Agglomeration and cluster formation of microscacle particles and droplets in highly loaded turbulent gas flows

该项目的目标是对湍流、高负荷分散多相流中颗粒团聚的动态过程进行建模、模拟和分析。在第一个项目阶段，基于描述复杂湍流的大涡模拟技术的四向耦合欧拉-拉格朗日方法和弥散相的同步粒子跟踪方案取得了显着进展。在对颗粒碰撞进行确定性处理的基础上，建立了两个新的团聚模型和壁面粘着模型。这些方法首先在各种测试案例和较大的参数范围内得到验证，然后成功地应用于分析高负荷流体湍流内的团聚过程。从而对颗粒团聚及其最重要的影响因素以及团聚体对湍流流场的反馈的物理关系有了新的认识。第二个项目期的目标是考虑团聚体破碎的影响，为了简化起见，它还没有考虑到，但对描述整个过程具有重要作用。在技术应用中，团聚体的生长是团聚和破碎相互作用的结果，导致了特征性的粒度分布。这反过来又决定性地决定了重要的过程，例如过滤器或旋风分离器中的分离、药物的剂量或化学反应器中的反应速率。因此，对这两种现象的描述对于高负荷湍流两相流的真实模拟是必不可少的。从三种最重要的破碎机制的列表中，我们将特别关注由于流体诱导力而导致的团聚体的破碎。偏离文献中的最新研究成果(无质量的纯小团聚体的破裂，DNSs和大部分均匀的各向同性湍流)，我们将对有质量(惯性)的团聚体的流体诱导破裂进行建模和稍后的分析，其中明确区分了可能由于粘性力而破裂的小团聚体(d&lt；柯尔莫戈洛夫长度L_k)和大团聚体(d&gt；L_k)，对于大团聚体(d&gt；L_k)，惯性力是导致可能的破裂的原因。由于它们的实际相关性，壁面剪切流是人们感兴趣的焦点。除了开发现代可持续模拟概念外，主要目标是提高对团聚体建立及其潜在破坏的物理理解。除了流体诱导的团聚体破裂外，颗粒壁面和颗粒-颗粒碰撞引起的破碎将被包括在建模概念、模拟和最终分析中。最后，实际相关的应用程序的总体概念将可用。

The objective of the project is to model, simulate and analyze the dynamic process of particle agglomeration in turbulent, highly loadeddisperse multiphase flows. In the first project period significant progress was made based on a four-way coupled Euler-Lagrange approach relying on the large-eddy simulation technique for the description of complex turbulent flows and a simultaneous particle tracking scheme for the disperse phase. On the basis of a deterministic treatment of the particle-particle collisions two new agglomeration models and a wall adhesion model were developed. These were first validated based on various test cases and for a wide parameter range and then successfully applied for the analysis of the agglomeration processes within turbulent flows of highly loaded fluids. Thereby new insights into the physical relationships concerning the agglomeration of particles and their most important influencing factors as well as the feedback of the agglomerates on the turbulent flow field was gained.The objective of the second project period is to incorporate the effect of breakage of agglomerates which for simplification purposeswas not taken into account yet, but plays a significant role for the description of the entire process. In technical applications thegrowth of agglomerates is the result of the interplay between agglomeration and breakage of the agglomerates leading to thecharacteristic particle size distribution. That in turn decisively determines significant processes such as the separation for example infilters or cyclones, the dosing of pharmaceuticals or the reaction rates in chemical reactors. Therefore, the description of bothphenomena is indispensable for a realistic simulation of highly loaded turbulent two-phase flows.From the list of the three most important mechanisms of breakage particular attention will be paid to the break-up of agglomerates dueto fluid-induced forces. Deviating from the state-of-the-art in the literature (break-up of massless and solely small agglomerates, DNSand mostly homogeneous isotropic turbulence) the fluid-induced break-up of agglomerates with mass (inertia) will be modeled and lateranalyzed, where a clear distinction is made between small agglomerates (d < Kolmogorov length l_k) which may break up due to viscous forces and large agglomerates (d > l_k) for which the inertia forces are responsible for a possible breakage. Due to their practical relevance wall-bounded shear flows are in the focus of interest. Besides the development of a modern sustainable simulation concept, the main goal is to improve the physical understanding of the build-up of agglomerates and their potential breakage. In addition to the fluid-induced breakage of agglomerates the break-up due to particle-wall and particle-particle collisions will be included in the modeling concept, the simulation and the final analysis. At the end an overall concept for practically relevant applications will beavailable.