Spatial instability of a swirling flow

The instability of a swirling flow of an inviscidand incompressible fluid is studied on the assumption that the wavenumber k=k_r + ik_i of the disturbance is complex while its frequency ω is real. This implies that the disturbance grows with distance along the axis of the swirling flow, but it does not grow with time. The occurrence of such disturbance is called spatial instability, in contrast to the temporal instability, in which k is a real number and ω=ω_r + iω_i is a complex one. The results show that spatial instability analysis is a useful tool for the comprehensive understanding of the instability behaviours of a swirling flow.     

涡旋流动的空间不稳定性分析

本文研究无粘、不可压缩流体的涡旋流动的空间不稳定性,假定扰动波的波数k=k_r+ik_i是一复数,而它的频率ω为一给定的实数。这一假定意味着扰动沿涡旋流动的轴向随距离的增长而增长,但不随时间而增长。这种扰动的产生称之为空间不稳定性;与之相对应的是时间不稳定性,扰动波的波数k为一实数,而频率ω=ω_r+iω_i是一复数。本文的结果表明空间不稳定性分析是全面认识涡旋流动不稳定性的一种有用的工具。     

应用于非惯性系湍流模拟的扩展内禀旋转张量

研究扩展内禀旋转张量在非惯性系湍流模拟中的作用,特别是对代数Reynolds应力湍流模式(如非线性K-ε模式)的重要性．为此,采用几个近年来发展的非线性K-ε湍流模式模拟旋转坐标系下均匀剪切湍流,并且和大涡模拟的结果进行比较．计算结果和分析表明,需要发展更先进的非线性K-ε模式从而更好地描述非惯性系下的复杂湍流．