风沙流/沙尘暴流场特性及其湍流结构的测量与分析

As a typical environmental disaster that has a wide-ranging influence, windblown sand flux/dust storms can be categorized into solid-gas two-phase flow taking place in the atmopsheric boundary layer with a high Reynolds number up to 10^8. Understanding and recognizing the turbulent structures and flow features within this phenomenon are of great benefit to its prediction and prevention. This project is proposed to develop a 'Pyramid-type Observation Arrays' to fulfill real-time and synchronous measurements of the key physical quantities of windblown sand flux/dust stomrs, including wind velocity, dust concentration, temperature and humidity, and to accumulate valid data of zero-pressure-gradient and near-neutral wall turbulence with high Reynolds number during windblown sand flux/dust storm events through wind tunnel experiments and field observations with effective exclusion of uncontrollable factors. Based on this, mean velocity profile and scaling law of windblown sand flux/dust storms can be analyzed so as to reveal the characteristics of wind fluctuations and wind spectrum and refine the their representive models. Particular emphasis goes to the domain region of various turbulent flow structures, their interactions and corresponding variation features, as well as the transportation structure of sand/dust. Details of the interaction between the turbulent flow structure and the emission and transportation of windblown sand flux/dust storms, and the influnce of temperature and humidity to wind-sand two-phase flow will be investigated. Eventually, this project will establish a wind-velocity representive model to describe the flow field of windblown sand flux/sand storms, so as to realize accurate predicitons of natural windblown sand flux and provide an improvement to existing sand-dust forcasting schemes.

风沙流/沙尘暴是发生在大气边界层的一种雷诺数高达10^8的气固两相流，也是影响范围较广的一种环境灾害，深刻认识其流场特性和湍流结构有助于对这类灾害的预报和防治。本项目通过研发一种"金字塔形观测阵列"以实现对风沙流/沙尘暴流场的风速、沙尘浓度、温湿度的实时同步观测；通过对可控条件下的风洞实验和野外不可控因素影响的排查，获得并积累零压力梯度近中性条件下高雷诺数壁湍流在风沙流/沙尘暴情形的有效数据。由此分析风沙流/沙尘暴流场的平均流形式和标度特性；提炼其风速脉动和风速谱的变化特征和表征模型；揭示其不同湍流结构存在的区域、相互作用规律及其变化特征以及沙尘输运的流动结构；探讨风沙流/沙尘暴流场湍流结构与沙尘起动和输运的相互影响，以及影响地表风沙两相流运动温度和湿度的变化规律。在此基础上，建立风沙流/沙尘暴流场的一个风速表征模型，实现对自然风沙流输沙率的预测，并为沙尘暴预报模式的改进提供一种依据。

风沙流/沙尘暴是发生在大气边界层的一种高雷诺数气固两相流，也是影响范围较广的一种环境灾害，深刻认识其流场特性和湍流结构有助于对这类灾害的预报和防治。本项目在甘肃民勤青土湖干涸平坦的湖床上建立了可用于高雷诺数大气表面层净风及风沙流/沙尘暴观测的野外观测列阵——“青土湖观测列阵”（QLOA），实现了对风沙流/沙尘暴流场的风速、沙尘浓度、温湿度的实时同步观测，获得了超过7400小时的多物理量同步数据，数据总量超过4.7TB，共观测到沙尘天气事件58次。通过对可控条件下的风洞实验和野外不可控因素影响的排查，获得并积累了零压力梯度近中性条件下高雷诺数壁湍流在风沙流/沙尘暴情形的高质量数据172小时，净风数据422小时。基于这些高质量数据，利用统计分析、谱分析等手段研究了风沙流/沙尘暴流场的湍流特性，发现：含沙流动中卡门常数增大约为0.44，同时湍动能显著增加；大气表面层中超大尺度结构存在自上向下的演化机制；沙尘暴中超大尺度结构的三维尺度与净风流动情形差异不明显，但结构倾角明显增大；超大尺度结构主导了沙尘暴中沙尘的流向输运；沙尘暴中流向电场强度高于垂向电场。利用风洞风沙流实验，分析了沙粒运动过程中的关键参数，包括冲击、起跳速度和角度等。结合实验结果和理论分析，建立了近地表风速的表征模型；提出了基于电场强度观测的沙尘暴预警策略，通过模拟验证证实风速预测模型及沙尘暴预警策略有很好的预测精度。这些结果有助于沙尘暴预报模式的改进及沙尘暴的准确预报。

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