Vortex dynamics and turbulence transport in flow around a near-wall rectangular cylinder

This study investigates the vortex dynamics and turbulent characteristics of flow around a near-wall rectangular cylinder for varying gap ratios (G/D=0.1, 0.3, and 0.9) and aspect ratios (L/D=5, 10, and 15). Kelvin–Helmholtz vortices form from the upper leading edge (ULE) shear layer, with secondary instabilities leading to three-dimensional vortex structures. For small gap ratios (G/D=0.1 and 0.3), strong near-wall effects suppress the formation of lower leading edge (LLE) shear layers, whereas at G/D=0.9, both LLE and lower trailing edge shear layers form, increasing vortex complexity. The downstream wall recirculation also decreases with increasing G/D. For smaller aspect ratios (L/D=5), the ULE recirculation spans the upper side of the cylinder, while for larger L/D values (L/D=10, 15), hairpin vortices form on the upper side. The growth of the ULE shear layer, quantified by vorticity thickness (δω), is influenced by the near-wall effect and exhibits three growth regions. Turbulent fluctuations, reflected in total turbulent kinetic energy (TKE) and Reynolds stresses, are influenced by both G/D and L/D. Fluctuations decrease as G/D increases from 0.1 to 0.3 due to weakened vortex–wall interactions, while alternating vortex shedding at G/D=0.9 intensifies fluctuations. The integration of TKE and Reynolds stresses reveals single and double peaks for L/D=5 and L/D=10,15, respectively. TKE production analysis shows that P11 dominates the total TKE for smaller gap ratios, while P22 for wall-normal TKE becomes more significant at G/D=0.9. These findings provide insight into the complex vortex dynamics and turbulence mechanisms in near-wall bluff body flows.