Impacts of the bottom vortex on the surrounding flow characteristics of a semi-submerged rectangular cylinder under four aspect ratios

Abstract Vortex has attracted attention because it is the main factor affecting the flow characteristics around offshore structures. This paper researches the flow field variations around a semi-submerged rectangular cylinder (SRC) under four aspect ratios, thereby revealing the bottom vortex effects on the flow field at Reynolds number = 36300. According to the particle image velocimetry (PIV) data, the RNG k-ε model is selected as an applicable turbulence model for studying SRC flow characteristics. From the results, the bottom vortex generation and streamwise velocity are inseparable. As the draft increases, the increased range of the bottom vortex would directly interfere with the flow characteristic around the SRC. Since the wake vortex forms a reattachment state when the SRC pierces the free surface, its flow field could be disturbed by the bottom vortex. Furthermore, the bottom vortex also affects the extreme point position of the boundary layer characteristic at the SRC bottom.