风-沙-电多场耦合中电效应特性表征及其对沙尘输运影响的研究

Dust/sand electrification, which is a ubiquitous phenomenon in dust events such as blowing sand, dust devils, and dust storms, has a potentially dramatic effect on dust/sand lifting and transport processes. Due to the non-equilibrium, multiscale, and multi-field coupling characteristics of dust/sand electrification and the limitations of the existing measurement technologies, quantitative analysis of electrical effects in dust events and their influence on the transport of dust/sand particles are still largely unclear. This project has three-fold purpose: 1) to develop a long-term, real-time, and accurate measurement system for charge-to-mass ratio of dust/sand particles on the basis of wind-tunnel experiments, thus providing a powerful tool for measuring charge-to-mass ratio of particles in dust events and even granular materials flows; 2) to quantify charge-to-mass ratio of dust particles through a set of field observations at Qingtu Lake Observatory; 3) to explore the influences of electrical effects on dust particles transport using the multi-field coupling model (that is wind flow, particle motion, and electrostatic forces interacting with each other). This research will be helpful for assessing the underlying physical mechanism of granular materials charging and provide some theoretical insights into the prediction and prevention of strong dust events.

沙尘起电现象广泛存在于风沙流、尘卷和沙尘暴中，其对沙尘颗粒的起动和输运有重要的影响。由于沙尘起电现象本身的非平衡、多尺度、多场耦合特征以及实验测量技术的不完善，风沙电效应的定量化分析及其影响沙尘颗粒输运的具体规律还不完全清楚。本项目拟在兰州大学多功能环境风洞模拟的风沙实验环境下，发展一套长时程、实时、准确测量沙尘颗粒荷质比的系统，从而为风沙运动乃至颗粒流中颗粒荷质比的测量提供有力工具。以此为基础，进一步在兰州大学青土湖观测站开展风沙电效应的多物理量、实时、同步、全场实验观测，得到沙尘颗粒荷质比的定量表征规律。最终，运用风-沙-电多场耦合数值模型探索风沙电效应影响沙尘颗粒输运的具体规律。该研究成果将有助于揭示颗粒物质带电的物理机制，以及强沙尘天气的预测和防治。

实验观测表明沙尘暴中存在强度超过100kV/m的强电场，其对沙尘颗粒的起动和输运有显著影响。然而，目前为止，人们对于沙尘暴中沙尘颗粒的带电特性和电场分布特征还不清楚。已有研究主要关注垂向电场对颗粒输运的影响，真实的三维电场情况下颗粒的输运规律尚待阐明。本项目采用实验与数值模拟相结合的手段，分析了沙尘暴中三维电场对跃移颗粒输运的影响。通过在兰州大学青土湖观测阵列的野外观测，获得了50余场沙尘暴条件下多点、多物理量、实时、同步观测数据。基于观测数据和库伦定理，采用变分正则化原理，建立了沙尘暴电场结构和颗粒荷质比的反演模型，揭示了沙尘暴空间电荷“正负镶嵌”和空间电场“正负交替变化”的特征。采用小波变换和经验模态分解，给出了沙尘颗粒荷质比和三维电场的定量表征，并结合数值模拟揭示了风沙电效应对沙尘颗粒输运的影响。这些结果有助于人们对沙尘暴期间的沙尘运输进行更为准确的描述。