Acoustic Array Measurements of a 1:10.6 Scaled Airbus A340 Model

Abstract

Acoustic array measurements were carried out on a 1:10.6 scaled Airbus A340 model. Tests were done in both the open jet and a closed test section of the DNW-LLF wind tunnel. The purpose of these measurements was to investigate several noise reduction concepts for high-lift devices (slats and flaps) in landing configuration. The possibilities and limitations of arrays for the determination of quantitative results are discussed. Besides the identification of dominant noise source regions with conventional beamforming, local source spectra were determined using a power integration method. For the open jet results, the integration method was applied with and without the ’diagonal removal’ (DR) technique, in which the main diagonal of the cross-power matrix is discarded. It is shown that application of DR results in meaningful local spectra, whereas without DR the results are obscured by the influence of the main diagonal. On the other hand, by comparing integrated spectra with absolute sound levels on farfield microphones, it is shown that the application of DR, in combination with coherence loss, results in significantly reduced absolute levels. However, while the absolute sound levels can be too low, level differences between configurations can be accurately determined under certain conditions. From the closed test section array results, dominant source regions are identified as a function of frequency and angle-ofattack. These results are quantified by application of the integration method to several source areas on the wing. The local and overall effect of noise reduction devices is assessed. The effect of coherence loss on the absolute levels is investigated by varying the effective array size.