Collaborative Research: Dust Entrainment Processes by Convective Vortices and Localized Turbulent Structures: Experimental and Numerical Study

大气中的尘埃在调节天气、空气质量和气候方面起着重要作用。大多数关于地表尘埃放样的研究都集中在稳定的风条件下。然而，还有其他类型的扬尘机制的明显例子，例如在风流更复杂的情况下发生的沙尘暴。这项研究项目将把高分辨率数值模拟与实验室实验相结合，研究沙尘暴和对流涡旋以及它们是如何将沙尘从表面卷走的。该项目的长期影响将是改进对沙尘夹带的预测，这将对气候产生重大影响。研究小组还将与研究生和本科生一起进行重要的教育和外联工作，向K-12学生进行外联，并举办一个包括国际合作伙伴在内的虚拟小型研讨会。该项目计划通过招收代表性不足的本科生的具体项目来增强多样性。该项目的主要目标是识别和描述在非平衡条件下触发尘埃卷吸的基本机制，这些非平衡条件背离了假设空间均质性和统计平稳性的充分发展的边界层流的典型、充分调查的情景。非平衡状态的一个例子是沙尘暴，它是一种可以卷起大量尘埃的涡旋结构。研究小组将通过实验室实验和数值模拟相结合的方式，描述和确定单个扬尘过程在沙尘暴和对流涡旋携带泥沙的物理过程中的作用。实验室实验装置由涡流发生器和三维粒子图像测速系统(PIV)和粒子跟踪测速系统(3D-PTV)组成。该项目的计算方面将使用由其中一名研究人员共同开发的开源光谱元素法(SEM)代码Nek5000。本文将利用实验室和数值计算技术来回答以下问题：1.非正则涡流中，载流湍流的平均和脉动特性的水平空间不均匀对扬尘机制有何影响？气动力、压力梯度、内聚力、重力和电场力等相互竞争的力量在扬尘过程中的作用是什么？2.颗粒大小、斯托克斯数和粒度分布形态的作用是什么？对于不同大小的惯性颗粒，其主要机理是不同的还是相似的？3.在多相流湍流的表示中，实验结果和计算结果之间应该有什么样的一致性？不确定性的来源和价值是什么？4.建模的含义是什么？全球(局部)泥沙通量与全球(局部)涡流变量的相关性如何？这一信息对于开发用于模拟模型的改进的泥沙通量参数是至关重要的。该奖项反映了NSF的法定使命，并通过使用基金会的智力优势和更广泛的影响审查标准进行评估，被认为值得支持。

Dust in the atmosphere plays a significant role in modulating weather, air quality, and climate. Most studies of the lofting of dust from the surface have focused on steady wind conditions. However, there are obvious examples of other types of dust lifting mechanisms, such as dust devils, that occur in situations where the wind flow is more complicated. This research project will combine high-resolution numerical modeling with laboratory experiments to study dust devils and convective vortices and how they entrain dust from the surface. The long-term impact of the project will be to improve the prediction of dust entrainment, which has a significant climate impact. The research team will also conduct a significant education and outreach effort, with graduate and undergraduate students, outreach to K-12 students, and a virtual mini-symposium including international partners. The project plans to enhance diversity through specific programs that recruit underrepresented undergraduate students.The primary objective of this project is to identify and characterize the fundamental mechanisms triggering the entrainment of dust in the non-equilibrium conditions that depart from a canonical, well-investigated scenario of a fully-developed boundary layer flow that assumes both spatial homogeneity and statistical stationarity. An example of a non-equilibrium condition is a dust devil, which is a vortical structure that can lift significant amounts of dust. The research team will, through a combination of laboratory experiments and numerical simulations, characterize and identify the role of individual dust lifting processes in the physics of sediment entrainment by dust devils and convective vortices. The laboratory experimental setup consists of a vortex generator with three-dimensional particle image velocimetry (PIV) and particle tracking velocimetry (3D-PTV) systems. The computational aspect of the project will use an open-source spectral-element method (SEM) code Nek5000 which was co-developed by one of the researchers. The laboratory and numerical techniques would be used to answer the following questions:1. What is the effect of a horizontal spatial inhomogeneity of mean and fluctuating properties of the carrier flow turbulence on dust entrainment mechanisms in non-canonical vortex flows? What is the role of the competing forces, such as aerodynamic, pressure gradient, cohesion, gravity and electric forces in the dust entrainment processes?2. What is the role of the particle size, Stokes number and the size distribution modality? Would the main mechanisms be different or similar for inertial particles of different sizes?3. What kind of agreement is expected between experimental and computational results in a representation of multiphase flow turbulence? What is the source and value of uncertainties?4. What are the implications for modeling? How well the global (local) sediment fluxes are correlated with the global (local) vortex flow variables? This information is critical for developing improved sediment flux parameterizations for simulation models.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.