Phased microphone arrays have become a well-established tool for performing aeroacoustic measurements in wind tunnels (both open-jet and closed-section), flying aircraft, and engine test beds. This paper provides a review of the most wellknown and state-of-the-art acoustic imaging methods and recommendations on when to use them. Several exemplary results showing the performance of most methods in aeroacoustic applications are included. This manuscript provides a general introduction to aeroacoustic measurements for non-experienced microphone-array users as well as a broad overview for general aeroacoustic experts.

No abstract

In this work, various microphone phased array data processing techniques are applied to two existing datasets from aeroacoustic wind tunnel tests. The first of these is from a large closed-wall facility, DLR's Kryo-Kanal Köln (DNW-KKK), and is a measurement of the high-lift noise of a semispan model. The second is from a small-scale open-jet facility, the NASA Langley Quiet Flow Facility (QFF), and is a measurement of a clean airfoil selfnoise. The data had been made publicly available in 2015, and were analyzed by several research groups using multiple analysis techniques. This procedure allows the assessment of the variability of individual methods across various organizational implementations, as well as the variability of results produced by different array analysis methods. This paper summarizes the results presented at panel sessions held at AIAA conferences in 2015 and 2016. Results show that with appropriate handling of background noise, all advanced methods can identify dominant acoustic sources for a broad range of frequencies. Lowerlevel sources may be masked or underpredicted. Integrated levels are more robust and in closer agreement between methods than narrowband maps for individual frequencies. Overall there is no obvious best method, though multiple methods may be used to bound expected behavior.

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.Nomenclature * Research Associate, German Aerospace Center. Associated member AIAA.

The present paper addresses the development, qualification trials and application of some non-intrusive measurement techniques suitable for operation in industry-scale, pressurised cryogenic wind tunnels. The application of cryogenic Temperature-Sensitive Paint (cryoTSP) as a tool for transition detection is described as well as the implementation of the Image Pattern Correlation Technique (IPCT) and the Backward Oriented Schlieren method (BOS) in the European Transonic Windtunnel (ETW). Progress on the development of cryogenic Pressure-Sensitive Paint (cryoPSP) is shown, and considerations for the establishment of a Particle Image Velocimetry system suited for low temperatures (cryoPIV) are presented. Furthermore, the state of adaptation of the microphone array technique (MAT) to industry-scale, cryogenic wind tunnels is described.