Control of Near-wall Turbulence by Stabilizing Saddle-type Steady Flow

稳定鞍型稳流控制近壁湍流

基本信息

批准号：
13650183
负责人：
KAWAHARA Genta
金额：
$ 2.11万
依托单位：
Kyoto University
依托单位国家：
日本
项目类别：
Grant-in-Aid for Scientific Research (C)
财政年份：
2001
资助国家：
日本
起止时间：
2001 至 2003
项目状态：
已结题

项目摘要

In this project we first searched for saddle-type steady flows in a plane Couette system. We obtained quiescent states of the saddle type which appeared transiently in direct numerical simulations of turbulent flow, and then the quiescent states were used as an initial guess for the Newton iteration to numerically compute three-dimensional saddle solutions to the incompressible Navier-Stokes equation. At the lowest Reynolds number for self-sustaining turbulence we have also succeeded in numerically obtaining unstable periodic motion embedded in the Couette turbulence by using the original iterative method with the aid of the direct numerical simulations. This periodic saddle is a three-dimensional periodic solution, and it represents well the regeneration cycle of near-wall coherent structures, i.e., streaks and streamwise vortices. In order to demonstrate similarities of the saddle solutions obtained in the Couette system with those in a plane Poiseuille system we next compared their … More properties with those in a fully turbulent state of these systems. It has been found in the comparison that the mean velocity and the RMS velocities in the buffer region of near-wall turbulence are in excellent agreement with the corresponding velocities of the saddle solutions.On the other hands, we introduced a porous wall into boundary-layer flow to retard a flow separation (or equivalently to enhance momentum transfer), and we observed the significant effects of the wall porosity. We also obtained analytically the unstable eigensolutions to corrugated vortex sheets, which are a model for the near-wall streaky flow, at a long-wavelength limit. In this analysis we have elucidated theoretically the destabilization mechanism of the steaks, and we have found that the saddle-type steady state appears as a nonlinearly saturated state of unstable perturbations. Furthermore, we performed the direct numerical simulations of the flow downstream of a backward-facing step, and we have shown the generation mechanism of three-dimensional vortical structures appearing downstream of the step.We have worked on the stabilization of the saddle (unstable) solutions using the Pyragas' external-force method, and in the numerical experiments of the Couette system we have succeeded in the stabilization of the periodic saddles. In this strategy we can stabilize saddle solutions by small control input. Less

在这个项目中，我们首先搜索了平面couette系统中的马鞍型稳定流。我们获得了鞍类型的静态状态，该状态在湍流的直接数值模拟中瞬时出现，然后将静态状态用作牛顿迭代的初始猜测，以数值对不可压缩的Navier-Stokes方程进行数值计算三维马鞍溶液。在自我维持的湍流的最低雷诺数下，我们也成功地通过直接数值模拟了原始迭代方法，通过使用原始迭代方法在数值上获得了不稳定的周期性运动。该周期性鞍座是三维周期性解决方案，它很好地表示近壁相干结构的再生周期，即条纹和流向涡流。为了证明在COUETTE系统中与平面Poiseuille系统中获得的马鞍溶液的相似性，我们接下来将它们的……更多的属性与这些系统完全湍流状态的属性进行了比较。在比较中发现，近壁湍流缓冲区中的平均速度和RMS速度与鞍溶液的相应速度非常吻合。在另一只手中，我们将多孔的壁引入边界壁中，以延伸流动分离（或等效地增强动量转移的速度），并且我们观察到了重要的效果。我们还分析了对波纹涡流板的不稳定征收的征收，这是近壁条流的模型，该模型是长波长极限的。在此分析中，我们阐明了牛排的不稳定机理的理论，我们发现马鞍型稳态似乎是不稳定扰动的非线性饱和状态。此外，我们对向后的步骤进行了直接的数值模拟，我们已经展示了该步骤下游的三维涡流结构的生成机制，我们在使用Pyragas的外部实验中稳定了鞍座（不稳定）溶液的稳定（Unclencization），并在稳定下进行了数字实验。马鞍。在这种策略中，我们可以通过小型控制输入来稳定马鞍解决方案。较少的