Unsteady Surface Pressure Characteristics on Helicopter Blades: A Key to the Physics of Rotor Noise

Abstract

There are a number of approaches to predict helicopter rotor noise. The most common of these is the "Acoustic Analogy Approach" where (aerodynamic) source characteristics at and near the rotor blade are used as input into appropriate acoustic codes. Aerodynamic source characteristics may be determined by means of certain computational schemes, such as linearized potential flow methods (lifting line, lifting surface, unsteady panel methods) and full potential or Euler methods to yield the unsteady pressures on the blade surface or the perturbation velocity near the blade. Acoustic codes, such as the -meanwhile "classical"/Ffowcs Williams and Hawkings formulation may then be employed to compute the radiated acoustics. The key to validating the various aerodynamic and acoustic codes is the availability of - experimentally determined- high quality aerodynamic and acoustic data. An appropriate benchmark experimental program (within the framework of the European Community initiated HELINOISE project) has recently been conducted to provide the needed information. This paper discusses the usage of the now available data.