The distribution of velocity in an open channel of rectangular section

The particulars given in this short note have been obtained during the calibration of a hydraulic channel recently completed at the University of Liverpool. The immediate object of the calibration was to explore the central portion of the stream and to obtain the limits of the area of cross-section over which the velocity of flow parallel to the channel might be regarded as sensibly uniform. Measurements of velocity were made at a range of levels and also at a series of verticals in the same transverse plane. As the work proceeded, from the nature of the observations, it seemed worth while taking the opportunity of mapping completely the contours of constant axial velocity and so to supplement the somewhat limited experimental data previously obtained under laboratory conditions for the flow in a uniform channel.The Apparatus .—Water was circulated in a closed circuit by a speed-regulated shunt-wound motor driving an axial flow pump which drew water from the downstream end of an open steel channel of rectangular cross-section, and delivered it through a pipe to the upstream end of the channel. The arrangement of the channel is illustrated by the plan, elevation and sections in fig. 1. Its length between the end plates is 66 feet; everywhere its transverse section is a rectangle. It is of the uniform width of 5 feet for 44 feet at the downstream end. At the inlet end the channel is bulbous in plan, attaining a maximum width of 7 feet, contracting by gentle curves of 41 feet radius into the bulbous end through a pipe subdivided by axial baffles L in two vertical planes, transverse and longitudinal, in order to destroy as far as practicable the "spin" of the water as it comes round the bend to enter the channel. The longitudinal division was adjusted so as to secure equal volumes of flow in each half of the channel.