Influence of boundary layer thickness and gap ratios on three-dimensional flow characteristics around a circular cylinder in proximity to a bottom plane

OCEAN ENGINEERING

卷:226

Article

Zhang, Zhimeng¹  Ji, Chunning^1,2  Chen, Weilin¹  Hua, Yang¹  Srinil, Narakorn³ 

[1] Tianjin Univ, State Key Lab Hydraul Engn Simulat & Safety, Tianjin 300350, Peoples R China

[2] Tianjin Univ, Key Lab Earthquake Engn Simulat & Seism Resilienc, Tianjin 300350, Peoples R China

[3] Newcastle Univ, Sch Engn, Newcastle Upon Tyne NE1 7RU, Tyne & Wear, England

关键词: Direct numerical simulation;    Circular cylinder;    Gap ratio;    Flow three-dimensionality;    Wake transition;    Vortex shedding pattern;   

DOI  :  10.1016/j.oceaneng.2021.108858

来源: Elsevier

【 摘 要 】

Three-dimensional flow characteristics around a horizontal circular cylinder near a plane boundary are investigated using a Direct Numerical Simulation (DNS) at the Reynolds number of 350. The cylinder has a gap-todiameter ratio G/D = 0.2, 0.6 and 1.0, with a boundary layer thickness-to-diameter ratio delta/D = 0, 0.7 and 1.6. The hydrodynamic forces, pressure distributions, vortex shedding patterns, wake transitions and flow threedimensionality features are presented and discussed. The hydrodynamic forces and pressure distributions are strongly dependent on G/D and delta/D. The mean drag coefficient decreases with increasing delta/D, whereas the mean lift coefficient increases with decreasing G/D. The pressure coefficient distribution around the cylinder changes from being asymmetric to symmetric as G/D is increased from 0.2 to 1.0, resulting in a development from the suppressed state to the fully developed state of the vortex shedding. As for the vortex dynamics, the strength and size of primary vortices decrease with increasing delta/D. The crossing trajectories exhibiting an inversion on the position of clockwise and counterclockwise vortices can only be observed in the wake when G/D is greater than a critical value below which the vortex shedding is completely suppressed, and when the cylinder is partially immersed into the boundary layer (G/D < delta/D < G/D + 1). An intrinsic switching between the single- and dualfrequency modes of the drag coefficient is found to be related to a complex interaction between the boundary layer and the near-wake vortex shedding. For a specific G/D, the flow three-dimensionality represented by the spanwise kinetic energy is found to decrease with increasing delta/D. For a specific delta/D, the spanwise kinetic energy shows a non-monotonic trend with the variation of G/D.

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