Flow patterns and vortex related characteristics of tandem rectangular structures with recessed corners

Focused on optimizing the vortex-induced vibration (VIV) of bridge towers, this study explores the aerodynamic characteristics of tandem rectangular cylinders with varying corner recess sizes through three-dimensional large eddy simulation. The effects of corner recess on aerodynamic forces, mean and fluctuating pressure distributions, flow structures, separation bubbles, and Strouhal numbers are thoroughly analyzed using five numerical simulations. The results reveal that the key factor driving VIV in tandem cylinders is the significant fluctuating lift experienced by the downstream cylinder. Corner recesses lead to smaller separation shear layer scales and earlier flow reattachment, thus reducing the vortex structure scale around the downstream cylinder. However, further increasing the recess size may cause stronger gap and wake vortex intensities, with increased velocity gradients counteracting the positive feedback from the reduction in the vortex scale. Therefore, the study suggests that a moderate corner (the recessed corner ratio is 12% of the cylinder's length and width) provides an optimal flow field around the two cylinders, balancing the dynamic relationship between the enhancement of the velocity gradient and the suppression of vortex structures. This results in a fluctuating lift force characterized by a slight increase at the upstream cylinder and a significant decrease at the downstream cylinder, ultimately minimizing the VIV amplitudes of the tandem cylinders. These findings underscore the importance of corner recess size in achieving aerodynamic stability, offering practical insights for modifying large bridge towers to mitigate wind-induced oscillations.