Flow Resistance in Wide Rectangular Channels

Friction coefficients are determined for rectangular channels over a wide range of Reynolds number and a range of width-to-depth ratios of 35 to 1. Comparison with other investigators shows general agreement that the relationship of √f to R_e √f is different from the pipeflow equation,but not on the values of the numerical constants. The influence of width-to-depth ratio on friction factor is examined. It is shown to be complex, probably influenced by both secondary circulation and non-uniformity of shear patterns, in agreement with other work. Two methods of adjusting the channel data to conform to the pipeflow friction factor equation using shape factors are applied. Using these methods, the average divergence between the channel friction factor equation and that applicable to pipeflow can be reduced from 8% to under 2%.