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Large cultures of microscopic, unicellular algae have been proposed as a means of maintaining a life‐supporting atmosphere in a closed, manned system. To achieve vigorous growth of the algal culture it is necessary to subject individual algae alternately to short periods of high intensity light and darkness. One of the means suggested for obtaining a favorable light–dark sequence for photosynthesis is to cause turbulence in a closed channel on which light is incident. Since light is rapidly attenuated in a dense suspension, there will be illuminated regions adjacent to the channel walls and a dark central core. The random motions of turbulence normal to the direction of flow would move the algae alternately from the illuminated regions to the dark region and back again. This paper indicates a method for analyzing the motion of algae into and out of the illuminated region of a channel formed by flat, parallel, transparent plates, with light incident on the plates. Matching of a probability model with a diffusion model makes it possible to estimate the light–dark sequence which could be achieved by turbulence. The results indicate that favorable sequences by this mechanism are unlikely.

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Fundamental turbulent flow techniques are used to examine the annular fluid flow occurring in an idealized model of a high speed ground transportation system. The model consists of a smooth cylindrical train moving in an infinitely long tunnel, creating an annular gap with one wall in motion. The developing, and the fully developed, flow regions are separately analyzed by using fundamental relations of turbulent flow and Von Karman’s similarity hypothesis. The relevant equations are developed and numerical solution procedures presented. Limited sample calculations show good agreement with existing empirical and experimental results.