Sound sound-research techniques

Higher bypass ratios, chevrons, shape memory alloys, and improved aerodynamics are some of the advancing technologies that will help quiet aircraft, and thus help the environment.

Achieving London airports' QC2 noise level for the Trent 900 to power the A380 demanded very close liaison between Rolls-Royce and Airbus. It saw the development of an effectively spliceless inlet and fan case acoustic system. Rolls-Royce was responsible for the engineering of the fan case and Airbus for the inlet. A systems approach was used to ensure that the combined effect gave lower engine noise. Walsh says that may not sound significant “but to achieve a uniform surface that would successfully attenuate fan noise was quite a mechanical challenge. Imperfections in the acoustic treatment with any joints can disrupt the sound field, which at some frequencies may create added noise. We managed to achieve the very high degree of homogeneity required-a spliceless intake system.”

Attempting acoustic gains in the intake lip area also needs consideration with regard to any minus elements. “For example, we have to consider anti-icing/deicing aspects and we certainly must not degrade aerodynamic performance,” he said. A deep understanding of the physics of noise generation is essential, and the potential production solutions are being developed via extensive mathematical modeling and fan rig facility test work.