Hydrodynamic instabilities and flow modification caused by preferential concentration of inertial particles

1233793科赫实验研究表明，即使当颗粒体积浓度相对较小时，直径为10微米至1 mm的悬浮颗粒的存在也会极大地改变气流。 这种载有颗粒的气流出现在许多工业过程中，例如循环流化床和使用气体输送固体颗粒的过程。 尽管这些流动的重要性和记录的固体颗粒的影响，仍然缺乏对颗粒影响气体流动的物理机制的理解。 本研究项目将阐明其中一种机制。 离心力倾向于将颗粒从强烈旋转的流动区域排出;然后颗粒在由应变流动主导的中间区域积聚。 研究人员假设，作用在更集中区域的重力可以加强原始气流，导致具有不均匀颗粒分布的强烈波动气流。 的物理机制将被揭示通过线性稳定性分析，从一个简单的基本状态的条件下，颗粒浓度和气体速度的小扰动的增长的研究，其中颗粒浓度是均匀的，气体正在经历剪切流的气体速度是空间位置的线性函数。 分析研究将补充下，许多相互作用的固体颗粒的影响下的气体速度的非线性动力学的数值模拟。 模拟将提供一个测试的分析理论，同时也揭示了复杂的流动时，发展的扰动增长超出线性稳定性分析的范围。根据这些研究所获得的见解，将建立一个模型，重力惯性粒子对湍流的影响。 该模型将基于快速变形理论，其中小涡流及其相关的颗粒密度波动主要受较大涡流产生的局部线性流的影响。 大尺度流动将被模拟为由应变和旋转流动的交替周期组成。 由此产生的统计理论将进行测试和完善，使用完整的数值模拟的气体颗粒混合物受到随机各向同性的力量，产生湍流。 该项目将揭示一种新的物理机制，通过这种机制，气相湍流是由作用于集中在气流非旋转区域的颗粒上的重力产生的。 这种对颗粒湍流的新的定性理解将有助于工程师设计许多工业过程，如汽车，飞机和火箭发动机;工业炉;以及用于化石和生物可再生能源转换和化工厂的流化床。 为了帮助学生理解颗粒流的复杂性，该项目中开发的模拟将被纳入一个教育模块，教授气体颗粒流的性质如何受到颗粒大小的影响。 本课程将使用SimCafe进行传播，SimCafe是康奈尔大学正在开发的基于维基的在线教学和模拟资源。

1233793KochExperimental studies reveal that gas flows can be greatly altered by the presence of suspended particles with diameters of 10 microns to 1 mm even when the concentration of particles by volume is relatively small. Such particle-laden gas flows arise in many industrial processes such as circulating fluidized beds and processes that use gas to convey solid particles. Despite the importance of these flows and the documented influence of solid particles, there remains a lack of understanding of the physical mechanisms by which particles influence gas flows. This research project will elucidate one such mechanism. Centrifugal forces tend to expel particles from regions of a flow that are strongly rotating; the particles then accumulate in intermediate regions dominated by straining flows. The researchers postulate that the gravitational forces acting on the more concentrated regions can reinforce the original gas flow leading to a strongly fluctuating gas flow with an inhomogeneous particle distribution. The physical mechanism will be revealed through a linear stability analysis, a study of the growth of small perturbations in the particle concentration and gas velocity from a simple base state condition where the particle concentration is uniform and the gas is undergoing a shearing flow where the gas velocity is a linear function of spatial position. The analytical study will be complemented by a numerical simulation of the nonlinear dynamics of the gas velocity under the influence of many interacting solid particles. The simulations will provide a test of the analytical theory while also revealing the complex flows that develop when the perturbations grow beyond the scope of the linear stability analysis. Building upon the insight obtained these studies, a model will be developed for the effect of gravitational-inertial particles on turbulent flows. This model will be based on rapid distortion theory wherein a small eddy and its associated particle density fluctuations are influenced primarily by a local linear flow produced by larger eddies. The large scale flows will be modeled as consisting of alternating periods of straining and rotational flows. The resulting statistical theory will be tested and refined using full numerical simulations of a gas-particle mixture subject to random isotropic forces that produce the turbulence. The project will reveal a new physical mechanism by which gas phase turbulence is produced by the gravitational forces acting on particles that concentrate in non-rotating regions of a gas flow. This new qualitative understanding of particle-laden turbulent flows will aid engineers designing many industrial processes such as automotive, aircraft, and rocket engines; industrial furnaces; and fluidized beds used in fossil and biorenewable energy conversion and in chemical plants. To help students understand the complexities of particle-laden flows, the simulations developed in the project will be incorporated in an educational module teaching how the nature of gas-particle flows is influenced by particle size. This lesson will be disseminated using SimCafe, a Wiki-based online resource for teaching and simulation being developed at Cornell.