Lift-off for quieter planes

Rolls-Royce is to lead a project to develop technology for manipulating jet engine exhaust, to reduce aircraft noise at take-off and landing.

The firm will design and test an adaptive noise-control system as part of the £3.3m Aircraft Noise Disturbance Alleviation by Novel Technology (Andante) project.

The programme, which includes Airbus UK, Messier-Dowty, Camcon, Qinetiq and Southampton and Cambridge universities, aims to develop noise-reduction technologies for aircraft engine jets and fans, and landing gear.

The technologies will contribute to meeting the ACARE (Advisory Council for Aeronautics Research in Europe) target of a 10dB noise reduction by 2020, and to alleviating noise around airports, said Dr Nick Humphreys, the project’s co-ordinator at Rolls-Royce.

‘The idea is to target the main sources of noise with novel devices, and in conjunction with previous programmes, to create noise reduction in line with the ACARE targets.’

Among other concepts being considered is binary actuation technology, developed by Cambridge firm Camcon, to alter the flow characteristics of the jet exhaust.

According to Camcon, the majority of aircraft noise results from the speed of the exhaust gas being much greater than the speed of the aircraft through the air. The exhaust penetrates the surrounding air without mixing with the local atmosphere, creating vortices behind the engine, which materialise as a thunderous roar.

Camcon’s binary actuation technology could actively modulate the exhaust gases and mix them with the air, to reduce these vortices.The company’s actuators consist of a sprung armature held in place by two magnets.

A short electrical pulse disrupts the magnetic field, causing the armature to switch from one position to another, opening or closing the valve. Unlike with alternative electromagnetic valve control technologies, the natural position for the system is either open or closed, so it consumes very little power.

Ian Anderson, chief operating officer at Camcon, said the valves operate at very high speeds, and should ultimately be able to reach frequencies of up to 10,000Hz.

‘They are also very fast reacting. So unlike [conventional] solenoid technology where you use a lot of energy to start the process of movement from one state to another, our technology is such that it catapults itself from one stage to another, so it starts very fast,’ he said.

The technology also lands ‘softly’ when switching between one position and the other, reducing wear and tear and prolonging its operational life.

Camcon is running a DTI-backed research project at its Cambridge site into the use of its technology in exhaust noise reduction. In experiments with the Berlin Technical University the company has also used its valves to reduce the high-pitched noise emitted at the front of the engine by its jet blades.

‘We are addressing the roar from the rear and the scream from the front,’ said Anderson.

As part of the 30-month Andante project the team will test the valves on a model scale rig.

The project also aims to design concepts for low-pressure gas turbine systems with low-speed fans, and low-noise landing gear. Each of the technologies will be tested at Qinetiq’s aero-acoustic measurement chamber at Farnborough.

Half the project’s cost will be met by the DTI, with the remainder from the industrial partners.