Resonant growth of three-dimensional modes in trnsitioning Blasius boundary layers
Resonant growth of three-dimensional modes in trnsitioning Blasius boundary layers
复制标题
Blasius 边界层转变中三维模式的共振生长
DOI：
10.1017/s0022112089003058
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发表时间：
1989
影响因子：
3.7
通讯作者：
R. Mangano
中科院分区：
文献类型：
--
作者：
T. Corke;R. Mangano
通过仔细控制二维和三维同步扰动的相耦合输入，研究了边界层层流的非线性演化和击穿。这涉及到平面托尔曼-施里希廷波和斜波对的产生，以促进近共振条件，这种条件在理论上已被证明会导致不稳定边界层中三维的快速发展。特别强调了两个突出的机制，即Orr-Sommerfeld模态的共振三联性和顺流周期性流动对展向周期性三维扰动的二次不稳定性。这些机制对输入扰动的振幅和波数的敏感性是特别关注的。在层流边界层中临界层的近似高度处，利用悬挂在壁面上方的一组沿展向排列的线加热器来同时产生二维和三维波。这些操作是为了通过局部加热产生时间周期展向相变速度扰动。本文重点讨论了波数为（α, 0）的基本平面波和次谐波斜波对（½α，±β）的联合作用力所得到的条件。结果记录了能量在次谐波模式下的共振增长，与种子±β条件相匹配的横流尺度交错λ涡旋模式的形成，以及它们随后向湍流的转变。在这些不同阶段的流场的完整文件是通过烟丝流可视化和通过在三个空间维度上测量所有三个速度分量的相位条件热线测量来呈现的。
By carefully controlled phase-coupled input of simultaneous two- and three-dimensional disturbances, the nonlinear evolution and breakdown of the laminar flow in a boundary layer was examined. This involved the generation of plane Tollmien–Schlichting waves and pairs of oblique waves so as to promote nearresonance conditions which have been theoretically shown to lead to the rapid development of three-dimensionality in unstble boundary layers. Special emphasis is placed on the two prominent mechanisms, namely resonant-triads of Orr–Sommerfeld modes and the secondary instability of the streamwise periodic flow to spanwise periodic three-dimensional disturbances. The sensitivity of these mechanisms on the amplitudes and wavenumbers of the input disturbances was of special focus. The simultaneous two- and three-dimensional wave generation was accomplished using a spanwise array of line heaters suspended just above the wall at the approximate height of the critical layer in the laminar boundary layer. These were operated to produce, through local heating, time-periodic spanwise-phase-varying velocity perturbations. Of primary emphasis in this paper are conditions obtained by the combined forcing of fundamental plane waves with wavenumbers (α, 0) and pairs of subharmonic oblique waves (½α, ± β). The reslults document resonant growth of energy in the subharmonic modes, the formation of staggered lambda vortex patterns with a cross-stream scale commensurate with the seeded ± β condition, and their subsequet transition to turbulence. Complete documentation of the flow field at these various stages is presented using smoke-wire flow visualization and through phase-conditioned hot-wire surveys measuring all three velocity components in three space dimensions.