Acoustic characteristics of a Darrieus vertical-axis hydrokinetic rotor under loading conditions

초록

In the present study, the hydrodynamic and acoustic characteristics of a three-bladed lift-type hydrokinetic rotor were numerically investigated. The computational fluid dynamics (CFD) simulations were based on the unsteady Reynolds-averaged Navier-Stokes (URANS) governing equations in combination with the Ffowcs-Williams and Hawkings (FW-H) acoustic model, to resolve the flow and acoustic fields. The six degrees of freedom (SDOF) model was employed to correlate the instantaneous rotational speed of the rotor to external loads. The results show that the rotor achieves a maximum power coefficient of 0.32 at a tip speed ratio of 1.66. In the regions above and below the rotor, sound pressure exhibits periodicity at the blade-passing frequency, whereas in the streamwise direction, peak sound pressure levels are observed primarily at the rotational frequency. Additional low-frequency components are also identified, and their possible association with tip-vortex shedding and blade-wake interactions is discussed. Directivity patterns of overall sound pressure level indicate directional noise radiation, with both magnitude and dominant emission direction varying with operating condition. Overall sound pressure level declines with increasing streamwise distance from the rotor. Reducing external loads leads to enhancement of peak sound pressure levels in vertical directions and increased broadband noise in the streamwise direction. Overall, this study applies an integrated URANS/FW-H/SDOF numerical scheme to investigate the hydroacoustic characteristics of Darrieus rotors under load-dependent operating conditions.

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