Alluvial channel hydrodynamics around tandem piers with downward seepage
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RESEARCH ARTICLE
Alluvial channel hydrodynamics around tandem piers with downward seepage Rutuja CHAVANa, Wenxin HUAIb, Bimlesh KUMARc* a
Department of Civil Engineering, Maulana Azad National Institute of Technology Bhopal, Bhopal, Madhya Pradesh 462003, India Department of Harbor, School of Water Resources and Hydropower Engineering, Wuhan University, Wuhan 430072, China c Department of Civil Engineering, Indian Institute of Technology Guwahati, Guwahati 781039, India b
*
Corresponding author. E-mail: [email protected]
© Higher Education Press 2020
ABSTRACT In this paper, we report the turbulent flow structures and the scour geometry around two piers with different diameters. An experiment was conducted on a non-uniform sand bed with two types of tandem arrangements, namely, pier (T1) with a 75 mm front and 90 mm rear, and pier (T2) with a 90 mm front and 75 mm rear, with and withoutseepage flows, respectively. A strong wake region was observed behind the piers, but the vortex strength diminished with downward seepage. Streamwise velocity was found to be maximum near the bed downstream of the piers and at the edge of the scour hole upstream of the piers. Quadrant analysis was used to recognize the susceptible region for sediment entrainment and deposition. Upstream of the piers near the bed, the moments, turbulent kinetic energy (TKE), and TKE fluxes were found to decrease with downward seepage, in contrast to those in a plane mobile bed without piers. The reduction percentages of scour depth at the rear pier compared with the front one were approximately 40% for T1 and 60% for T2. Downward seepage also resulted in restrained growth of scouring with time. KEYWORDS
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scour, seepage, Strouhal number, tandem arrangement, turbulent characteristics
Introduction
In alluvial channels, complicated flow structures around bridge piers result in scouring, which causes structural collapse. Many researchers have discovered that the vortex systems developed around bridge piers are responsible for the scouring around piers [1–6]. Melville [1] and Chiew [4] stated that a vortex system that consists of a horseshoe vortex and wake vortices is the primary cause of scouring around piers. The horseshoe vortex increases the velocity near the bed, and the wake vortices maintain the sediment particle in suspension. Qadar [3] reported that flow separates at a pier and rolls up near the bed region, thereby causing scouring around the piers. According to Melville and Coleman [7], a flow field can be characterized by a downflow at the upstream face of the pier, horseshoe vortex near the bed, and surface roller and wake vortices behind the pier. Izadinia et al. [8] investigated the flow characteristics around a single pier under a fixed bed Article history: Received Nov 25, 2018; Accepted Sep 28, 2019
condition. Previously published research has shown that the turbulent flow characteristics around a single bridge pier are complex. Thus, these characteristics can become increasingly complex around a group of piers. Currently, groups of piers ar
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