Abstract
A turbulent horseshoe vortex (HV) system around a wall-mounted cylinder in open channel is characterized by random variations in vortex features and an abundance of vortex interactions. The turbulent HV system is responsible for initiating the local scour process in front of the cylinder. The evolution of the turbulent HV system is investigated statistically and quantitatively with time-resolved particle image velocimetry. The cylinder Reynolds numbers of the flow are 8600, 10,200, and 13,600, respectively. A novel vortex tracking method was proposed to obtain the variations in position, size, and strength of the primary HV (PHV) which dominates the system most of the time. Relationships between the various features of the PHV during its evolutionary process were obtained through correlation analyses. Results show that the dimensionless mean lifespan of the PHV is about 5.0. Statistically, the downstream movement of the PHV toward the cylinder is accompanied with its bed-approaching movement and decreasing in size, and the opposite is true. The circulation strength of the PHV decreases and increases dramatically in the region downstream of its time-averaged position when the PHV approaches and departs from the cylinder, respectively. Meanwhile, mechanisms responsible for the generation, movement, variation, and disappearance of the PHV are re-investigated and enriched based on its interactions with vortices in the separation region and structures in the incoming flow. The obtained change trends of the features of the PHV and the underlying mechanisms for its evolution are valuable for predicting and controlling the initial stage of the local scour in front of cylinders.
Highlights
Flows around a wall-mounted circular cylinder appear in a large number of technical and environmental applications, such as river flows past bridge piers and pile foundations [1,2,3]
The evolution of the turbulent horseshoe vortex (HV) system around a circular cylinder mounted on the flat bed of an open channel was investigated quantitatively and statistically with time-resolve PIV measurements
Among vortices comprising the turbulent HV system, the primary HV (PHV) was selected as the representative vortex, and was tracked continuously in successive velocity fields with a novel method to obtain the time histories of its position, size, coherence, and circulation strength
Summary
Flows around a wall-mounted circular cylinder appear in a large number of technical and environmental applications, such as river flows past bridge piers and pile foundations [1,2,3]. Agui and Andreopoulos [15] visualized the flow structures around a circular cylinder for cylinder Reynolds numbers, ReD , of 1.0 × 105 and 2.2 × 105 They observed that the flow field upstream of the cylinder is always dominated by a much more stable and larger primary HV (PHV). For the flow at ReD = 39,000, the system was found to be dominated by two primary horseshoe vortices (PHVs) These two HVs move upstream and downstream, respectively. Kirkil and Constantinescu [17] adopted the LES and DES approaches to study flows around a circular cylinder with ReD = 16,000 and 500,000, respectively The underlying mechanisms responsible for the generation, disappearance, large-scale streamwise movements, and strength variations of the PHV were re-investigated
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
