Investigating Noise Shielding by Unconventional Aircraft Configurations

Abstract

First experimental results on investigations of the shielding characteristics of three unconventional aircraft configurations are presented. DLR's Low Noise Aircraft, a scaled-down version of NASA's Hybrid Wing Body configuration and DLR's F17E Unmanned Combat Air Vehicle configuration are all investigated in the acoustic plenum of the DNW-NWB wind tunnel at DLR in Braunschweig. Using a laser-based non- intrusive impulsive point source, various effective engine placements were investigated for selected model settings. Shielding factors are calculated from in-flow measurements made over a large spatial extent in the fly-over plane. For the present application of the laser-based point source, a custom optical setup was developed to achieve a focal length large enough for its use in the DNW-NWB. In this report emphasis is, therefore, put on a presentation of the optical design and on the characterization of the resulting sound surce. The shielding results presented herein provide a first look into the acquired database. Future work will be focussed on a finer analysis of the acquired database as well as on the realization of companion numerical simulations aimed at the validation of in-house simulation tools. The work presented herein will also serve as a basis for the elaboration of guidelines for the design of low-noise UCAV configurations.