ANALYSYS OF STRUCTURE.MODELLING AND CONTROL IN A WALL TURBULENCE BY USING LES AND DNS

本文利用瞬态大涡模拟数据库和三维计算机图形对壁面湍流中条纹及其周围场的产生进行了讨论，观察到在条纹周围的空间中间歇地出现雷诺剪应力的产生、扩散、再畸变等现象，雷诺切应力出现在近壁区湍流的产生和事件产生负扩散的地方。在模拟观点上，指出速度-压力梯度项不应分裂为压力扩散项和压力-应变项。此外，对于近壁区的再生过程，发现准流向涡在其自身的上游产生新的涡。这些涡旋是反向旋转的，并构成一种链结构。再生是由于壁面法向涡的倾斜和自身的拉伸， ...更多信息 为了研究湍流结构，需要研究非均匀流动。然后，我们测量了波浪形通道流中的流，即在一侧具有平板壁而在另一侧具有波浪形壁的通道。实验数据，即，湍流强度、湍流应力和偏斜度反映了压力梯度对流场的影响。以近轴对称或螺旋扰动为初始条件，计算了湍流的时间发展过程。因此，在螺旋微扰的情况下，结构开始出现更早，并保持更长的寿命相干结构比在近轴对称微扰的情况下。本文用数值方法论证了喷流控制湍流和气动声学的可能性，提出了用DNS分析声源分布的方案和高分辨率声源分析的可能性，论证了通过观察流场的大尺度结构来估计方柱表面声源的方法是值得注意的。少

Discussions are presented concering the generation of streaks and fields around them in the wall turbulence using an instaneneoius LES data-base by means of a three dimensional computer graphics.As a result, it is observed that the phenomena of prpduction, diffusion, redistoribution of Reynolds shear stress appear intermittently in space around streaks, and that Reynolds shear stress is found at places where production and events of turbulence at near wall region produce negative diffusion. Also in the modelling view points, it is shown that velocity-pressure gradient term should not be splitted into pressure diffusion term and pressure-strain one. Furthermore as for regeneration process at near wall region, it is found that quasistreamwise vortices generate new vortices upwardstream of themselves. These vortices are counter-rotating and constitute a sort of chain structure. Regeneration is due to tilting of wall normal vortices and to stretching of itself.To be confirm the generality … More of turbulence structure, it is needed to investigate inhomogeneous flow. Then, we measured a flow in a wavy channel flow, namely channel having a flat plate wall on one side and wavy in the other side. Experimented data, i.e., turbulence intencity, turbulence stresses and skeweness, shows the effect of pressure gradient in the flow field.DNS code was manufactured for a round jet. As initial conditions nearly axi-symmetric or herical petrubation were assumed and calculations of temporally developing process of turbulent flow were conducted. As a result, in the case of helical peturbation, structure begins to appear earlier and maintains longer-lived coherent structure than in the nearly axi-symmetric peturabation case. It was demonstorated numerically the possibility of turbulence control and aeroacoustics control of jets.The scheme of analysys of sound source distribution and the possibilty of high resolution analysys of sound souce were also presented by using DNS.It is demonstrated that estimation of the sound source on the surface of a square cylinder by observing the large-scale structure of flow should be careful. Less