Winter D C, Nerem R M
Ann Biomed Eng. 1984;12(4):357-69. doi: 10.1007/BF02407780.
Turbulence during pulsatile flow has been suggested as a possible mechanism to enhance the transport of gases during high-frequency ventilation. Experimental studies on oscillatory flow in straight, circular tubes have identified three types of flow: (a) laminar; (b) conditionally turbulent, in which high-frequency disturbances occur during the decelerating phase of the flow cycle but relaminarize by the beginning of the subsequent accelerating phase; and (c) fully turbulent flow, in which disturbances occur throughout the flow cycle. Fully turbulent flow has been observed only when a mean flow is present, and only laminar or conditionally turbulent flow has been observed for purely oscillatory flow. A critical Reynolds number based on the Stokes layer can be defined, and transition Reynolds numbers between 400 and 550 have been experimentally determined for purely oscillatory flow in a circular tube, although lower values are expected for physiological flows. There are some indications that the structure of oscillating turbulent flow is similar to steady turbulent flow, and preliminary work in our laboratory shows that the spectral content of flows during high-frequency ventilation is similar to that in steady turbulent flow.
脉动流期间的湍流被认为是高频通气时增强气体传输的一种可能机制。对直管中振荡流的实验研究确定了三种流动类型：(a)层流；(b)条件湍流，即在流动周期的减速阶段出现高频扰动，但在随后加速阶段开始时重新层流化；(c)完全湍流，即在整个流动周期中都出现扰动。仅当存在平均流时才观察到完全湍流，而对于纯振荡流仅观察到层流或条件湍流。可以定义基于斯托克斯层的临界雷诺数，对于圆管中的纯振荡流，实验确定的过渡雷诺数在400至550之间，尽管生理流动预期的值更低。有一些迹象表明振荡湍流的结构与稳定湍流相似，并且我们实验室的初步工作表明高频通气期间流动的频谱内容与稳定湍流中的相似。
