A Temporal Wind Turbine Model for Low-Frequency Noise

In this paper, low-frequency noise and its generation are investigated using an in-house numerical model named HAWC2-Noise. This code simulates the aerodynamic behavior of a wind turbine and it is coupled with aerodynamic noise models. In particular, it can model the atmospheric turbulence impacting the turbine rotor, which may have an impact on the wind turbine loads and more importantly in the present context, on the acoustic reponse of the blades to this varying loading in the low frequency range. Furthermore, the loading due to the passage of the blades in the tower's wake, which is known to be a major source of low-frequency noise for downwind turbine, can also be simulated. In order to compute the acoustic response of the blades to the above loadings, the formulation 1A by Farassat is implemented into the code. The influence of the level of detail for the loading model on the acoustic response is investigated. It appears that a more detailed model for the airfoil radiating surface yields a more frequency-rich acoustic response. The above noise generation mechanisms (wake tower deficit and atmospheric turbulence) are investigated in the context of real MW-size wind turbines. Results are compared with an existing model describing the turbine loading as a uniform rotor disk and the noise generation for each individual blades (Viterna's model). The present model is further used to perform a parametric study of the main factors influencing these low-frequency noise mechanisms.