Low-Frequency Noise Propagation from a Small Wind Turbine Tower

A major barrier to the acceptance of small wind turbines is that they are perceived to be noisy particularly when mounted on monopole towers rather than traditional guy-wired ones. Noise emission from a 2.4 kW downwind turbine due to its 10.2 m monopole tower was investigated. Tower vibration was measured using 24 accelerometers. A finite-element tower model combined with simple assumptions for the turbine and wind loads allowed the noise to be obtained from solution of the wave equation. The measured vibration levels were matched to the tower model amplitudes. Sound pressure level produced by the fluid–structure interaction reached 30 dB at about 11 m from the tower and decreased to 5 dB 1 km away. Propagation switched from cylindrical to hemispherical when the distance was about 200 times larger than the tower height.