Researchers carry out tests in bid to develop quiet appliances

The immediate applications will be for the next generation of vacuum cleaners and fans, but the research also has the potential to improve the development of silent helicopter intakes, industrial refrigerators, jet engines and wind turbines.

The first of two planned projects focuses on the aeroacoustics of cyclone separators — complex 3D flows that swirl about a central column of fluid in line with the axis of rotation.

‘The core itself becomes unstable beyond a certain velocity of operation and when this happens the core starts precessing — the thing starts wobbling — and the frequency at which this wobbles is the frequency of the noise,’ said Dr Anurag Agarwal, project lead and lecturer in aeroacoustics at Cambridge. ’This is a large source of noise and we’d like to understand the physics of this.’

Some of the planned experiments will involve building a simplified model of a cyclone separator in water, then using dye injectors within a Perspex tunnel to gather data.

‘Then we’ll do some mathematical modelling of the instability and find ways of suppressing the noise,’ added Agarwal.

As well as vacuum cleaners, the research has a wide range of applications from silent helicopter intakes to the Ranque-Hilsch vortex tubes used for industrial refrigeration.

For the second project, Agarwal’s team will work on developing a completely silent fan, based on Dyson’s existing Air Multiplier model.

‘It’s already a good design, but there are several sources of noise in the fan — there’s an impeller, which is like a compressor, which produces a bit of noise. Then from the impeller, air comes out and it interacts with outlet guide vents — that’s also a source of noise.

‘We want to to come up with the ultimate low-noise design,’ said Agarwal.

In a separate project, the team is working with Mitsubishi Heavy Industries to look at ways of reducing noise from wind turbines. The team is also working with Rolls-Royce on an EPSRC-funded project to reduce the noise of jet engines in aircraft.

Agarwal said the key element in all the projects will be to reduce noise but without compromising performance or power.