Experimental determination of the dominant noise mechanism of rotating rotors using hot-wire anemometer. (February 2021) - Zhang, Cui Qing
Highlights: The positions and values of maximum velocity fluctuation are acquired. The quantitative relationships between sound field and flow field are established. The dominant noise mechanism of rotating rotor is determined. Abstract: Aerodynamic noise restricts the development of wind turbines, however, the complex formation mechanism of aerodynamic noise needs to be explored for the successful realization of wind turbines in a wide range of applications. Herein, a two-dimensional hot-wire anemometer is used to capture the transient flow field at the rotor dominant sound source area from the open section of the wind tunnel. The influence of wind speed and tip speed ratio on velocity is systematically investigated by estimating the position and maximum value of velocity fluctuations. Moreover, the relationships between sound field and flow field are established in terms of frequency, position, and energy parameters. Finally, the noise generation mechanism is determined based on vortex and noise generation theories. The results reveal that the maximum velocity fluctuations are concentrated at 0.7–0.8C and 0.57–0.71 R in the chord and radial directions, respectively. One should note that the dominant sound source spectrum is consistent with the velocity fluctuation spectrum, exhibiting broadband characteristics. Furthermore, the sound source positions are consistent, but not coincident, with the positions of maximum velocity fluctuations. In addition, the sound source positions are closer to the blade tip and trailing edge in the radial and chord directions, respectively, than the maximum velocity fluctuation point. The deviations in radial and chord positions increase with increasing wind speed and tip speed ratio, whereas the deviations of maximum radial and chord position are found to be 1.4% and 36%, respectively. The sound pressure level and velocity fluctuation exhibit excellent consistency under different working conditions, such as different wind speeds and tip speed ratios. It can be concluded that the dominant noise is a broadband noise due to pressure fluctuations, which are induced by the interactions between turbulent flow and trailing edge. These results provide a baseline for the design and development of optimal blades and noise reduction.