High-Schmidt number turbulent mixing as an aggregation process

湍流中被动平流物质的混合是一个基本过程，在许多地球物理、工业、自然或人造应用中无所不在。当混合标量浓度的扩散系数小于平流流体的运动粘度时，底层搅拌场和最终扩散过程的运动之间的相互作用是不平凡的，即在施密特数远大于1时的所谓巴彻勒制度。在这种情况下，浓度场自组织，低于速度场的最小漩涡的大小，作为一组片，聚集，因为他们消失，从而建立了混合物的浓度含量。在本项目中，我们希望结合联合收割机实验室实验和直接的数值模拟，以探索更详细的混合作为一个聚集过程的这一愿景，并将其扩展到三维的情况下。将在尽可能简单的流动配置中，通过实验和模拟系统地研究不同标量源以及不同施密特数和雷诺数的影响，以解决整个过程的基本问题。我们的目标将是在聚集模型的基础上，在高施密特数的粘性对流范围内的标量统计的完整描述。

The mixing of passively advected substances in turbulent flows is a fundamental process omnipresent in many geophysical, industrial, natural or man-made applications. The interplay between the motions of the underlying stirring field and the ultimate diffusive process is non-trivial when the diffusivity of the mixed scalar concentration is smaller than the kinematic viscosity of the advecting fluid, the so-called Batchelor regime at Schmidt numbers much larger than unity. In this regime, the concentration field self-organises, below the size of the smallest eddies of the velocity field, as a set of sheets, aggregating as they fade away, thus building up the concentration content of the mixture. In the present project, we want to combine laboratory experiments and direct numerical simulations in order to explore in more details this vision of mixing as an aggregation process, and extend it to the three-dimensional case. The impact of different scalar sources as well as of different Schmidt and Reynolds numbers will be studied systematically, both in experiment and simulation, in flow configurations kept as simple as possible, in order to address the fundamentals of the overall process. The goal will be a complete description of the scalar statistics in the viscous-convective range at high Schmidt numbers on the basis of the aggregation model.