ACOUSTIC INSTALLATION EFFECTS ON AN AGILE HIGHLY SWEPT FLYING WING CONFIGURATION

Kurzfassung

Results of experimental investigations on engine noise shielding by an unmanned combat air vehicle (UCAV) are presented. The experiments were carried out in DNW-NWB acoustic wind tunnel using a newly developed laser-based pulsed sound source at the SACCON UCAV aircraft configuration. The results obtained demonstrate that the sharp-edged SACCON geometry leads to a sharply defined shadow region for wavelengths of the incident sound field which are large compared to the edges radius of curvature or thickness. In that case, sound wave diffraction through creeping waves does not play an important role, and higher levels of acoustic attenuation can be achieved. Furthermore, it was found that a positioning of the jet outlet further upstream of the aircraft’s trailing edge is beneficial, also leading to a higher acoustic attenuation. Noise generated at the inlet of the propulsion system was found to be much less attenuated compared to that generated at the outlet. This is a consequence of the position of the inlet on the symmetry plane of the model as well as to the relatively large radius of curvature of the aircraft wings leading edge. Inlet generated noise is registered, in the experiments, far downstream of the aircraft leading edge. This result emphasizes the potential necessity to achieve a clever integration of both inlet and outlet of the propulsion systems to maximize acoustic attenuation. A high noise attenuation at the outlet may potentially be cancelled out by a noisy and badly positioned inlet. A ranking of inlet vs. outlet noise could not, however, be done using the acquired database. This question remains open and will be the subject of future research. Numerical simulations of the experimental configuration were performed using DLR’s FMCAS code. The results were found to be in very good agreement with the experimental results, thus demonstrating the applicability of noise prediction methods to the problem of acoustic shielding.