Turning the volume down on environmental noise pollution

As Australia inches closer towards reaching its 2050 net-zero acoustic requirements, a team at UNSW are leading the way forward with their research into flow-induced noise and its impacts on public health. Focusing on the way in which airflow creates sound, Professor Con Doolan and Associate Professor Danielle Moreau of the School of Mechanical and Manufacturing Engineering have developed new technology to help reduce the audible sound created by aircrafts, drones, propellers and wind turbines – making places and spaces healthier for all. “There are so many different applications associated to what we do,” says Prof. Doolan. “At the end of the day, these issues touch so many people’s lives.”

The UNSW Flow Noise Facility Acoustic Tunnel. Credit: UNSW.

Working across this highly specialised field, Prof. Doolan and A/Prof. Moreau are tackling problems that sit between the worlds of acoustics and aerospace. “We take a wind tunnel for example and measure noise and turbulence inside that wind tunnel, which is a really challenging thing to do – it’s like being across two disciplines,” explains Prof. Doolan.

Their expertise is bolstered by the world-class flow noise facilities on campus, including the UNSW anechoic wind tunnel, the large aerodynamic wind tunnel, rotor noise test rig, Archer supersonic wind tunnel and advances flow and noise measurement systems. “Our wind tunnel is one of the only facilities in the country that can look at the problems we’re trying to solve,” adds A/Prof. Moreau.

As foundational work, their research provides invaluable insights and core knowledge to those who can then turn this into tangible outcomes. “We work on assisting design, which gives engineers the tools and understanding to do what they need to do,” says Prof. Doolan.

“We’ve worked with everyone from Resmed to Cochlear and have given them methods and advice, which influences their designs.”

Noise from above

Audible sound from wind turbines, drones and airplanes can cause significant problems for humans and animals alike, making this an urgent public health issue that needs solving. “This type of noise raises stress levels and can create hypertension as well as long-term health issues, learning difficulties in children, sleep disturbances and more,” explains Prof. Doolan. “In Europe, they’ve done this huge study looking at the burden of disease created by noise and over the whole population of the EU they have this shocking figure of roughly a million years of life lost due to accelerated aging caused by noise.”

To meet net zero requirements by 2050, aircraft will have to work on new propulsion systems, ensuring the significant noise created upon take-off and landing is reduced as much as possible. This will see the team continue their work across boundary layer ingestion, which involves immersing an engine into the airframe itself. “It looks really sleek, but it creates all this noise – and this has to be controlled,” adds Prof. Doolan.

Associate Professor Danielle Moreau on-campus at UNSW standing next to a wind tunnel fan. Credit: UNSW.

Rowena Dixon member of The Flow Noise Group, which is dedicated to the study of flow-induced noise and its control, performing noise measurements of a wing in the wind tunnel. Credit: UNSW.

Changing the shape of sound

Much of the research conducted by Prof. Doolan and A/Prof. Moreau during the last few years includes the serration of wings of air foils, as geometrical changes to the shape of a wind turbine blade changes the way they make sound. “We’ve tested a whole multitude of different shapes and have come up with some nice designs,” says Prof. Doolan.

“We’ve even worked for Gold Wind, the biggest wind turbine company in the world, and now we’re looking at putting serrations on drone propellers to try to reduce their noise as well.”

This work will be particularly impactful as the use of drones becomes more commonplace in everyday life. “They keep saying there will be drones flying everywhere in the future, so if that’s the case, there’s will be a lot of noise that comes from this, so we’re working on quietening those, which would lead to sustainable aviation,” adds Prof. Doolan.

Traveling sound below the surface

While Prof. Doolan and A/Prof. Moreau work on solutions for air-related noise, Professor Nicole Kessissoglou is looking the other way, with her research focusing on noise pollution underwater. “The topic of noise is something we have in common – even if it’s across different applications, topics and partners,” she says. “I investigate acoustic coatings applied to the wetted surface of marine vessels, with the dual purpose of absorbing incoming sound and reducing outgoing sound within the marine environment from onboard machinery.”

Through a fundamental modelling perspective and lens, Prof. Kessissoglou’s work looks at using less material or thin coatings on underwater vessels or structures to help absorb the low frequency sound. As underwater noise is low-frequency, long wavelength and can propagate for hundreds of kilometres, this is particularly important. “Low frequencies have long wave lengths and those need a lot of material to absorb the sound, so we look at the geometry, shape and material of the inclusion.”

What’s more, the impact of this noise on marine life can be significant. “I had read an article recently about 77 healthy whales that had beached themselves, and it was all because they were exposed to underwater noise, which damaged their inner ear,” explains Prof. Kessissoglou. “Within the marine environment, our noise can cause damage by affecting navigation and causing sickness.” This noise is often caused by human endeavours within oil and gas exploration, offshore wind turbines, blasting and defence activities.

As their research continues, all three professors are focused on taking a multi-solution approach to solving the issues at hand. “It’s not one design or solution – reducing noise requires multiple solutions because there are so many factors that each contribute to a quiet product,” says A/Prof. Moreau.

“All the problems we set out to investigate are challenging – from a scientific point of view to an experimental point of view. We need to understand how the noise is being generated and come up with innovative ways to try and control it.”

Hero image: Associate Professor Danielle Moreau with UNSW students inspecting a rotor rig to study noise generation. Image credit: UNSW.