S65 Atmospheric Pressure Fluctuations in Natural and Wind-Farm Boundary Layers

Sunday, 7 January 2018
Exhibit Hall 5 (ACC) (Austin, Texas)
Aaron J. Mehner, Valparaiso University, Valparaiso, IN; and D. A. Rajewski, S. Purdy, and E. S. Takle

Atmospheric pressure fluctuations redistribute turbulent kinetic energy within the atmospheric boundary layer at sub-cm scales. These perturbations create a pressure pumping at the surface which influences biological soil and plant processes. Pressure fluctuations on larger scales affect wind turbine efficiency within large wind farms. Wind turbines also create pressure perturbations that could impact crops or reduce the power efficiency of nearby turbines. Measurements of pressure fluctuations taken around wind turbines are limited; however, up to 10-Pa of pressure fluctuation around the turbine tower base have been reported from numerical simulations. This study examines spatial and temporal variations of pressure fluctuations in both natural and wind-farm boundary layers in central Iowa. Two nanobarometers measure microscale resolution of pressure in conjunction with temperature and wind speed data from two 120-m meteorological towers in an agricultural region, one outside of a large wind farm (characterizing a natural boundary layer) and one within a large wind farm (characterizing a wind farm boundary layer). Pressure fluctuations were measured over 30-minute to 1-hour periods to identify typical flow characteristics of daytime and nighttime conditions in each tall tower location. Pressure perturbations created by turbines at night contain higher contributions of energy over a broader range of frequencies than pressure fluctuations measured in the natural boundary layer not influenced by wind turbines, which supports a greater TKE redistribution by pressure perturbations. Future research will look at wind farm influences on other TKE budget terms, such as momentum flux.
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