Shallow Laminar Flows over Rough Granular Surfaces

by Harry O. Phelps, Prof.; Dept. of Civ. Engrg., Univ. of West Indies, St. Augustine, Trinidad, West Indies,

Serial Information: Journal of the Hydraulics Division, 1975, Vol. 101, Issue 3, Pg. 367-384

Document Type: Journal Paper


Several investigations have established that at high values of relative roughness mean depths of liquid in laminar shear flow over rough surfaces are greater than the corresponding depths on a smooth surface. In this investigation the nature of the flow field in the vicinity of isolated roughness elements fixed to a smooth base is demonstrated using a flow visualization technique. Velocity profiles measured with an optical velocity meter are shown to be governed by the Nusselt equation, but surface velocity is a function of relative roughness and is less than the corresponding value for a smooth surface. An analytical model is proposed to explain an empirical relationship between friction coefficient, relative roughness, and Reynolds number. The equation developed is used to calculate the product of the coefficient of drag of a sphere resting on a plane surface and the tip Reynolds number and also to demonstrate the influence of velocity distribution on the drag coefficient.

Subject Headings: Velocity profile | Laminar flow | Granular materials | Hydraulic roughness | Overland flow | Shear flow | Field tests | Flow visualization

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