QUIET AEROFOILS OF THE NEXT GENERATION

Wind turbines and aircraft are well known to be noisy machines that limits their acceptability to people living close to their operation, such as wind farms and airports. This limitation of course has significant implications for the growth of the aerospace and renewable energy sectors, which is vital to the UK economy as a whole. Wind turbines and aircraft have common noise generation mechanisms, namely the interaction between the airfoil blades and wings with turbulent flow around it.

Conventional airfoils have straight leading and trailing edges, which according to recent research by the authors of this proposal, is the noisiest geometrical configuration. Significant noise reductions in airfoil noise have been obtained by introducing serrations (or undulations) into the trailing edge and leading edge geometries. In separate studies, introducing riblets onto the airfoil surface (very fine grooves) have also been shown to produce significant reductions in drag. It is reasonable to assume that airfoil drag and its noise radiation are connected, although this has never been formally investigated. An investigation into this association is one of the objectives of this work.

This project will seek to combine these three technologies into a single airfoil design for the simultaneous reduction of leading edge and trailing edge noise whilst preserving aerodynamic performance. This optimisation process will necessitate a fundamental understanding into their noise reductions mechanisms individually in order to ensure that their combined benefits are at least additive or may combine to be more effective than the sum of their benefits individually. The outcome of this work is a new generation of aerofoils with noise control at the heart of their design."

A reduction in aerofoil noise should have significant benefit in a variety of applications including wind turbines, aircraft engines and high-lift devices on aircraft wings, which in turn will make a significant impact to environmental noise. The proposed research will benefit the general public, particularly those in areas surrounding airports or wind farms, suffering from physical/mental health implications due to long-term exposure to environmental noise. The proposed work is intended to deliver a practically viable aerofoil design concept that can be exploited by the industrial partners to achieve significant reductions in noise levels.

Aviation noise represents a major obstacle to the future expansion of many existing airports and thus the growth in the capacity of the air transport system. Regulations in aviation noise are becoming increasingly strict. Aircraft manufactures are investing heavily to develop quieter aircraft. Although steep approach operations are becoming widespread to reduce noise emissions in urban airports, a technology breakthrough is urgently required in order to achieve significant noise reductions at source. At approach conditions, noise from the airframe, in particular from the high lift devices on the wings, is one of the dominant noise sources. Its attenuation is the primary objective of this proposal.

Another principal application of the proposed technology is wind turbines. The implication of wind turbine noise is highlighted in a recent white paper, "Wind Turbine Acoustic Noise" by Rogers, Manwell & Wright. They measured a striking increase in noise levels by as much as 13dB(A) under certain conditions when measured at 180 meters from the base of a 10kW wind turbine at Rockport, MA, US. They argued that a buffer zone of almost half a kilometre would be required to meet Massachusetts noise regulations. Clearly, any reduction in broadband noise levels, which this proposal aims to achieve, would alleviate such local planning problems, leading to increased acceptance of wind turbines near populated areas.

Vestas Technology UK have highlighted the importance of this proposal in their letters of support and have suggested interactive partnership throughout the lifetime of the project. The impact of the proposed research on the industrial partners will be maximised by delivering regular progress reports and organising annual full-day mini-conferences in which they will provide feedback. The impact of this work will be brought to the attention of the general public through the media.

The noise control technologies investigated in this work can also be found on owls who are well known for their quiet flight. The strong bio-inspired element to this work, and the potential benefit to the environment, will be of interest to science journalists, particularly in view of the sensitivity of wind turbine noise at the present time."