Aeroacoustic Measurements of a Scaled Half Model at High Reynolds Numbers

Abstract

The measurement of airframe noise on small-scale models is a well-known and common practice in conventional wind tunnels. Because conventional wind tunnels cannot generally achieve full-scale Reynolds numbers, measurements during the development process of modern aircraft are performed in cryogenic and/or pressurized wind tunnels that are capable of higher-Reynolds-number flows. Thus, the characteristics of the moving fluid are better adapted to the scale model. At the Göttingen Institute of Aerodynamics and Flow Technology of DLR, German Aerospace Center, the microphone-array measurement technique was further developed to perform measurements in a cryogenic wind tunnel at temperatures down to 100 K. A microphone array consisting of 144 microphones was designed and constructed for this purpose. In this paper, acoustic-array measurements performed in a cryogenic wind tunnel are described for various Reynolds numbers using a 9.24% Dornier 728 half-model. Our results showed a significant Reynolds-number dependency of the measured equivalent sound power for various sources.