Reducing aircraft noise during approach and landing
As an aircraft approaches the airport, high lift devices (HLDs) such as slats and flaps are used to minimise landing speeds, and landing gear (LG) is deployed. The noise from these airframe components presents a major challenge. “Reducing airframe noise generated by HLDs and LG has always been difficult,” explains INVENTOR project coordinator Eric Manoha from the French Aerospace Lab ONERA. “The design of these components has been optimised through decades of research to improve specific functionalities like aerodynamics, weight and safety. Any modification aiming at reducing noise must tentatively maintain these functionalities.”
Challenges to cutting aircraft noise
INVENTOR set out to identify possible new techniques to reduce noise from these components, while maintaining optimal functionality. The project’s aims were in line with the goals of Flightpath 2050 (the EU’s vision for aviation), which seeks to reduce perceived aircraft noise by 65 %. To achieve this, the project gathered European specialists from three aircraft / LG manufacturers, five research centres, six universities and two SMEs. This consortium, balanced between academy and industry, selected and assessed the most promising airframe noise reduction technologies (NRTs), using computational fluid dynamics and aerodynamic / acoustic experiments. “We followed two main approaches to achieving our aims,” explains Manoha. “The first was to add passive add-on technologies such as porous materials (flow-through fairings or surface liners) to existing components, to absorb noise while maintaining performance. These materials can also be used to mitigate against turbulence, the major generator of noise. We also looked at add-on active technologies such as local blowing.”
Component design to achieve quieter performance
The second approach taken by the project was to start earlier in the design process. The aim was to change the shape and design of certain elements to achieve quieter performance. “We did this with various components,” adds Manoha. “For example, we looked at several sub-elements of the LG, varying their section shape or spatial orientation with respect to the mean flow, without weight increase or modifications of the deployment ability, which remains the priority for safety.” In HLDs, the team focused on modelling new designs and smoother shapes of slat tracks, the mechanism used to deploy the slat at the leading edge of the wing, which is a source of noise during landing. Such innovative designs must also maintain the ability to safely deploy the slat. “These examples underline how non-acoustic considerations might restrict the airframer’s capacity for radical redesign,” says Manoha.
Further noise reduction of landing gear possible
Through computer modelling and testing, the INVENTOR project was nonetheless able to demonstrate how noise reduction could be achieved through different component design approaches. The project worked closely with industry throughout, and very much sought to deliver concepts that had a chance of eventually making it to market. “Taken individually, the noise reductions are modest and in line with our initial realistic objectives,” says Manoha. “However, combining several of these technologies together with next generation of quieter engines could help to significantly reduce noise pollution from aircraft at landing.” If successfully implemented, these components could bring benefits to passengers and citizens who live near airports and help boost Europe’s aerospace industry in developing next-generation airframes. Next steps include better understanding the physics involved, optimising designs and testing on aircraft.
Keywords
INVENTOR, aircraft, airframe, aviation, noise, aerospace, Flightpath 2050
