Author: Swinbanks, Malcolm
to the Michigan WERZB Board, Case no. U-15899
NASA-Langley Wind-Turbine Research, 1980-1990
Following my letter to the MPSC, I returned to the UK over the Christmas break, which enabled me to access papers from conferences I had attended in the 1980’s. Specifically, NASA-Langley, probably the foremost aeroacoustic research organization in the world, carried out and published extensive research on wind-turbine noise, starting with their first computer predictive codes in 1980, and continuing through 1990.
During this period, NASA & NASA sub-contractors identified almost all of the specific issues relating to wind-turbine noise, that now are being re-learned the hard way, by bitter experience.
NASA calculated the sound levels generated by ideal turbine blades operating in clean airflow, and identified how inevitably, inflow conditions associated with atmospheric turbulence could result in unsteady blade loadings, thus increasing these sound levels. (1982 ). Moreover, they extended the work to consider the effect of a wind gradient, whereby the incident wind velocity varies with height across the face of the turbine, and showed that substantially higher noise levels can then be generated. (198, ).
Finally, they measured in practice the low-frequency threshold of hearing under laboratory conditions, for persons subjected to impulsive wind-turbine noise, and showed this could be almost 20dB lower (i.e. more sensitive) than the conventionally accepted noise threshold for less obtrusive sounds (1982 ).