Microphone-Array Measurements on a Scaled Model in ETW at Real-Flight Reynolds Numbers

This paper presents an experimental investigation of small-scale model airframe noise at various Reynolds numbers up to the real-flight case. The study consists of data acquired with a microphone array in the European Transonic Windtunnel (ETW). The advantage of the ETW is to enable testing simultaneously at cryogenic temperatures and increased pressure levels, which extends the range of achievable Reynolds numbers up to those pertaining to full-scale flight conditions. At the German Aerospace Center (DLR), the microphone-array measurement technique has been further developed to perform measurements under combined cryogenic and pressurized conditions. For this purpose, a microphone-array consisting of 96 microphones was designed and constructed. In this paper, aeroacoustic results are presented for various Reynolds numbers up to the real-flight case on an Airbus K3DY half-model of scale 1:13.6. The results showed significant Reynolds number and Mach number dependency for various sources. Of particular note are various dominant sources appearing on the flap at real-flight Reynolds numbers. To the authors knowledge, this is the first time that airframe noise data for a small-scale model have been acquired at real-flight Reynolds numbers.