Investigation of the Friction Coefficient in Smooth Open Channel Flows


Abstract: In practical engineering, the friction coefficient formulations developed for circular pipes are usually assumed to be valid for open channels and used in derivation of mathematical formulation. However, with the advent of more accurate measurement devices, it is now clear that such formulations cannot be used in open channels without modifications. The phenomena such as free surface, different wet surfaces with irregular shear stresses and secondary flows, make open channel flows more complicated than circular pipe flows. A new formulation for the friction coefficient is developed depending on the Reynolds Number (Re) and W/h, which is the ratio of channel width to its height. It is found that there is a 10 \% difference in the friction coefficient in circular pipe flow and open channel flow under the same conditions. The new correlation agrees satisfactorily with those in the literature. The relation between $\lambda$ and $Re$ in circular pipe flow is found to be deviate in open channel flows. In this research a formulation similar to the Blasius equation is proposed for rectangular channels.

Keywords: Open channel, energy loss, friction factor.

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