NATO STO

The state of the art of aircraft noise prediction and reduction has been largely focused on civil transport aircraft, while less effort has been invested in noise reduction of military aircraft. Noise reduction concepts can only partially be adopted from the civilian side, because of the largely different aircraft configurations in the military domain. Military aircraft noise is strongly influenced by engine noise characteristics. The integration of engine and airframe of military aircraft configurations is vastly different and provides significant potential for noise reduction, not available at typical tube-and-wing civil aircraft. For instance, conceptually, certain techniques, exploited to reduce the infra-red signature of combat aircraft may be modified to also reduce sound radiation. The following STO research activities in the past have contributed to building up the background to this RTG: -AVT-132 “Noise issues arising from the operation of gas turbine powered military air vehicles” -AVT-158 RSM addressed the noise from high-powered aircraft such as fighters, both in the community and on a carrier deck -AVT-233 “Aeroacoustics of engine installation of military air vehicles” established a validated computational tool basis to enable the prediction of acoustic installation effects of arbitrary configurations, achieved by numerical simulation (CAA=Computational Aeroacoustics). Starting from generic geometries (airfoil) and ending with a military transport configuration and the agile NATO type configuration SACCON the RTG was focused on validating these CAA codes in view of their capability to predict the acoustic shielding of engine noise. The source was deliberately kept highly generic (basically a monopole point source). -AVT-251 provided the overall aircraft design of an aerodynamically advanced and realistic configuration of SACCON type, called MULDICON; in that respect also AVT-161 and AVT-201 were instrumental in laying the foundations for AVT-251. -AVT-318 “Low Noise Aeroacoustic Design for Turbofan Powered NATO Air Vehicles,” focused on the MULDICON vehicle and added the jet noise source from the rectangular nozzle including the jet-trailing edge interaction arising from the highly integrated nozzle/airframe as well as a characterization of the inlet acoustic radiation. Experimental campaigns included a monopole point source generated inside the inlet duct and exhaust ducts. Considerable CFD and CAA studies were performed of the powered vehicle. An initial effort was performed to develop a noise reduction device, the Shielding Flap, that could be feasible to integrate with the MULDICON. Experimental and prediction studies were performed to understand the design parameters of the Shielding Flap and their acoustic impacts.