PM2.5在弯道所致湍流中的多尺度动力学机制

Current research on mist, fog & PM2.5 concentrates on its outdoor performance. However, it can easily disperse into indoor environment where people spend 80% of their life time. As a result, it is quite important to investigate its evolution and transportation phenomena from outdoor to indoor or from one spaces to another enclosed spaces. The investigation on its dynamics through indoor ventilation systems, however, has just started up, especially for particle nucleation, growth, evolution and transportation in ventilated bends.. Therefore, present project aims to study the nano- and micro- particle dynamics with multi-scales in bend-induced turbulent flow based on our previous study foundations. In detail, the bend-induced turbulence will be solved by a Large Eddy Simulation (LES) method with a dynamic subgrid model, which will reveal the specific flow vortex structures and developing turbulence characteristics. With tracking the Lagrangian path of turbulent micro-cell fluid, particle nucleation, growth and evolution will be modeled and simulated by stochastic method in each cell. Comparing the turbulence and particle simulation results with experimental data, we will analyze the effects of bend geometric parameters, flow characteristics and corresponding particle features on particle evolution and transportation. Finally, we plan to propose several simple, efficient and general parameterization solutions or semi-analytical formula to describe and predict the particle dynamics throughout bends. These semi-analytical solutions will benefit massive engineering applications. . For understanding and controlling current severe mist and frog in our indoor fresh air, the above basic study can provide theoretical support and application foundation, especially in particle-laiden ventilation regulation, nano-surface & particle interaction and PM2.5 filtration.

目前对雾霾PM2.5的研究关注主要在室外，但其极易扩散到人们80%以上生活时间的室内，因而对其向室内演化扩散等动力学机制研究特别重要。然而对室外向室内或室内之间通过通风系统交叉污染的研究近年才起步；特别是对颗粒影响显著的弯道随处可见，但尚无专门针对颗粒在不同通风弯道湍流中生成演化扩散的系统研究。因此本项目将在已有前期研究基础上，开展弯道湍流与多尺度颗粒动力学作用机理研究。对弯道所致湍流采用动态亚尺度大涡模拟求解典型弯道流场中涡结构变化和非各项同性边界层的发展；然后采取Lagrangian方法追踪流体-颗粒微团轨道，随机模拟PM2.5的生长演化和温湿度影响等动力学过程；最后通过实验、模拟和解析系统综合分析弯道不同几何参数、湍流场特征、颗粒特征和流场-颗粒结合特性，并获得大规模应用简单通用的参数方案和分析模型。以上研究可给通风调节、壁面处理和颗粒过滤等控制PM2.5污染提供应用基础和理论支撑。

雾霾PM2.5等悬浮颗粒的已有研究大部分关注室外大空间和时间范围的情况，然而人们80%以上的时间在室内度过，特别是在由机动车/燃烧/扬尘等带来雾霾较大的冬季，因此研究室内外源头的颗粒到室内或关键表面的扩散演化等动力学机理和相应的影响控制模型就显得特别重要。室内外之间、室内各部分空间之间交叉通风贡献和颗粒传播源贡献率的研究因雾霾的原因近年在国内成为研究热点。但是尚无系统地对室外到建筑表面再到通风弯管的湍流和多尺度颗粒动力学相互作用的机理和应用研究。因此本项目在原有研究基础和基金项目规划上，开展了不同弯道和绕流体等非完全发展湍流场、涡结构和多尺寸颗粒流动演化过程的机制研究，并开发相应的简洁有效模型供实际工程应用。对建筑外到跨弯道的湍流过程，采用大涡模拟、湍流和近壁模型等方法研究了其中的各类尺度涡结构和二次流情况。对颗粒动力学过程，采用Lagrangian等方法追踪颗粒变化沉积聚堆机制。分析微纳米颗粒随其演化、温湿度、几何结构、流场和颗粒特性的变化规律，发展了颗粒沉积聚堆和其对表面影响作用的线性和指数模型，并应用于颗粒通风和能源效率的估计。本研究所总结的半分析模型初步提出了“代表流场悬浮颗粒沉积聚堆消光效应”的上下游分析方案和实用模型，对雾霾控制、流场测试、太阳能利用、视野照明或能量辐射等领域具有一定的指导作用，可提供给大规模工程应用作参考。