Acoustic Radiation from an Integrated High Aspect Ratio Rectangular Nozzle with Co-Flow

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This contribution presents an experimental investigation of the acoustic radiation from an integrated high aspect ratio rectangular nozzle with co-flow. Experiments are carried out on the DLR-F24 Muldicon UCAV model in the acoustic test section of the DNW-NWB wind tunnel to provide a database on jet acoustics of a realistic UCAV configuration. The aim of these measurements is to identify relevant scaling parameters and provide a better understanding of the mechanism of sound production for such configurations. In co-flow conditions and for the fly-over and rear-arc radiation directions, the main driver to the acoustic production is identified to be a flow-edge scattering mechanism. Even in the rear-arc direction, classical jet mixing noise only defines the mid- to high-frequency range of the spectrum. This observation suggests, that for the type of nozzle and nozzle installation considered herein, an effective noise mitigation strategy should be aiming at reducing the edge noise production. Similar observations are made for the static conditions case. The occurrence of quasi-tonal source components is discussed with respect to a possible acoustic feedback mechanism. Extensive source directivity and distribution data are provided which lend further support to the source mechanisms identified through the scaling analysis. These results also emphasize the impact of sound wave diffraction and scattering by the vehicle's airframe on the far-field acoustic radiation characteristics.