Civil Engineering, Urmia University
Water flow in open channels is always subject to the resistance to flow and energy dissipation. For design purposes, one of the needed variables is the hydraulic resistance coefficient. For this mean, the influence of cross-sectional shape together with secondary flow cells and lateral distribution of true boundary shear stress have not yet been fully explored. This paper surveys the number of research work carried out last few decades and highlights effect of cross sectional shape on resistance to flow. A particular emphasis has been focused on a certain v-shaped bottom channel with vertical walls, and its resistance coefficient evaluation. The experimental results show that albeit the channel has a smooth boundary, but the resistance coefficients cannot be applied for this channel. Thedifference may be arisen by the effect of cross sectional shape. A Karman-Prandtl smooth pipe flow type friction formula was then developed for this particular channel shape. It can also be seen that the Darcy-Weisbach friction factor, f, is more sensitive than that of the Manning n.