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Abstract-
An important hydroacoustic noise source from a fully-submerged noncavitating hydrofoil is the unsteady separated turbulent flow near its trailing edge. Here, hydroacoustic noise may be produced by boundary layer turbulence scattered from the foil's trailing edge, and by the periodic formation of vortices in the near-wake. Such vortex shedding may generate an energetic tone that rises above the broadband trailing-edge noise. This presentation describes results of an experimental effort to measure the major flow features in the near-wake of a high Reynolds number hydrofoil with trailing edge vortex shedding. The experiments were conducted at the US Navy's William B. Morgan Large Cavitation Channel with a two-dimensional hydrofoil (2.1 m chord, 3.0 m span) at chord-based Reynolds numbers from 0.5 to 60 million. Two trailing edge shapes producing differing strengths of vortex shedding were investigated. Measurements include time-averaged and unsteady surface pressures, and LDV and PIV derived velocity fields, and hydrofoil vibration. The dependence of the shedding strength on changes in Reynolds number and trailing edge geometry were investigated. The results indicate a correlation between the energy contained in the vortex shedding and the time-averaged shear of the boundary layers approaching the trailing prior to separation at the trailing edge bevel. These results have implications for both the passive and active control of the shedding strength. Additionally, a brief discussion of our upcoming high Reynolds number friction drag reduction experiment will be briefly discussed where we will examine the use of micro-bubble gas injection to reduce friction drag on submersed surfaces. [Sponsored by Code 333 of the Office of Naval Research, N00014-99-1-0341, N00014-99-1-0856, N00014-01-1-0880].
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