Radiated sound from a cross-flow turbine with pitching hydrofoils

An underwater drone turbine generator unit is currently under development. The turbine consists of three cross-flow pitching foils. While understanding single turbine lift, thrust, and torque performance in a reverberant tank with a six-component load cell, an opportunity arose to quantify its radiated sound performance since such information may have an environmental impact on marine mammals and fish. Unsteady lift and drag on a non-cavitating hydrofoil, quantified by the time-dependent load cell response, results in dipole sound. This radiated sound power within the reverberant tank also results in a uniform distribution acoustic pressure that can be measured with hydrophones. Given the tank properties such as volume and frequency dependent reverberation time constants, the radiated sound can be quantified. The low frequency sound power is therefore quantified using the load cell and the high frequency sound power by averaging hydrophone levels. The sound power for the two frequency ranges with excellent overlap are shown for a single turbine with a span of 900 mm and diameter of 450 mm operating at 107 rpm.