ABSTRACT
The results of some laboratory experiments are reported concerning the distribution of boundary shear stresses in smooth open channels and closed conduits with a rectangular cross section. Perturbations in these distributions are explained in terms of secondary flows and the formation of pairs of contra-rotating cells adjacent to the long side of the rectangle. The proportion of the total shear force which acts on the channel or duct walls is shown to vary systematically with aspect ratio, but not in accordance to the ratio of wall to overall perimeter lengths. Equations are presented for the variation of the wall shear force, mean wall and bed shear stresses, and centreline bed shear stress with aspect ratio. The differences and similarities between open channel and closed conduit flows at comparable aspect ratios are noted.
