Turbulent Flow Field around Horizontal Cylinders with Scour Hole

Abstract

This study presents the results of an experimental investigation on the flow-structure interactions at scoured horizontal cylinders, varying the gap between the cylinder and the bed surface. A 2D Particle Image Velocimetry (PIV) system was used to measure the flow field in a vertical plane at the end of the scouring process. Instantaneous and ensemble-averaged velocity and vorticity fields, viscous and Reynolds stresses, and ensemble-averaged turbulence indicators were calculated. Longitudinal bed profiles were measured at the equilibrium. The results revealed that suspended and laid on cylinders behave differently from half-buried cylinders if subjected to the same hydraulic conditions. In the latter case, vortex shedding downstream of the cylinder is suppressed by the presence of the bed surface that causes an asymmetry in the development of the vortices. This implies that strong turbulent mixing processes occur downstream of the uncovered cylinders, whereas in the case of half-buried cylinders they are confined within the scour hole.

Bed Roughness Effects on the Turbulence Characteristics of Flows through Emergent Rigid Vegetation

“…Vegetation on river banks and floodplains plays an extremely important role in mitigating the adverse anthropogenic effects on the environment [1][2][3][4][5], especially in the areas most affected by human alterations (presence of bridge piers and abutments, pipelines, etc.) [6][7][8]. However, vegetation can have a significant impact on the flow hydrodynamics, influencing the exchange of mass and momentum across the river section [4,[9][10][11], as well as on fluvial geomorphology, water quality, and biodiversity (e.g., [12,13]).…”

Turbulent Flow through Random Vegetation on a Rough Bed

“…Water 2021, 13, x FOR PEER REVIEW 4 of 14 etation, bed roughness or man-made structures acting as an obstruction for the flow generate turbulence and affect the entire flow velocity distribution, modifying the turbulence behavior [30,31]. In Table 1, the hydraulic conditions of the experimental study are reported.…”

“…Nevertheless, they could represent a new dataset that, for instance, may be used for the calibration of advanced numerical models. In fact, as is known, vegetation, bed roughness or man-made structures acting as an obstruction for the flow generate turbulence and affect the entire flow velocity distribution, modifying the turbulence behavior [30,31].…”

Anisotropy in the Free Stream Region of Turbulent Flows through Emergent Rigid Vegetation on Rough Beds

“…Positive values of the vorticity indicate clockwise fluid motion; on the contrary, negative values refer to counterclockwise direction. Specifically, the rotational direction provides information about flow acceleration and deceleration in the near-bed flow: counterclockwise rotation induces flow acceleration, with a downward transport of momentum in the downstream direction; clockwise rotation causes flow deceleration, with upward transport of momentum in the upstream direction [25,26]. It is evident that the vorticity changes its signs alternatively in the flow layer affected by the presence of both vegetation and bed roughness.…”