Turbulence induced self-noise on cylinders in low velocity flow

Abstract

Nominally stationary acoustic sensors, e.g., buoy suspended or bottom anchored, are subject to various environmental flows. These flows in turn generate turbulence along the surface of acoustic enclosures that give rise to self-noise. A continuous-flow water tunnel replicates at-sea flows for evaluation of acoustic enclosures for such self-noise. In preparation for the tunnel experiments, direct numerical simulations of hydrodynamic flow around the acoustic sensor housing have been performed, and show turbulence along the housing surface. Time-space analysis of pressure variation along the surface of the housing shows significant acoustic-like surface interaction at low frequencies, even at very low mean flow velocity. The broad frequency content of the turbulence is due to intermittently generated, irregular, coherent vortex structures that separate from the surface of the housing and advect downstream. These structures drive rapid surface pressure transients that propagate within the housing to the acoustic sensors as noise. The potential for noise reduction using foil shaped housing is explored. This research is supported by 6.2 NRL base program sponsored by the Office of Naval Research. Distribution Statement A: Approved for public release. Distribution unlimited.