Developing disturbances in shear
Developing disturbances in shear
复制标题
剪切扰动的发展
DOI：
10.1175/1520-0469(1987)044
复制
发表时间：
1987
影响因子：
3.1
通讯作者：
B. Farrell
中科院分区：
文献类型：
--
作者：
B. Farrell
传统上认为剪切流中扰动的产生和发展是由于流动的线性模态不稳定性。最近关于初值问题的研究表明，至少在快速发展的情况下，扰动的非模态增长可能具有同等的重要性，甚至可能更重要。在不支持不稳定性的模型问题和具有实际Ekman阻尼的斜压流动中，指数模态的增长率为零或负，已经给出了稳健增长的例子。这样的例子把注意力集中在被配置为利用平均流能量的扰动上。这里给出了这些有利配置扰动的关键检查，利用简单的常数自由剪切正压模型，允许构建精确的二维孤立波包解。
Abstract The origin and growth to moderate amplitude of disturbances in shear flow has been traditionally ascribed to the linear modal instability of the flow. Recent work on initial value problems has suggested that nonmodal growth of perturbations may be of equal and perhaps greater importance, at least in cases of rapid development. Examples of robust growth in model problems which support no instabilities and in baroclinic flows with realistic Ekman damping for which the exponential modes have zero or negative growth rates have been shown. Such examples have focused attention on the perturbations which are configured to tap the energy of mean flows. Here a critical examination of these favorably configured perturbations is given, making use of the simple constant free shear barotropic model which allows construction of exact two-dimensional isolated wave packet solutions.