A discussion of wind turbine interaction and stall contributions to wind farm noise

• Rotor–wake interaction plays a role in wind farm noise.
• More wake data needs to be collected.
• Dynamic stall noise needs to be characterised.

Wind farms have recently been reported to produce a noise signature that is described as possessing a “thumping” quality. Measurements of these signatures are limited and their effects are debated but their effect on public opinion and complaints make them a concern for researchers in this field. Proposed reasons for these noise signatures include amplitude modulation, interference patterns and wake–rotor interaction. This paper discusses these effects and concludes that wake–rotor interaction plays a role by causing variations in turbulent-inflow noise and dynamic stall. The current state of research into stall noise and wind turbine wake structure is also reviewed and it is concluded that the available information and collected data on wind turbine wake are insufficient to determine how strong this role is. More information on the velocity and turbulence fields in the wake of horizontal-axis wind turbines as well as a characterisation of the noise produced by an airfoil experiencing dynamic stall is required in order to make a full assessment of rotor–wake contributions to wind farm noise.