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第167行： − 湍流扩散通常用湍流扩散系数来描述。这种湍流扩散系数是类比于分子扩散系数，从唯象的意义上定义的，但它取决于流动条件，而不是流体本身的性质，没有真正的物理意义。此外，湍流扩散率概念假定了湍流通量和平均变量梯度之间的本构关系，类似于分子输运中存在的通量和梯度之间的关系。在最好的情况下，这个假设只是一个近似值。然而，湍流扩散系数是定量分析湍流流动的最简单的方法，许多模型已被假定用来计算它。例如，在像海洋这样的大型水体中，这个系数可以用理查森的四分之三次方定律找到，并受随机游动原理支配。在河流和大洋流中，扩散系数是通过埃尔德公式的变化得到的。+
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* Smoke rising from a [[cigarette]]. For the first few centimeters, the smoke is [[Laminar flow|laminar]]. The smoke [[Plume (fluid dynamics)|plume]] becomes turbulent as its [[Reynolds number]] increases with increases in flow velocity and characteristic lengthscale.
* Smoke rising from a [[cigarette]]. For the first few centimeters, the smoke is [[Laminar flow|laminar]]. The smoke [[Plume (fluid dynamics)|plume]] becomes turbulent as its [[Reynolds number]] increases with increases in flow velocity and characteristic lengthscale.
烟雾从一支香烟上升起。最开始的几厘米，烟雾是层流。'''<font color="#ff8000"> 雷诺数Reynolds number </font>'''随着流速和特征长度增加时，飘起来的烟变成了湍流。
* 烟雾从一支香烟上升起。最开始的几厘米，烟雾是层流。'''<font color="#ff8000"> 雷诺数Reynolds number </font>'''随着流速和特征长度增加时，飘起来的烟变成了湍流。
Turbulent diffusion is usually described by a turbulent diffusion coefficient. This turbulent diffusion coefficient is defined in a phenomenological sense, by analogy with the molecular diffusivities, but it does not have a true physical meaning, being dependent on the flow conditions, and not a property of the fluid itself. In addition, the turbulent diffusivity concept assumes a constitutive relation between a turbulent flux and the gradient of a mean variable similar to the relation between flux and gradient that exists for molecular transport. In the best case, this assumption is only an approximation. Nevertheless, the turbulent diffusivity is the simplest approach for quantitative analysis of turbulent flows, and many models have been postulated to calculate it. For instance, in large bodies of water like oceans this coefficient can be found using Richardson's four-third power law and is governed by the random walk principle. In rivers and large ocean currents, the diffusion coefficient is given by variations of Elder's formula.
Turbulent diffusion is usually described by a turbulent diffusion coefficient. This turbulent diffusion coefficient is defined in a phenomenological sense, by analogy with the molecular diffusivities, but it does not have a true physical meaning, being dependent on the flow conditions, and not a property of the fluid itself. In addition, the turbulent diffusivity concept assumes a constitutive relation between a turbulent flux and the gradient of a mean variable similar to the relation between flux and gradient that exists for molecular transport. In the best case, this assumption is only an approximation. Nevertheless, the turbulent diffusivity is the simplest approach for quantitative analysis of turbulent flows, and many models have been postulated to calculate it. For instance, in large bodies of water like oceans this coefficient can be found using Richardson's four-third power law and is governed by the random walk principle. In rivers and large ocean currents, the diffusion coefficient is given by variations of Elder's formula.
湍流扩散通常用湍流扩散系数来描述。这种湍流扩散系数是类比于分子扩散系数，从唯象的意义上定义的，但它取决于流动条件，而不是流体本身的性质，所以没有真正的物理意义。此外，湍流扩散率概念假定了湍流通量和平均变量梯度之间的本构关系，类似于分子输运中存在的通量和梯度之间的关系。在最好的情况下，这个假设只是一个近似值。然而，湍流扩散系数是定量分析湍流流动的最简单的方法，许多模型已被假定用来计算它。例如，在像海洋这样的大型水体中，这个系数可以用理查森的四分之三次方定律找到，并受随机游动原理支配。在河流和大洋流中，扩散系数是通过埃尔德公式的变化得到的。