Velocities Above Rough Bed in Oscillatory Flow

by John F.A. Sleath, Sr. Asst. in Res.; Dept. of Engrg., Univ. of Cambridge, Cambridge, England, U.K.,

Serial Information: Journal of the Waterways, Harbors and Coastal Engineering Division, 1974, Vol. 100, Issue 4, Pg. 287-304

Document Type: Journal Paper


The fluid velocities close to a two-dimensional rough bed are calculated for laminar oscillatory flow, similar to that produced by waves near the seabed. At low Reynolds numbers a small-perturbation procedure is used and at high Reynolds numbers the equations of motion are solved numerically, using a finite-difference approximation. The numerical solution indicates that the flow remains laminar up to much higher Reynolds numbers than has previously been supposed and this conclusion is confirmed by hot-wire anemometer measurements. Comparison of the computed velocity profile with measurements by Kalkanis suggests that the mean velocities may still be well represented by the numerical solution even when the flow does become turbulent. The solution involves no experimentally-determined constants and applies to situations of practical importance, and also to flow over flat beds of sand provided an appropriate definition of roughness length is used.

Subject Headings: Flow measurement | Reynolds number | Fluid velocity | River and stream beds | Oscillations | Oscillatory flow | Fluid flow | Two-dimensional flow

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