基于风沙两相流的机械固沙措施防护机理及优化研究

Mechanical sand-fixation is often used in the quicksand hazards hit areas, which is most effective key measures for the sand hazard of the desertification area. However, the existing mechanical sand-fixation measures such as clay sand barrier, straw checkerboard barriers, plastic sand barrier were all groped from practice, lack of theoretical basis and adequate comprehend of their effective and economy, which directly result that some sand-fixation method failed to achieve the goal of prevention and control of desertification, and become to desertification hazard. Although some sand-fixation methods can work normally, the high cost and shrot work life limited them to be widely used. In this project, we intend to clarify the operation mechanisms, optimize and integrate the existing mechanical sand-fixation measures of the key desertification area in Minqin by combining the results of field observations, wind tunnel experiments and numerical simulation. Through experimental observations and theoretical modeling, clarifying the law of the surface sand movement of different types of wind and sand hazard hit area, analysis the the operation mechanisms of three different typical mechanical sand-fixation measures in different sand hazard area, clarify the relationship between the mechanical behavior characteristics and micro-structure and macro-layout, the effects and mechanism role of set methods, materials, specification of the three different typical mechanical sand-fixation measures. Establishing the framework of optimal design theory in anti-desertification project, giving quantitative simulation of sand prevention and fixating structure for a typical desertification areas, providing effectiveness and economic assessment, on the basis of these results.

机械固沙通常被用于流沙危害严重地区，是风沙危害区沙漠化治理最有效的措施。现有的机械固沙措施如粘土沙障、草方格沙障、塑料沙障均为实践中摸索出来的风沙防治措施，缺乏相应的理论基础，因而对这些治沙措施的有效性经济性缺乏足够的认识，导致有些防沙治沙措施未能起到防沙治沙的作用，反而成为沙化的隐患；有些防沙治沙工程虽然取得了一定的效果，但成本太高，效果也不能持久。本项目拟采用野外观测、风洞实验和理论模拟相结合的方法，以野外观测和风洞实验结果为依托，建立模拟不同环境条件中麦草沙障、粘土沙障、塑料沙障影响下的风-沙两相流的理论模型，针对典型沙化区域防沙治沙结构给予定量模拟与评估，阐明机械固沙措施的适用条件及其铺设方法、尺寸规格等对防风固沙效应的影响，并建立典型沙化区域防沙治沙工程的优化设计理论框架。

研究机械沙障防沙治沙的机理并进行优化设计，对控制干旱区风沙灾害具有重要的意义。依托野外观测和风洞实验，对不同沙障、地表类型下地表湍流风场、沙尘通量和沙尘浓度等宏观统计量进行测量。采用实验与模拟相结合的方法，对不同形状颗粒拖曳力系数、坡面击溅函数等微观机理进行研究。在此基础上，结合大涡模拟方法和颗粒轨道模型理论，建立可描述不同地形与机械沙障影响下的风沙运动理论模型与计算程序，并由实验结果验证计算精度。面向防沙治沙工程实践，通过数值模拟研究不同地表情况下多种典型机械沙障的作用机理，在此基础上提出了相应的优化设计方案。结果表明：1）局地地形对近壁面流场中的湍流特征和沙粒的跃移运动规律影响很大，麦草、粘土、塑料三种典型机械固沙措施的保存时间及固沙效果也会受到布置地点的影响；平地测得的击溅函数并不适用于坡面的情况，本项目提出的坡面击溅函数与实验吻合良好；2）沙障网格间距、沙障网格高度和沙障渗透率是影响风流场的关键参数，合理设置参数使沙障达到最优的防沙治沙效果；新型的三角塑料沙障构型在保证防风固沙效果的同时能够节省大量材料和用工量；草方格内部存在强烈的具有很大瞬态速度的湍流流动，可以引发颗粒在草方格内部进行二次搬运，并由此形成中间低四周高的堆积形态；3）在沙漠城市人工设施的优化设计中，砖阵沙障阵列应放置于上风向位置防沙和固沙，建筑物阵列应放置于下风向位置而板阵列应放置在沙粒易堆积位置。以上的结论的获取将为机械沙障的实际工程应用提供新的科学理论和技术支持。