Experimental Study of the Effect of Displacement of Vanes Submerged at Channel Width on Distribution of Velocity and Shear Stress in a 180 Degree Bend

Abstract

Shear stress is a parameter of high significance. Through knowledge of this parameter, assessment of scour or sedimentations at different points of bed is made viable. Therefore, this paper investigated alterations in shear stress along the bend, specifically around a bridge pier, under the influence of applying submerged vanes at the upstream side of the bridge pier. With the aim of modeling submerged vanes, vanes of Plexiglas with a thickness of 20% of the pier diameter, a length of 1.5 times the pier diameter, and submergence ratio of 75% were utilized. The vanes were installed at a distance equal to 5 times the pier diameter from the pier center at a distance of 40 to 60% of the channel width from the inner bank at the upstream side of the bridge pier. Acoustic-Doppler Velocity velocimeter device was utilized for measuring three-dimensional velocity components. The experiments were conducted in a 1-meter-wide flume with a degree of curvature of 180. The results of the study suggested that upon reaching the bend apex, the maximum flow turbulence rate occurred in a transverse direction in the case of installing submerged vanes at a distance of 40% of the channel width from the inner bank towards the inner wall; while in the case of installing submerged vanes at a distance of 60% of the channel width from the inner bank, it occurred towards the outer wall, and it could be observed that the maximum longitudinal and vertical components of turbulence rate increased by 16 and 5.5% respectively upon increase in the distance of submerged vanes from the inner bank. Furthermore, the values of uw    and uv    turbulence shear stresses at the outer bank in the case of installing the vanes at a distance of 40% of the channel width from the inner bank were smaller than those in the case of installing the submerged vanes at a distance of 60% of the channel width from the inner bank.

Experimental investigation of local scour under two oblong piers of a bridge crossing a sharp bend river

“…The duration for all experiments was 6 h adopted based on the recommendations of previous studies with similar flow conditions through which the scour approached to the equilibrium state (Heidarnejad, Bajestan and Masjedi, 2010;Masjedi, Zeraat and Hydarnejad, 2011;Wang et al, 2016;Rasaei, Nazari and Eslamian, 2020). The depths of the bed at end of each run were determined using a point gauge and a laser instrument which were used by many researchers (Vaghefi et al, 2017;Chooplou and Vaghefi, 2019;Rasaei, Nazari and Eslamian, 2020;Moghaddassi et al, 2021;Sedighi, Vaghefi and Ahmadi, 2021). It was verified that the depth of the bed surface on a randomly set of points could be measured using a laser instrument and a point gauge, with a correlation coefficient of 0.98, as shown in Table S1.…”

“…For a pair of V-shaped piers, the scouring was greater on the pier closer to the bends beyond the border. Chooplou and Vaghefi (2019) studied variations in shear stress along a bend, particularly around a bridge pier, when submerged vanes were implemented upstream of the bridge pier. As the flow enters the bend, the secondary flow strength has two maximum values: one at the bend apex and another at the bend end.…”

Effect of Bridge Piers Locations and Flow Intensity on Morphological Change in a 180-Degree River Bend

“…A manually controlled valve selected the desired discharge. The depths of the bed at the end of each run were determined using a point gauge and a laser instrument which have been used by many researchers as [13,14,16,21,23,24] .…”

“…The most incredible scour depth was 3.3 times the pier diameter at an intensity of 8.5 and followed a logarithmic curve. Although local scour at a bend is extremely important, and numerous studies have been undertaken to date, most of the research within the curve was based on the incipient motion at threshold intensity, some of which were as follows: [11][12][13][14][15][16][17][18].…”

Experimental Investigation on the Effect of Increasing the Collar Thickness on the Flow Pattern around the Oblong Pier in 180˚ Sharp Bend with Balanced Bed

“…Therefore, understanding the flow pattern around the pier and on the condition of locating the pier on the bend is highly important. In the meantime, the existence of collar adjoining structure used for reducing scour around the pier increases this complexity (Abdi Chooplou and Vaghefi, 2019). Many researchers from the past so far have been trying to study the structure of the flow around the bridge piers with numerical and experimental methods.…”