The flow and turbulence structure at a rectangular bridge pier with a low angle of attack (original) (raw)
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Acta Geophysica, 2012
Recent investigations on the dynamics of the turbulent horseshoe vortex system (THV) around cylindrical piers have shown that the rich coherent dynamics of the vortical structures is dominated by low-frequency bimodal fluctuations of the velocity field. In spite of these advances, many questions remain regarding the changes of the flow and sediment transport dynamics as scour progresses. In this investigation we carry out laboratory experiments to register the development of the scour hole around a cylindrical pier in a fine-sand bed (d 50 = 0.36 mm). We use the bathymetry measured in the experiment to simulate the flow field employing the detached-eddy simulation approach (DES), which has shown to resolve most of the turbulent stresses around surface-mounted obstacles. From these simulations we compare the dynamics of the THV to the flat-bed case, and analyze the effects on particle transport and sediment flux using the Lagrangian particle model of Escauriaza and Sotiropoulos (2011...
Study of flow turbulence around a circular bridge pier in sand mined stream channel
Proceedings of the Institution of Civil Engineers - Water Management, 2019
Experiments were performed in a sand bed channel to investigate the effects of a mining pit on the hydrodynamics around circular bridge piers. Mean velocity profiles, Reynolds stresses, kinetic energy fluxes and scales of turbulence were analysed at critical locations along the channel bed as well as in the proximity of the pier. At the approach location where flow had passed over the pit and was approaching the pier, substantial increments in the near-bed velocities, bed shear stress and Reynolds stresses were observed. Dredging of the pit increased the strength of the horseshoe vortex in the scour hole region and also amplified the shedding frequency of trailing vortices at the rear of the pier. These effects may be instrumental in the alteration of local scour as well as erosion and deposition patterns around bridge piers.
The objective of the present paper is to investigate experimentally the flow field and the local scour around bridge pier of different shapes on a sediment bed. Experiments were carried out using individual piers of rectangular, oblong, trapezoidal, triangular and lenticular shapes with a common aspect ratio to compare the flow field and scour geometry among the shapes at identical flow conditions. The novelty of this study is to identify the scour structures due to different pier shapes and associated mean flows and turbulence, which are responsible for generation of scour. A 3D Micro-acoustic Doppler velocimeter (ADV) was used to record the instantaneous velocity data for five different discharges. It is observed that upstream scour depth was maximum at the leading edge of the rectangular pier, and minimum at the same location for the lenticular. Here, the horseshoe vortex is the main agent of the scour development for any kind of pier shapes, even for the sharp edges, though there is an immediate bifurcation of flow in the triangular and lenticular-nosed piers, where the scour formation is less than the others. The changes in mean velocities and Reynolds stresses due to the pier shapes are discussed and compared to that of flat-bed surface. Since the shape of the pier alters the flow and turbulence, one can expect large variations in flow behavior, and hence different scour formations are observed. The results can be used to identify scour structures around the piers of different shapes for designing and suggesting appropriate protection measures.
4th International Congress of Engineering and Natural Sciences (ICENSS 2024),May 24-25 , 2024
Local scour is a significant factor contributing to the bridge's collapse, which is defined by the erosive action of sediment-water flow in river systems. Thus, studying scouring is a crucial approach to assess the potential for bridge failure caused by scour. This study investigates the local scour phenomenon in non-cohesive bed conditions using both experimental in a laboratory flume and numerical approaches by applying the computational fluid dynamics (CFD) method with FLOW 3D software to model and compute local scour in the same type of bed. Experimental modeling in live bed flow conditions reveals that water depth is the primary factor influencing local scour depth, with high-velocity water exceeding critical velocity resulting in increased scour depth aligned with pier depth. Sediment accumulation occurs downstream from the scour hole, with scour development reaching equilibrium quickly. The developed numerical model, FLOW 3D, proves efficient in simulating scour depth and flow around bridge piers, with mesh quality significantly impacting modeling accuracy.