Abstract
A comparison is made of the alternating and direct flow of air near the mouths of tubes of various sections, by traversal of a hot-wire anemometer across the tube. After a correction for the use of the hot wire in the neighbourhood of the walls of the tubes has been made, the theoretical and observed gradients of mean velocity across the sections are compared. In the alternating flow a peak of high average velocity is found near the walls of the pipe, but in one-way flow this annular peak is absent, the velocity falling continuously from the centre of the tube to within a short distance of the walls according to the law v = ayq, where q varies from 1/2 for stream-line flow up to 1/7 for turbulent flow. The existence of a layer of laminar flow close to the walls, when the main body of air is in turbulent motion, is demonstrated.