边界层转捩过程三维扰动的发展和演化

引入展向调制的二维人工扰动激发平板边界层转捩,利用水槽氢气泡流动显示技术观察到转捩边界层中典型三维扰动的产生和发展,包括Λ结构、发卡涡以及发卡涡演化生成环状涡的过程.实验结果显示出环状涡和尖峰结构的关系,直接证实了尖峰结构的产生机理.在流动紊乱化初始阶段发现常出现在湍流边界层中的暗斑结构,结果表明与暗斑相伴随的局部高剪切层不稳定可能是流动紊乱化的重要原因.

Developments and Evolutions of Three-Dimensional Perturbations in Transitional Boundary Layer

Formations and developments of typical 3-D perturbations, typically shown as Λ structures, hairpin vortices and ring-like vortices, were observed by means of hydrogen-bubble method in a transitional flat-plate boundary-layer excited by a modulated 2-D artificial perturbation. Visual results show the relationships between a hairpin vortex and a spike structure, which convince the forming mechanisms of spike structures. Dark spots, often detected in turbulent boundary layer, are also observed during flow breakdown, and results show that the instability of local high-shear layer caused by dark spots is probably responsible for flow breakdown.