Effectivity Assessment of Noise Reduction Technology by Means of Flight Tests

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