Abstract
A novel aerodynamic-whistle-based ultrasonic tone generator is proposed that has the potential to serve as a bat deterrent when installed on wind turbine rotor blades. The device uses blade-relative flow to excite resonance in cavities that are geometrically tailored to generate tones at the desired ultrasonic frequencies. A comprehensive experimental and numerical study is presented wherein two such deterrent designs are investigated. Experiments are performed in an anechoic wind tunnel where the deterrents are mounted on a blade section with the NACA 0012 profile. Measurements show that the deterrents produce the desired tonal spectrum when the tunnel flow speed exceeds a threshold value. There is also a maximum flow speed above which the deterrents do not generate tones. Variations with flow speed and blade angle of attack are investigated. Acoustic beamforming is used for source localization with partial success. The compressible unsteady Reynolds-averaged Navier-Stokes equations are solved with the SST ?−? turbulence model to simulate the aeroacoustics of the deterrents. Two-dimensional simulations capture the tonal frequencies and the trends with flow speed and blade angle of attack observed in the experiments. Three-dimensional simulations are performed with span-periodic boundaries for two deterrent configurations – one with one resonator modeled and another with two resonators modeled. The flow unsteadiness is higher in the two-resonator configuration; however, the unsteady pressures in the two resonators are nearly out of phase. The Ffowcs Williams-Hawkings acoustic analogy is used to compute far-field acoustics. The simulations capture the tonal sound pressure levels at the fundamental frequency and the second harmonic.