading to significant fuel savings.
But while BLI ducted fans promise to revolutionize the way we fly, there’s a catch: noise. Until now, very little was known about how these engines actually generate and propagate sound, especially when they are mounted on curved surfaces like the fuselage of an aircraft. This is where the Bristol team, led by researcher Feroz Ahmed and Professor Mahdi Azarpeyvand, comes in.
Using the state-of-the-art facilities at the University’s National Aeroacoustic Wind Tunnel, the researchers were able to pinpoint the various sources of noise in a BLI ducted fan setup. They discovered that the noise pattern changes depending on how much thrust the fan is producing. At high thrust levels, the noise is similar to what you’d expect from a conventional, unducted fan. But when the fan is producing less thrust, something interesting happens: the duct itself starts to contribute more to the overall noise.
To better understand these phenomena, it’s helpful to think of a BLI ducted fan as a bit like a high-tech hairdryer. When you turn a hairdryer on full blast, most of the noise comes from the fan inside. But if you turn it down to a lower setting, you might start to notice a different kind of sound, perhaps a whistling or whooshing noise coming from the duct or nozzle. In a similar way, the noise from a BLI ducted fan is a complex interplay between the fan itself, the duct that surrounds it, and the air flowing over the curved surface of the airframe.
The Bristol team’s research is a crucial first step in understanding and ultimately mitigating the noise generated by these innovative engines. By breaking down the various noise sources and studying how they change under different operating conditions, the researchers are paving the way for quieter, more efficient aircraft designs.
But why is this so important? For one thing, noise pollution is a major concern for communities living near airports. Quieter planes would not only improve the quality of life for these residents but also potentially allow for more flights to operate during noise-sensitive hours, such as early mornings or late evenings. Moreover, reducing noise is a key hurdle in getting new aircraft designs certified by regulatory agencies.
There are also exciting implications for the future of urban air mobility. Many companies are currently developing small, electric vertical take-off and landing (eVTOL) aircraft for use as aerial taxis or personal vehicles. These designs often rely on ducted fans for propulsion, and minimizing noise will be critical for their acceptance and widespread adoption in cities.
The Bristol team’s work is already garnering attention from major players in the aviation industry. Projects like the Bell X-22A, Embraer X, Airbus E-fan, Lilium Jet, Green Jet, and Hybrid Air Vehicle are all exploring the use of embedded ducted fans for next-generation aircraft. By providing a clearer understanding of the noise challenges involved, the research could help guide the design and development of these futuristic planes.
Source: https://studyfinds.org/silent-airplanes-new-aviation-tech/
