Effectivity Assessment of Noise Reduction Technology by Means of Flight Tests

By means of flight tests DLR demonstrated the farfield noise reduction potential of selectednoise reduction technologies on airframe noise meant for aircraft retro-fitting. The majoroutcome of the flight tests was a landing gear noise reduction by about 3 dB and an overallairframe noise reduction of about 1.5 dB, which are both attributed to the beneficial effect ofthe add-on treatments1, 2.. The first data assessment was purely based on the analysis of singlemicrophone farfield noise data and thus the overall effect. The present paper emphasizes theanalysis of phased beamforming data acquired in order to identify the acoustic effectivity ofthe single devices. Furthermore, the use of numerical flow simulation in course of mesh fairingdesign is described. The simulation data is used to assess local flow properties downstream ofa porous fairing. Finally, the data can be used to apply even semi-empirical noise predictiontools more target oriented for design purposes.