Characterization of wind turbulence near New Zealand shelterbelts

Abstract

Studies were conducted to characterize the flow-field near shelterbelts to understand the atmospheric transport and diffusion of airborne agricultural particulates such as spray drift, pollen, and dust. Sonic 3-D anemometers collected velocity data at 10 Hz for five minutes each at four heights and five locations downwind and six locations upwind of a 5-m tall (=H) deciduous shelterbelt. Velocity vectors, turbulence intensities, and turbulence scales were calculated to determine air flow direction, energy transfer, and eddy size. Results showed that the approaching flow field diverged at the shelterbelt, with increased downward and upward flow compared to an open field. In the lee of the shelterbelt, the flow remained non-laminar with lower turbulence intensity to 3H. There was considerable reduction in the size of the turbulent structures behind the shelterbelt that reached a minimum at about 2H downwind of the shelterbelt. Turbulence intensity reached a maximum at about 6H, likely due to re-attachment of the stream that had deflected over the top of the shelterbelt. This information will be incorporated into models that can account for particle capture by shelterbelt canopies to better predict atmospheric transport of agricultural pollutants, and to identify the impact of agroforestry on such phenomena.