金字塔沙丘地表气流场及其动力学过程研究

THE FLOW FIELD AND ITS DYNAMICS PROCESSES OF PYRAMIDAL DUNE

沙丘沉积构造指示及风洞实验结果表明：莫高窟顶金字塔沙丘形成于３组风向条件下（ＮＥ、ＳＷ及ＮＷ），是链状沙丘的一种变形、分离形式。从沙丘形态特征分析，三面体金字塔沙丘及其它复杂沙丘类型（线形、格状、多面体金字塔沙丘）之间存在某种内在本质的联系。即多信风条件下产生的风向组合，通过主、副脊（梁）的不同形式发育组合过程，形成适应于地表气流的地貌形态。同时认为：沙丘沉积构造及风洞实验相结合的综合研究比以往单一过程研究更为全面、系统、深刻。

The paper, based on wind tunnel experiment and sedimentary structure determination to the pyramidal dunes on top of Mogao grotto of Dunhuang, aims at re establishing the flow field of pyramidal dune surface and further discussing the dynamics processes of dune forming and evolution. \ \ The pyramidal dunes on top of Mogao grotto are formed in condition of wind blowing from three directions including NW, NE and SW. NE and SW wind directions have blow out the dune's main arm in E-NW direction, and WN wind direction has formed the secondary arm of it. The dynamics processes of pyramidal dune are that main arm deforms then produce secondary arms. The acting of special assembling circulation' and diffusing circulation' of pyramidal dune is the key force for dune's top forming. In the forming of pyramidal dune, the effective angle between flow direction and dune ridge must be more than 30°. Under this condition, an inverse accelerating flow velocity belt appears at leeward side of dune, which makes sand materials develop upward from the two sides of dune ridge. Otherwise, the dune will develop longitudinally. In the views of eolian landforms and evoluting processes, it is thought that some internal relations are existed among complicate sand dunes. One combination of multi direction wind regime can form a landform suitable to surface circulation in the processes of main and secondary arms (ridges) evoluting. When wind regime changes, the type of sand dune will evolute to another type suitable to the relative surface circulation. In return, landform is also the important factor determining the environmental wind regime. The integrated research combining sedimentary structure determining and wind tunnel experiment is suggested to be a more all round, systematic and further method than before single process research.