Study of the Structure of Wall-Turbulence and Turbulence Noise

这项研究计划涉及几个主题。对于相互作用问题，在一定人工条件下的模型模拟表明，光滑壁面上的近壁层具有显著的自持能力和普适性，不依赖于外层的特性。墙体上的粗糙度破坏了这一特性，并使外层的特性几乎占据了整个层。具有波浪壁的槽道流动证实了这一结论，并对固体颗粒对外层的调制特性进行了研究。新发明的跟踪运动中粒子的技术效果令人满意，揭示了湍流动力学中可能适用于湍流控制的重要方面。在没有使用任何模型的情况下，模拟了壁面湍流发出的噪声。声源场和伴生声场以时间推进的方式连续计算。事实证明，并不是所有的涡旋都会产生声音，但某些特定的涡旋事件只会产生噪音。作为提高噪声计算可靠性的基础，对自由圆喷流进行了高分辨率的数值模拟。用整体稳定性分析的方法，从涡旋结构产生的机制出发，对产生噪声最主要的射流近场进行了研究。

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.