Underwater flow noise measurements with a towed body

Flow-induced noise plays a crucial role for moving hydroacoustic sensor systems, such as hull mounted SONAR or acoustic streamer, because it limits their performance in particular at large speeds. The noise in the interior of a sensor system is generated from the surrounding turbulent boundary layer flow that excite or interact with the mechanical hull structure. Shape and physical properties of the hull determine therefore significantly the performance of a hydroacoustic sensor system. The sea is a noisy environment and deep water measurements require specialised measurement equipment. WTD71-FWG in collaboration with ATLAS Elektronik has developed a towed body measurement system for underwater flow noise measurements. Several research cruises with RV ELISABETH MANN BORGESE and the FLAME (Flow Noise Analysis and Measurement Equipment) towed body have been conducted in Sognefjord, Norway, between 2013 and 2015. The measurements were performed between 100 m and 200 m towing depth in a speed range from 4 kn to 12 kn. Results from underwater experiments on interior flow-induced noise beneath flat plate configurations with and without obstacle are presented. Array processing based on a wavenumber-frequency analysis is applied to separate disturbing exterior ship or ambient noise from interior noise.