Experimental Study of the Hydrodynamic Forces on a Bed Element in an open Channel with a Backward-Facing Step
✍ Scribed by Wang Xingkui; H.L. Fontijn
- Publisher
- Elsevier Science
- Year
- 1993
- Tongue
- English
- Weight
- 577 KB
- Volume
- 7
- Category
- Article
- ISSN
- 0889-9746
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✦ Synopsis
The instantaneous drag and lift force on an individual bed element forming part of a closely packed cover layer and the flow velocities above it were measured in an open channel with a backward-facing step. Mean values and fluctuation characteristics have been determined at six sections downstream of the step, along a distance of about 23 step heights. The structure of the flow field appears to be consistent with those found in the literature for comparable situations. The mean drag force and the square of the mean longitudinal flow velocity show a mainly linear relationship, provided the velocity is determined at (0-15 D) above the relevant bed element, (D) being its mean diameter. For the lift force this only applies from 18 step heights downstream of the step, where the flow is almost uniform. At a downstream distance of 14 and more step heights, the intensities of the force fluctuations have at least the same order of magnitude as the mean forces. The probability density functions of the drag and lift force are not Gaussian. Of the "energy" of both the force components and the longitudinal flow velocity (90 %) is concentrated in the low frequency range.