Turbulence Measurements above Sharp-crested Gravel Bedforms

This paper primarily presents velocities, Reynolds stresses and turbulence intensities of flow over a series of two-dimensional asymmetric sharp-crested, gravel bedforms. The bedforms have a mean wavelength of 0.96 m, a mean height of 0.08 m, and a width of 0.4 m (equal to the flume width) and a lee slope of 28. The results show that extrapolating spatially-averaged log-law velocity profiles provided the best estimate of bed shear stress for bedforms. Maximum values of the root-mean-squared velocity over the sharp-crested gravel bedforms were located farther away from the bed when compared to those for sand dunes. The Reynolds stresses were zero or negative near the water surface over sand dunes, whilst they were positive over sharp-crested gravel bedforms. The length of the separation zone of gravel dunes was less than that for sand dunes, showing a faster reattachment over a gravel bed in comparison to that of a sand bed. Quadrant analysis showed that near the bed the contributions of sweep and ejection events changed with an oscillatory pattern along the sharp-crested gravel bedforms, however, such a pattern was not observed close to the water surface.

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