Yewei Huang

This study investigates the passive control of vortex-induced vibration (VIV) on a rectangular column with a side ratio of 1.25 using triangular vortex generators (VGs) through wind tunnel tests. The optimal geometric parameters of VGs were determined via aerodynamic force measurements. Flow visualization, particle image velocimetry (PIV), and proper orthogonal decomposition (POD) analysis were employed to reveal the control mechanism and the wake field modification. Results show that at zero yaw angle, VGs effectively suppress VIV by generating inter-wing vortices that energize the boundary layer and delay flow separation, reducing the root mean square (RMS) lift coefficient by over 50%. The wake turbulence kinetic energy and swirling strength are significantly attenuated, and the regularity of vortex shedding is weakened. However, the control effectiveness is highly dependent on the yaw angle: it is optimal at 0°, deteriorates at 10° due to adverse shear layer excitation, and becomes negligible beyond 20°. Notably, at small yaw angles where tower-wake-induced vibration (TWIV) of suspenders typically occurs, VGs still effectively reduce the large-scale vortex intensity in the near-wake region, suggesting their potential for indirectly mitigating TWIV by suppressing the vortex shedding from the tower. These findings provide practical guidelines for applying VGs in wind-sensitive civil engineering structures.

This paper investigates the effects of two control measures on vortex-induced vibration and wake-induced vibration of suspension bridge cables through wind tunnel experiments. For a single cable, a passive suction/jet ring arrangement is proposed, and its vortex-induced vibration suppression performance under different density configurations (single-segment and two-segment dense arrangements) is analyzed. Experiments show that the total length of the ring is positively correlated with the control effect. The two-segment arrangement is significantly better than the single-segment arrangement when the total length is 1/4 of the cable length, with a maximum reduction in vibration displacement of 88%. For double cables, a spacer with an integrated tuned mass damper (TMD) is used. The results show that the TMD can effectively suppress vortex-induced vibration and wake-induced vibration. Its control effect depends on the installation position and the damper’s natural frequency. Installation at mid-span and 1/4-span positions can significantly reduce the vibration response, especially for suppressing first-order mode vibration. This study provides an optimized aerodynamic and damper combination scheme for cable wind vibration control.

Airfoil flow separation induces reverse flow in the shear layer. Focusing on this phenomenon, surface modification is adopted on flexible upper-surface flaps (USFs) to enhance their performance in flow separation control. Specifically, the surface modification refers to designing inclined protrusions on the tip of flexible USFs, which face the reverse flow. Systematic wind tunnel experiments, You Only Look Once v8 object detection, aerodynamic force measurements, and flow field visualization were employed to investigate the protrusions' effects on USFs' flapping dynamics, aerodynamic performance, and flow control mechanisms. The experimental results demonstrated that inclined protrusions decrease the critical Reynolds number for flexible USFs to enter the unsteady flapping state and slow the evolution of their flapping dynamics with increasing Reynolds number. These changes expand the Reynolds number range where flexible USFs achieve airfoil flow separation control, resulting in a maximum lift improvement of 10.4%, a drag reduction of 7.4%, and a 21.6% increase in the lift-to-drag ratio. Interestingly, millimeter-scale inclined protrusions are sufficient to induce flapping of flexible USFs, indicating that flexible USFs are highly sensitive to surface boundary conditions. It was also found that increasing protrusion height alters the airfoil's aerodynamic shape, enhancing lift even when the modified USFs are attached to the airfoil.