Study of the Structure of Wall-Turbulence and Turbulence Noise

在这个研究计划中，有几个课题受到关注.对于近壁层与壁面的相互作用问题，在一定的人工条件下进行的模型模拟表明，光滑壁面上的近壁层具有显著的自维持能力和普遍性，而与壁面外层的性质无关。壁面粗糙度破坏了这一特性，使几乎整个层被外层的特性所占据。本文还以波浪壁面槽道流动为例验证了这一结论，并研究了固体颗粒对槽道外层流动特性的影响。一种新的追踪运动中颗粒的技术，在不使用任何模型的情况下，成功地揭示了湍流动力学的一些重要方面，这些方面可能适用于湍流控制。采用时间推进法连续计算了声源场和伴随声场。事实证明，并非所有的涡流都产生声音，但某些特定的涡流事件只会产生噪音。作为提高噪声计算可靠性的基础，对自由圆射流进行了高分辨率的数值模拟。本文还通过全局稳定性分析研究了产生噪声的主要原因--射流近场涡结构的产生机理。

Several subjects are in concern in this research program. Namely, interaction between near-wall layer up to several tens in wall unit and outer layer, modulation of outer layer which may contribute to drag reduction and turbulence noise emitted from wall turbulence.As for the interaction problem, model simulations under certain artificial conditions revealed that near-wall layer over smooth wall has remarkable self-sustenance ability and universality, independent on the property of outer layer. Roughness on the wall has been found to destruct this property and makes almost whole layer occupied by the property of outer layer. Channel flow having wavy wall has confirmed the conclusion.Outer layer property modulated by solid particles has been investigated as well. New technique invented to trace particles in motion works satisfactorily and revealed important aspects of turbulence dynamics that may be applicable for turbulence control.Noise emitted from turbulence over a wall has been simulated without using any models. Source field and accompanying acoustic field have been consecutively calculated in time-marching manner. It turned out that not all the vortices generate sound but certain particular events of vortex only contribute for noise generation. As the basis of enhancing reliability of noise calculation, free round jet has been simulated with high resolution. Near field of a jet which is most responsible for noise generation has been also investigated with respect to the mechanism of birth of vortical structure, by global stability analysis.