[理学]第7章 粘性流体动力学_5.pdf

第七章 粘性流体运动 湍流运动基本方程的建立 What is the turbulence? Nobody knows. According to an apocryphal story, Werner Heisenberg was asked what he would ask God, given the opportunity. His reply was: When I meet God, I am going to ask him two questions: Why relativity? And why turbulence? I really believe he will have an answer for the first .” A similar witticism has been attributed to Horace Lamb (who had published a noted text book on Hydrodynamics)—his choice being quantum electrodynamics (instead of relativity) and turbulence. Lamb was quoted as saying in a speech to the British Association for the Advancement of Science, I am an old man now, and when I die and go to heaven there are two matters on which I hope for enlightenment. One is quantum electrodynamics, and the other is the turbulent motion of fluids . And about theformer I am rather optimistic.” /wiki/Turbulence 第七章 粘性流体运动 湍流运动基本方程的建立 梵高和达芬奇分别以湍流为题材创作的两幅世界名画 Vincent Van Gogh Leonard de Vinci 第七章 粘性流体运动 湍流运动基本方程的建立 湍流的一些基本特征  Irregularity (不规则性): This is why turbulence problems are always treated statistically rather than deterministically. Turbulent flow is always chaotic but not all chaotic flows are turbulent.  Diffusivity(扩散性): Turbulence is highly associated with rapid mixing. The system becomes a homogeneous system. A chaotic flow is never turbulent if it does not diffuse.  Rotationality(有旋性): Characterized by a strong three-dimensional vortex generation mechanism known as vortex stretching. This is why turbulence is always rotational and three dimensional.  Dissipation(耗散性): Turbulence dissipates rapidly as the kinetic energy is converted into internal energy by viscous shear stress 第七章 粘性流体运动 湍流运动基本方程的建立 湍流的一些基本特征  Energy cascade(多尺度的能量传递和叠加): Turbulence is made of an entire hierarchy of eddies over a