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Study on free shear layrs control by mians of direct numerical simulations.

直接数值模拟方法控制自由剪切层的研究

基本信息

批准号：
03650154
负责人：
MAEKAWA Hiroshi
金额：
$ 1.41万
依托单位：
The University of Electro-Communications
依托单位国家：
日本
项目类别：
Grant-in-Aid for General Scientific Research (C)
财政年份：
1991
资助国家：
日本
起止时间：
1991 至 1993
项目状态：
已结题

项目摘要

In the present report, the transition mechanism and the structure evolutions in free shear layrs such as wakes, mixing layrs and jets are studied by means of direct numerical simulations. The free shear layrs are perturbed by temporally/spatially developing instability modes obtained from linear stability theory. The incompressible time-dependent Navier-Stoles equations were solved using pade finite difference approximations and a mapped pseudospectral Fourier method/spectral Galerkin method for spatial discretization. The equations were advanced in time using a compact third-order Runge-Kutta scheme. When a fundamental mode is amplified, the development of a stable vortex street in a plane wake appears downstream. When the inlet flow is forced by a fundamental mode and two subharmonics, a vortex street also appearsm, but the shape of the vorticies is distorted. The phase jitter around the fundamental frequency plays a critical role in generateing vorticies of random shape and spacing downstream. The weak back ground noise has little effect on the evolution, the two-dimensional double rollers are the dominant features of the wake. It is also found that the growth of small wavelength oblique modes leads to the breakdown of the spanwise rollers and counter-rotating streamwise vortical structures appear downstream. Furthermore, the effect of compressibility on the growth of instability modes in free shear layrs was investigated. Numerical results reveal that oblique modes are significant in the mixing layrs at the convective Mach number increases. In plane wakes and jets, two-dimensional instability modes show the most amplification rates for higher Mach numbers. Finally, a study of the geometry of flow patterns in numerically simulated compressible mixing layr was carried out using 3-D critical point methodology. Motions corresponding to high rates of dissipation are found to be characterized by a 3-D rate-of-strain topology of types nustable node/saddle/saddle and u

本文采用直接数值模拟的方法，研究了自由剪切层（如尾迹、混合层和射流）中转捩机制和结构演变。由线性稳定性理论得到的时间/空间发展的不稳定模式扰动的自由剪切层。采用Pade有限差分近似和映射拟谱Fourier方法/谱Galerkin方法进行空间离散，求解不可压时变Navier-Stoles方程。方程组采用紧凑的三阶Runge-Kutta格式。当一个基模被放大时，下游出现一个稳定的平面尾流中的涡街。当进口气流受到一个基模和两个次谐波的激励时，也会出现一个涡街，但涡的形状会发生畸变。基频附近的相位抖动在下游产生随机形状和间距的涡旋中起着关键作用。弱背景噪声对尾流的演化影响不大，二维双滚流是尾流的主要特征。小波长斜模态的增长导致展向滚柱的破裂，下游出现反向旋转的流向涡结构。进一步研究了可压缩性对自由剪切层中失稳模态增长的影响。数值结果表明，随着对流马赫数的增加，混合层中的斜模态是显著的。在平面尾流和喷流中，二维不稳定模态在较高马赫数时表现出最大的放大率。最后，用三维临界点方法对数值模拟的可压缩混合层中的流型几何进行了研究。对应于高耗散率的运动被发现具有不稳定节点/鞍/鞍和u型的3-D应变率拓扑结构的特征。