Ten Years of Cooperative Helicopter Aeroacoustics Research in the DNW.

Abstract

Both the main rotor and the tail rotor of a helicopter generate noise as individual sources. They also interact aerodynamically, causing "interaction noise". Since there is no uniform inflow into the rotor, an individual rotor blade is subjected to widely differing flow conditions. To make the helicopter an environmentally acceptable aircraft, it must be quiet. It is, therfore, the task of the scientist and the research engineer to further the understanding of the mechanisms of noise generation of helicopter rotor, to develop means of controlling these mechanisms towards less noise generation, and to provide the helicopter manufacturer and the operator with guidance on how to build and fly an acoustically "non-intrusive" aircraft. The German Dutch Wind Tunnel (DNW) meets most of these stringent qualifications for conducting high quality aeroacoustic rotor system tests. In this paper some of the more outstanding research projects that were conducted in the DNW by the staffs of the DLR, of the NASA-Langley Research Center and of the US-Army, frequently cooperative and within the framework of "Memoranda of Understanding" or of "Letters of Agreement" are discussed.