【作者】 陈健；

【导师】 张兆顺； 崔桂香；

【作者基本信息】 清华大学 ， 流体力学， 2002， 博士

【摘要】 本文使用直接数值模拟（DNS）方法，通过谱方法结合嵌边法求解非线性的Navier-Stokes方程，来研究由圆管壁面引入的周期性吹吸（PSB）扰动作用下，圆管流动沿流向的空间演化规律及其相应的时间演化过程。本文计算中流动的雷诺数选定为3000，PSB扰动的周向波数选定为1，扰动频率选定为0.5，扰动宽度选定为。在这一组参数下，本文研究了不同扰动幅值的PSB扰动作用下圆管流动的转捩过程，首次给出圆管流动从层流转捩到湍流的时空演化全过程，发现了圆管流动的二次转捩现象，并进一步揭示了发卡涡是圆管流动转捩中的主要结构，流动的转捩过程与发卡涡的演化直接相关。此外，发卡涡与圆管流动中的高剪切层结构以及尖峰密切关联。在一定幅值的PSB弱扰动作用下，圆管流动中出现一系列发卡涡，发卡涡前缘处环形涡的形成、扩散和破裂以及发卡涡头部的破碎导致了流动的第一次失稳，产生塞流结构。塞流结构由于得不到来自上游的持续扰动激励，而其自身不具有维持其空间位置的能力，从而向下游迁移。当加大PSB弱扰动的幅值后，流动中首先出现塞流结构，即第一次转捩。随着塞流结构流出计算域，后继扰动向下游继续发展，表现为发卡涡的涡脚向壁面不断贴近，进而诱发近壁涡结构，近壁涡结构的进一步演化促使圆管流动出现二次转捩，发展到了湍流阶段。当由壁面引入PSB强扰动后，圆管流动中形成较强的发卡涡，发卡涡头部和脚部的同时紊乱化导致了流动的直接失稳。首先发卡涡的头部在向圆管中心抬升的过程中，会形成马蹄涡，马蹄涡从发卡涡头部脱离后，形成孤立的环形涡。环形涡的形成会引发发卡涡头部的破碎，破碎的小涡结构向壁面运动。发卡涡的涡脚在向下游发展的同时沿周向扩展，并诱发近壁涡，该近壁涡沿流向快速扩展。最终圆管中从壁面到中心充满各种涡结构，导致流动最终失稳。由于PSB强扰动不断激发新的发卡涡，而发卡涡的不断失稳导致了强扰动旁路转捩的失稳点靠近上游且空间位置基本固定。更多还原

【Abstract】 The present work is carried out by direct numerical simulation (DNS), the non-linear Navier-Stokes equation is formulated in terms of spectral method with fringe method. The objective of present work is to explore the spatial and temporal evolution of pipe flow with the disturbance imposed on the pipe wall in the form of periodic suction and blowing (PSB). The Reynolds number of the flow is 3000. The circumferential wave number of PSB disturbance is 1. The frequency of disturbance is 0.5. The width of disturbance is . Based on these parameters, the present work studies the transition of pipe flow with the different amplitude of PSB disturbance. The present work simulates the whole time-space process of the transition from laminar to turbulence and secondary transition phenomenon in pipe flow for the first time. The main structure in pipe flow transition is hair-pin vortex; the evolution of hair-pin vortex is related with the transition of pipe flow. Furthermore, hair-pin vortex is closely related with high-shear layer structure and spike structure in the pipe flow.When the PSB amplitude is weak, a series of hair-pin vortex will be formed. The formation, diffusion, breakup of the front edge of hair-pin vortex and the break of the head of hair-pin vortex lead to the first instability and form the slug structure. The slug structure does not get the persistent disturbance that comes from upstream and cannot hold its position by itself, so it travels to downstream. When increase the amplitude of the weak PSB disturbance, slug structure is formed in pipe flow firstly, this is the first transition. While slug structure is leaving from computing domain, the successive disturbance develop in downstream direction, the legs of hair-pin vortex approach the wall continuously and induce vortex structures near the wall. The evolution of this near-wall vortex structures brings the secondary transition to turbulence in the pipe flow. The by-pass transition appears in the pipe flow under the influence of strong PSB disturbance. The main structure in by-pass transition caused by strong PSB is hair-pin vortex. The head of hair-pin vortex rise to the center of the pipe and horse-shoe vortex is formed. Then the horse-shoe vortex detaches from hair-pin vortex and form isolated ring-like vortex. The detachment of ring-like vortex from hair-pin vortex induces the breakdown of the head of hair-pin vortex. Then the broken small vortex structures move towards the wall. When the legs of hair-pin vortex move to downstream and extend in azimuth direction, they cause the formation of the vortex structure near the wall. This near-wall vortex structure develops to downstream quickly. Finally there are many kinds of vortexes in pipe flow from the center to the wall, and the flow loses its stability. The new hair-pin vortex is formed continuous with PSB disturbance, the breakup of hair-pin vortex makes the instability position of the strong by-pass transition is immobile and near the upstream of flow.更多还原