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Wind and Structures   Volume 22, Number 4, April 2016, pages 477-501
Wind direction field under the influence of topography: part II: CFD investigations
S.W. Li, Z.Z. Hu, K.T. Tse and A.U. Weerasuriya

Abstract     [Buy Article]
    Though hilly topography influences both wind speeds and directions aloft, only the influence on wind speeds, i.e. the speed-up effect, has been thoroughly investigated. Due to the importance of a model showing the spatial variations of wind directions above hilly terrains, it is worthwhile to systematically assess the applicability and limitations of the model describing the influence of hilly topographies on wind directions. Based on wind-tunnel test results, a model, which describes the horizontal and vertical variations of the wind directions separately, has been proposed in a companion paper. CFD (Computational Fluid Dynamics) techniques were employed in the present paper to evaluate the applicability of the proposed model. From the investigation, it has been found that the model is acceptable for describing the vertical variation of wind directions by a shallow hill whose primary-to-secondary axis ratio (aspect ratio) is larger than 1. When the overall hill slope exceeds 20, the proposed model should be used with caution. When the aspect ratio is less than 1, the proposed model is less accurate in predicting the spatial variation of wind directions in the wake zone in a separated flow. In addition, it has been found that local slope of a hill has significant impact on the applicability of the proposed model. Specifically, the proposed model is only applicable when local slope of a hill varies gradually from 0 (at the hill foot) to the maximum value (at the mid-slope point) and then to 0 (at the hill top).
Key Words
    computation; topography; wind characteristics; direction changes
S.W. Li: 1Division of Ocean Science and Technology, Graduate School at Shenzhen, Tsinghua University, Shenzhen, P.R. China
Z.Z. Hu: Division of Ocean Science and Technology, Graduate School at Shenzhen, Tsinghua University, Shenzhen, P.R. China;
Department of Civil Engineering, Tsinghua University, Beijing, P.R. China
K.T. Tse and A.U. Weerasuriya: Department of Civil and Environmental Engineering, Hong Kong University of Science and Technology, Clear Water Bay, Kowloon, Hong Kong


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