The Aeroacoustics of Helicopter Rotors - European Research Projects

Abstract

Significant advances in understanding helicopter noise have been made through several recent major European dedicated rotor aeroacoustics research projects. The availability of the German Dutch Wind Tunnel (DNW) allowed research on relatively large main rotor models (up to 40% full-scale). The simultaneous application of blade-mounted absolute pressure sensors to probe into the aeroacoustic source mechanisms, of advanced acoustic-data acquisition systems for radiated noise, and of sophisticated flow-visualization/-measurement techniques (Laser Light Sheet, Laser Doppler Velocity) to study the interrelationship of rotor aerodynamics and blade dynamic response, has provided insight into the aeroacoustics or rotors. Towards controlling rotor noise, projects dealt with higher harmonic or individual blade control to affect vortex interaction. Much data served as benchmark information to advance theoretical rotor noise prediction for moderate tip speed conditions based on linearised potential flow methods or Euler methods combined with the "acoustic analogy approach", and for high tip speed conditions based on Computational Fluid Dynamics and Kirchhoff approaches. This paper discusses several major European helicopter aeroacoustics research projects (e.g. the EU-initiated HELINOISE and HELISHAPE projects, and the joint European-US HART project) to indicate recent relevant progress and how the findings provide guidance towards the ultimate objective - the quiet helicopter.