报 告 人： 吴雪松 教授
报告题目：Instability waves/coherent structures in transitional/turbulent free shear flows:nonlinear evolution and acoustic radiation
报告时间：2019年9月27日（周五）10:30
报告地点：土木楼212报告厅
邀 请 人： 南非科学院院士、力学技术研究院院长、首席科学家 孙博华教授
报告摘要：
Free shear flows, such as mixing layers, jets and wakes, are inviscidly unstable due to their inflectional velocity profiles. Instability modes, which are usually excited by external perturbations, amplify on the shear flow, leading to vortex roll-up and randomization in the nonlinear stage. Interestingly, in turbulent state free shear flows exhibit a high de-gree of order, characterised by the prevalent presence of the so-called coherent structures,the most striking of which are ’Brown-Roshko rollers’. There structures bear remark-able resemblance to instability modes, raising the prospect that their dynamics might be understood and predicted by instability theory.
Instability waves and coherent structures are known to be dynamically significant for en-trainment and mixing, noise generation as well as for turbulence modelling. In this talk,I will present a unified nonlinear critical-layer theory to describe the development of in-stability modes/coherent strictures on transitional/turbulent free shear layers. The effects of non-parallelism and small-scale fluctuations are accounted for. The theory predicts nonlinear saturation, randomisation through a generalized side-band instability mecha-nism and formation of ’Brown-Roshko rollers’. Furthermore, by analyzing the far-field asymptotic behaviour of the coherent structures, we are able to explain and predict, on the first-principle basis, how coherent structures radiate sound.
报告人简介：
吴雪松， 1985 毕业于复旦大学。同年入天津大学, 在周恒教授指导下开始从事流动稳定性研究。1988 年入帝国学院数学系,于 1992 年获得博士学位。自 1993 起，任帝国学院数学系讲师、副教授 (Reader)、应用数学教授, 天津大学长江特聘教授。先后作为顾问或访问科学家/教授，在 NASA Glenn、 NASA Langley、NASA Ames 研究中心以及斯坦福大学、普林斯顿大学和法国法国巴黎高等工程学校进行合作研究。2004 年入选‘海外杰出青年’。2010 年 8 月起天津大学“国家千人计划教授“。研究领域为流动稳定性和层流-湍流转捩，气动声学和燃烧学理论。主要论文在 J. Fluid Mechanics, Physics of Fluids 上发表。美国航空航天学会通讯会士（Associate Fellow of AIAA）;“南开大学天津大学刘徽应用数学中心“学术委员会委员。（1）英国伦敦皇家学会哲学期刊（Philosophical Transaction of the Royal Society of London）编委；（2）国际应用力学期刊 (International Journal of Applied Mechanics)编委；（3）应用数学和力学期刊英文版 (Journal of Applied Mathematics and Mechanics, English Edition) 编辑；（4）期刊《气体物理》编委.
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