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 flowfacing 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.

Geometry of obstacle marks at instream boulders—integration of laboratory investigations and field observations

“…Although recent studies have examined the evolution of scourhole geometry for different types of obstacles and sediment sizes, by utilizing a range of measurement methods (Bouratsis et al, 2013(Bouratsis et al, , 2017Diab et al, 2010;Link et al, 2008;Poggi & Kudryavtseva, 2019;Rogers et al, 2020;Sarkar et al, 2015), these studies have focused on d s , while ignoring w s and l s . Nevertheless, there is general agreement that the geometry of frontal scour holes can be approximated as an inverted frustum cone with an elliptical shape in plan view (l s < w s ) ( Figure 1a) (Mia & Nago, 2003), whereas the longitudinal shape (i.e.…”

Prediction of plane‐wise turbulent events to the Reynolds stress in a flow over scour‐bed

“…It hitherto remains unclear whether the statistical properties of all three covariance terms, , , and are equally important over the scour hole structure or there is one leading shear stress plane out of the three involving the bursting events over and within the scour geometry to be investigated. The development of scour mark around the obstacle on the sandy bed under the action of turbulent flow has the potential to be useful to researchers or scientists who study the dynamics of pipelines and short cylinders placed on riverbeds, seabeds, and coastal areas (Sumer & Fredsoe, , ; Voropayev, Cense, McEachern, Boyer, & Fernando, ; Voropayev, Testik, Fernando, & Boyer, ); the flow field around bridge piers (Melville & Raudkivi, ); and the development of crescentic scour marks in a recent stream (Bhattacharya, ; Maity, Dasgupta, & Mazumder, ; Sarkar, et al, , ; Sengupta, , ) for prediction of palaeocurrent directions.…”

“…In turbulent boundary layers, coherent structures with large flux events have been proposed to explain the "bursting" phenomena responsible for two types of eddy motions name as "ejections" and "sweeps" (Cantwell, 1981;Robinson, 1991). These events are traditionally detected by conditional sampling through quadrant analysis in the (x, z)-plane (Willmarth & Lu, 1972) and their statistics have been investigated for a variety of flows and wall-roughness conditions, for example, experiments in open-channel (Hurther & Lemmin, 2000;Hurther, Lemmin, & Terray, 2007;Mazumder, 2007;Mazumder, Pal, Ghoshal, & Ojha, 2009;Nakagawa & Nezu, 1977;Nelson, Shreve, McLean, & Drake, 1995;Ojha & Mazumder, 2008;Venditti & Bauer, 2005); in wind-tunnel (Raupach, 1981); under an-ice boundary layer (Fer, McPhee, & Sirevaag, 2004); in atmospheric boundary layers (Hurther & Lemmin, 2003;Katul, Kuhn, Schieldge, & Hsieh, 1997;Katul, Poggi, Cava, & Finnigan, 2006;Sterk, Jacobs, & van Boxel, 1998), and in scour around vertical circular cylinders (Debnath, Manik, & Mazumder, 2012;Kirkil, Constantinscu, & Ettema, 2008;Sarkar, Chakraborty, & Mazumder, 2015;Sarkar, Chakraborty, & Mazumder, 2016). Besides the dominant role of the sweeps close to a rough wall, an "equilibrium region" is often observed in fully developed turbulent flows (Krogstad, Antonia, & Browne, 1992).…”