Spacetime dynamics of bed forms due to turbulence around submerged bridge piers

Abstract

This work presents a study of spatiotemporal changes of scour-holes around sand embedded submerged circular and non-circular cylinders with associated turbulence properties and aims at analyzing the contribution of each quadrant event to the Reynolds shear stress. Experiments were carried out using submerged circular, elliptical, square and triangular cylinders of same length having flow-facing sides as the cylinder diameter with a common submergence ratio of 0.6. It is evident that upstream scour depth was maximum for the circular cylinder and minimum for the elliptical one. Interestingly, side-wise scouring rate was significant for elliptical cylinder. The maximum deposition region was formed at the downstream of the triangular cylinder case; and for the square cylinder, interestingly quite largest sediment accumulations occurred at the two sides about the centerline. The bed elevation spectra for all cases in downstream scour and deposition region showed comparatively higher spectral slopes, where positive bed slopes were generated except for the square cylinder case. In the near-bed region of upstream scour hole, the occurrence of probabilities were higher for sweeping events and it was less for the elliptical cylinder, where the bed was minimum negatively sloped, compared to other cylinders. In the downstream scoured location of the elliptical cylinder, where comparatively lower bed elevation was formed and the bed was negatively sloped, mostly the ejections were the occurring events near the bed region. However, for the other three cases with positive bed slopes, sweeping events were the dominating in near-bed region.