Manipulating structures & superstructures in turbulent Rayleigh-Bénard & Taylor-Couette flow with the help of stripy wall roughness.

Taylor-Couette （TC）流，即两个同轴同向或反向旋转的圆柱体之间的流动，以及Rayleigh-B - enard （RB）流，即一个盒子里从下加热、从上冷却的流动，是流体物理学中的典型系统。当受到足够强的驱动时，在这两种情况下，流动都变得紊流，在这两种情况下，结构甚至上层结构都可以演变，强烈地影响流动的输运性质。在TC流中，这些是所谓的泰勒涡，而在RB流中，这些是对流涡旋，当横向剪切时，它们在剪切方向上拉长。在SPP1881项目的第一轮中，我们对剪切RB流中的传热和流动组织进行了数值分析，并对粗糙壁面的TC流进行了数值研究，在此基础上，在第二轮项目中，我们希望利用空间周期性壁面粗糙度（条纹）来操纵流动结构和上层结构，从而控制湍流TC和剪切RB流的传递特性。本数值项目的目的是了解TC和剪切RB流中结构的自然长度尺度与条纹粗糙度施加的长度尺度之间的竞争，从而触发局部增强的羽流发射。我们的假设是，流动（超）结构能够在一定程度上遵循所施加的周期性，但是一旦内部和外部施加的长度尺度之间的不匹配太大，这将不再是可能的。在任何情况下，通过修改条纹来调整流的传输属性可以为许多应用打开大门。数值计算将与Roberto Verzicco密切合作，使用基于有限差分格式的高性能代码完成，通过浸入边界方法体现条纹粗糙度。Roberto Verzicco积极参与了这个项目。TC流的结果将与在Twente紊流Taylor-Couette （T3C）设备上进行的相应实验进行比较，在T3C设备上，我们将在圆柱体上使用条纹砂纸粗糙度。就像第一轮SPP1881一样，我们将与其他几个SPP项目密切互动。关于RB流，这些是Olga Shishkina， Eberhard Bodenschatz和Stephan Weiss，他们都在G ø ottingen，以及Bettina Frohnapfel （Karlsruhe）和Christoph Egbers （Cottbus）的TC流。

Taylor-Couette (TC) flow, the flow between two coaxial co- or counter-rotating cylinders, and Rayleigh-B ́enard (RB) flow, the flow in a box heated from below and cooled from above, are paradigmatic systems in physics of fluids. When driven strongly enough, in both cases the flow becomes turbulent and in both cases structures or even superstructures can evolve, strongly af- fecting the transport properties of the flow. In TC flow, these are the so-called Taylor vortices and in RB flow the convection rolls, which when laterally sheared elongate in shear direction.While in the first round of the SPP1881 program we have numerically analysed the heat transfer and flow organization in sheared RB flow and numerically studied TC flow with rough walls, building on this, in this second round of the program we want to utilize spatially periodic wall roughness (stripes) to manipulate the flow structures and superstructures and thus the transfer properties of the turbulent TC and sheared RB flow. The objective of this numerical project is to understand the competition between the natural length scale of the structures in TC and sheared RB flow with the imposed length scale by the stripy roughness, which triggers locally enhanced plume emission. Our hypothesis is that the flow (super)structures are able to follow the imposed periodicity to some degree, but once the mismatch between the internal and externally imposed length scales is too large, this will no longer be possible. In any case, the tuning of the transfer properties of the flow by modifying the stripiness can open the door to many applications.The numerical calculations will be done with a ultra-high-performance code based on a finite- difference scheme with the stripy roughness embodied through immersed boundary methods, in close collaboration with Roberto Verzicco, who is intensely involved in this project. The results for the TC flow will be compared with corresponding experiments with the Twente Turbulent Taylor-Couette (T3C) facility, where we will employ stripy sandpaper roughness at the cylinders.Just as in the first round of SPP1881, we will closely interact with several further SPP projects. On RB flow, these are those of Olga Shishkina, Eberhard Bodenschatz and Stephan Weiss, all in G ̈ottingen, and on TC flow those with Bettina Frohnapfel (Karlsruhe) and Christoph Egbers (Cottbus).