论文标题
非线性输入/输出分析：应用于边界层过渡
Non-linear input/output analysis: application to boundary layer transition
论文作者
论文摘要
我们通过使用谐波平衡方法考虑频域中的有限数量的谐波，扩展了线性输入/输出/输出（分解）分析，以考虑到非线性三合会相互作用。使用基于梯度的上升算法计算出最大化阻力的强迫机制。通过在分析中包括非线性，提出的频域框架可以确定层状扰动过渡的最坏情况。我们通过考虑由一些有限振幅的最佳强迫模式触发的三维跨度 - 周期性扰动来演示扁平板边界层上的框架。考虑了两种类型的体积强迫，另一种对应于单个频率/跨度波 - 波对，以及一个多谐波，其中还添加了谐波频率和波数。根据强迫策略，我们恢复了与K型和H型机制相关的一系列过渡方案，包括斜和tollmien-Schlichting波，条纹及其分解。我们表明，非线性通过将线性机理和较高扰动谐波之间的能量结合和重新分布在优化生长中起着至关重要的作用。由于频率和波数范围非常有限，通过发夹和准式交错涡流的产生和分解，计算似乎达到了湍流状态的早期阶段。
We extend linear input/output (resolvent) analysis to take into account nonlinear triadic interactions by considering a finite number of harmonics in the frequency domain using the harmonic balance method. Forcing mechanisms that maximize the drag are calculated using a gradient-based ascent algorithm. By including nonlinearity in the analysis, the proposed frequency-domain framework identifies the worst-case disturbances for laminar-turbulent transition. We demonstrate the framework on a flat-plate boundary layer by considering three-dimensional spanwise-periodic perturbations triggered by a few optimal forcing modes of finite amplitude. Two types of volumetric forcing are considered, one corresponding to a single frequency/spanwise-wavenumber pair, and a multi-harmonic where a harmonic frequency and wavenumber are also added. Depending on the forcing strategy, we recover a range of transition scenarios associated with K-type and H-type mechanisms, including oblique and Tollmien-Schlichting waves, streaks and their breakdown. We show that nonlinearity plays a critical role in optimizing growth by combining and redistributing energy between the linear mechanisms and the higher perturbation harmonics. With a very limited range of frequencies and wavenumbers, the calculations appear to reach the early stages of the turbulent regime through the generation and breakdown of hairpin and quasi-streamwise staggered vortices.
