Free Surface Flow In A Channel Of Large Relative Roughness

Abstract

Characteristics of free surface flow over a bed consisting of hemispherical roughness elements have been studied experimentally. Theoretical bottom of the channel has been located at a distance of 35% of the diameter below the tops of hemispheres. Usual logarithmic laws are valid for velocity distribution and friction factor as long as flow depth is large relative to roughness height. Equivalent sand roughness of the bottom is equal to 2.5 times the diameter of hemispheres. At large values of relative roughness, on the other hand, lower velocities are observed than the logarithmic law predicts, and friction factor also increases by as much as 50%. Intensity of turbulence fluctuations decreases with the increase of relative roughness. Probability density function of velocity fluctuations near the rough bed tends away from the normal distribution.