Suppression of Hydroacoustic Flow Noise using a Self-Aligning Eppler Foil

Flow-induced self-noise remains a continuing challenge for the performance of sensors in dynamic fluid environments, for example wind noise on microphones or current-induced turbulence on ocean pressure sensors. We present here experimental results from synchronous measurements of 1) time-resolved particle image velocimetry (TR-PIV) flow fields over an Eppler 863 fairing, 2) acoustic data from a hydrophone embedded within the fairing, and 3) restoring moment forces on the fairing when positioned at a non-zero angle-of-attack. Self-noise levels were then compared with synchronized TR-PIV and hydrophone measurements over a similarly scaled, traditional cylinder enclosure. Experiments were performed in the US Naval Research Laboratory’s unique open-loop HydroAcoustic Flow Channel, in which flow is driven by the static head pressure from an adjacent 38,000 gallon holding tank resulting in an extremely low noise floor compared to traditional pump-driven flow channels. We report mean and time-resolved turbulent boundary layer flow fields, power spectra of the pressure field propagating to the embedded hydrophone, and time histories of torque forces for a freely rotating fairing. Experimental data is also used to validate and compare with our previously reported Large Eddy Simulation (LES) numerical data, which demonstrated a frequency-dependent, but significant reduction in flow noise for the fairing model.