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Generation and Growth of Coherent Structures and Turbulent Elementary Vortices

相干结构和湍流基本涡旋的产生和增长

基本信息

批准号：
12125203
负责人：
NISHIOKA Michio
金额：
$ 44.22万
依托单位：
Osaka Prefecture University
依托单位国家：
日本
项目类别：
Grant-in-Aid for Scientific Research on Priority Areas
财政年份：
2000
资助国家：
日本
起止时间：
2000 至 2002
项目状态：
已结题

项目摘要

The main objectives of the present studies are to clarify the generation and growth process of large-scale coherent vortical structures and their subsequent breakdown into small-scale elementary vortices and then to develop elemental manipulation methods for turbulence control. In the study on the wall turbulence mechanism the so-called near-wall streaks are experimentally examined to find that the algebraic growth mechanism is responsible for their occurrence in a laminar wall layer excited by high-intensity random turbulence, and that their instability gives rise to a train of quasi-streamwise vortices of alternating sign and further that the sinuous streak instability can maintain the same low speed streaks of 100 wall units as in fully developed wall turbulence. In the study on the vortical structures in a uniformly sheared turbulence in a rotating system, direct numerical simulations demonstrate that owing to the Coriolis force high-vorticity blobs easily develop to local vortex layers, which soon evolve into tubular vortices. The tubular vortices are intensified and maintained long under a combined effect of the Coriolis force and the vortex-induced pressure gradient. In the study on the turbulence manipulation our research efforts are focused onto the supersonic mixing enhancement using streamwise vortices. The instability and the mixing capability of the so-called hollow vortex are examined theoretically and numerically. Experimentally it is found that the supersonic streamwise vortices can be excited by high-frequency disturbances due to cavity-flow oscillations to have energetic fluctuations in the Kolmogorov's -5/3 power law frequency range for the vortex Reynolds numbers beyond about 10^4. In the study on the vorticity manipulation using pile fabrics our model describing their aerodynamic effect is verified through experimental and numerical efforts in particular for the case of TS waves over the pile fabric wall boundary layer.

本研究的主要目标是澄清大尺度相干涡结构的产生和增长过程，以及随后分解成小尺度的基本涡，然后发展用于湍流控制的基本操作方法。在壁面湍流机制的研究中，对所谓的近壁条纹进行了实验研究，发现在高强度随机湍流激励下的层流壁面层中，代数增长机制是其产生的原因，他们的不稳定性导致了一系列准交替符号的流向涡，并进一步指出，蜿蜒条纹不稳定性可以保持相同的低速条纹的100壁单位，因为在充分发展的壁急流.在对旋转系统中均匀剪切湍流的涡结构的研究中，直接数值模拟表明，由于科氏力的作用，高涡度的涡团容易发展成局部涡层，并很快演变成管状涡。在科里奥利力和涡激压力梯度的共同作用下，管涡得到强化并维持较长时间。在湍流操纵的研究中，我们的研究工作集中在利用流向涡增强超声速混合。本文从理论上和数值上研究了所谓的空心涡的不稳定性和混合能力。实验上发现，当涡雷诺数超过10^4时，由于空腔流振荡引起的高频扰动可以激发超音速流向涡，使其在柯尔莫哥洛夫-5/3幂律频率范围内产生能量波动。在涡量操纵的研究中，我们的模型描述了他们的空气动力学效应，通过实验和数值计算的努力，特别是在TS波的情况下，在毛绒织物壁边界层进行了验证。