Comparison of microphone array measurements in the closed test section of LSWT and ETW

Abstract

Aeroacoustic measurements in wind tunnels are a common tool in the determination of sound sources on scaled models. Measurements are performed worldwide in comparable wind tunnels. It is however not known to what degree a similar measurement in different wind tunnels will produce similar results. In this paper, therefore, a comparison of microphone array measurements using the very same aircraft half-model in the closed test section of two different wind tunnels with two different microphone arrays is made. For this, data from two measurement campaigns conducted in the LSWT in Bremen, Germany, and in the ETW in Cologne, Germany, were used. The comparisons are made by juxtaposing the two measurements in terms of source maps at individual frequencies and in terms of integrated spectra for different areas of the wing. Both comparison methods exhibit substantial agreement, but yet noticeable differences which are discussed afterward taking into account the model and model support, background noise, flow conditions, microphone array setup and post processing. Comparing and discussing the possible reasons yield insight about the repeatability of industrial microphone array measurements which will lead to a better interpretation of such experiments in the future.