A CFD study of wind patterns over a desert dune and the effect on seed dispersion |
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Authors: | Eugéne C Joubert Thomas M Harms Annethea Muller Martin Hipondoka Joh R Henschel |
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Institution: | 1. Department of Mechanical and Mechatronic Engineering, Stellenbosch University, C/o Banhoek and Joubert Street, Stellenbosch, 7600, South Africa 2. Environmental and Geographic Department, University of Namibia, Windhoek, Namibia 3. Gobabeb Training and Research Centre, Desert Research Foundation of Namibia, Windhoek, Namibia
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Abstract: | In the Namib Desert seed distribution is greatly influenced by wind patterns. Existing literature regarding wind patterns
over dunes focuses on two-dimensional simulations of flow over simplified dune structures. The three-dimensional geometries
of the sand dunes suggests far more complex flow features exist, which are not captured by two-dimensional simulations. Computational
fluid dynamics (CFD) was used to reproduce the three-dimensional near surface wind patterns around a dune with the aim to
learn more about seed distribution. Field work included terrain mapping, wind speed, direction and temperature metering. The
CFD results show the expected two-dimensional flow features of high pressure at the dune toe, low pressure at the crest and
flow acceleration up windward slope. Also observed are some three-dimensional flow features such as a spiral vortex near the
crest and transverse flow due to crest-line curvature of the dune. It was also observed how the wall shear stress differs
due to the three-dimensional shape of the dune. The wall shear stress suggests that seed accumulation is more likely to occur
behind trailing (down-wind) crest edges. Particle tracking showed how seeds tend to move over the dune crest and recirculate
towards the crest on the lee-side. The study showed that adding the third dimension makes the simulations more complex, adds
to computational requirements and increases simulation time but also provides vital flow information which is not possible
with two-dimensional simulations. |
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