Numerical simulation study of the airflow field on a sand dune with upright fence at upper windward slope

1State Key Laboratory of Earth Surface Processes and Resource Ecology, MOE Engineering Research Center of Desertification and Blown-sand Control, Beijing Normal University, Beijing, China, 2Institute of Mechanics, Chinese Academy of Sciences, Beijing, China

Abstract: Numerical simulation is an effectual means to explore the topographic dynamics of aeolian geomorphology and blown sand control engineering. Making use of numerical simulation method and by comparing the near surface airflow field above different windward dune slope with or without upright fence at the upper windward slope, this study discussed the airflow conditions of the formation and development of "fence dune" that existed extensively at the front edge of the protective systems in desert regions, such as the protective system of Shaopotou section of Baotou-Lanzhou railway at southeast fringe of the Tengger Desert and the protective system along the highway across the Taklamakan Desert. The results showed that effect of upright fence at the upper windward slope on airflow field was mainly embodied as the separation of airflow in advance or else it would happen at the downwind crest of the dune, as well as the formation of small vortexes at the lee side of the fence, which led to the superimposition of backflow zone at the lee side of the fence to that at the lee of the dune and made it higher and longer. Blocking of blown sand on windward slope by fences and enlargement of backflow zone on lee slope would alter evolution of the dune morphology gradually. This kind of dunes developed due to the presence of upright fences was generally characterized by taller and near symmetric transection compared with those natural transverse dunes without fences. Once formed, with the increase of windward slope, backflow zone at the lee of the dune became higher and longer until the windward slope was larger than 15 that backflow field at the lee would change little. It is clear that fence dunes at the front of protective system altered local airflow field. To make clear whether and how the fence dunes impact near surface airflow in the downwind protective system, further observation or numerical simulation study is needed.
Key words: Upright fence; fence dune; near surface airflow field; numerical simulation