Numerical study on self-excited forces and flow fields for a thin plate under a sinusoidal non-stationary wind condition

Long hangers around the bridge tower are subjected to severe vibrations caused by the tower wakes. This study adopted an active suction/blowing control measure at the tower corners to control hanger vibrations and included four combination measures: upstream suction (US), upstream blowing (UB), downstream suction (DS), and downstream blowing (DB). The effects of control cases on the near-wake flow structures of the tower were first studied in two-dimensional RANS simulation, and the vibration behaviors of the hanger and control mechanism were further analyzed. The cases associated with UB and DS cannot effectively suppress hanger vibrations, and both lead to unfavorable upward trends in the aerodynamic coefficients of the tower. Especially for the cases associated with DS, at a specific control speed, the second-order frequency of the drag coefficient of the hanger is very close to its natural frequency, resulting in significant longitudinal vibration. The cases associated with US and DB are effective control schemes with longitudinal peak amplitudes of the hanger reduced by 94.1% and 94.5%, and lateral peak amplitudes reduced by 95.8% and 97.0%, respectively, compared with the case baseline. This is because the dominant frequency of the lift of the hanger is away from its natural frequency, and the fluctuating wind loads on the hanger are effectively suppressed. Finally, the control effect and vibration suppression mechanism for typical cases were further reproduced in three-dimensional large eddy simulations.

Numerical simulations on flow control of the long hanger around a bridge tower based on active suction and blowing method

Hu,

Wang,

Han

et al. 2023

Numerical study of wind loads on the streamlined bridge deck in the translating tornado-like vortex

Zhang,

Wang,

2023

Wind load is one of the key factors affecting the structural safety of long-span bridges. However, the tornado-induced load on the streamlined bridge deck is rarely studied and the influence of the translation of tornado vortices has not been considered. This study develops a computational fluid dynamics (CFD) method to simulate the translating tornado-like vortex (TLV) to investigate the tornado-induced load on the streamlined bridge deck. First, the numerical method for simulating a translating TLV is introduced and the model of the streamlined bridge deck of a kilometer-level bridge is constructed and verified. The characteristics of the flow field around the bridge deck are then analyzed. Finally, the lift force, drag force, and torsional force on the bridge deck in the translating TLV are investigated and compared with those in the straight-line wind field and the stationary TLV. The non-dimensional forces obtained in the translating TLV are provided as a reference for calculating the tornado-induced load on a streamlined bridge deck. The result shows that the wind load on the bridge deck in the TLV changes along the spanwise direction, which is significantly different from that in the straight-line wind field. In the translating TLV, the bridge deck sustains the lift force induced by the updraft and the drag force induced by the translating velocity. The load on the bridge deck in the translating TLV is significantly larger than that in the straight-line wind and the stationary TLV, which indicates that the translation effects of tornadoes should not be ignored.

Effect of wingtip bending morphing on gust-induced aerodynamics based on fluid-structure interaction method

Zheng,

Dai,

Yang

et al. 2023

This paper investigates the effect of wingtip bending morphing on gust-induced aerodynamics based on the fluid–structure interaction (FSI) method at Re = 40 000. First, an explicit spatiotemporal numerical model for a wingtip bending morphing on a wing with a semi-aspect ratio of 4 is deduced, considering geometrical nonlinearity under large morphing amplitude. A modal-based FSI framework is developed to consider the elastic deformation, active wingtip morphing, and gust. The shear-stress transport-γ model is introduced. The above FSI method is validated by gust response experimental results. The mitigation effects of active bending morphing on gust-induced aerodynamics at different phase offset, gust ratios (GR), and flare angles are investigated. Under GR = 0.2 and flare angle = 0, wingtip bending morphing achieves the best mitigation effect when the phase offset is π/2. As GR increases to 0.4, the optimum phase offset shifts to π/3 and the alleviation rate decreases. The mitigation rate increases with the flare angle. Under GR = 0.4 and flare angle = 30°, the optimum phase offset is π/6, in which case the lift response is reduced by 37%, and wing root bending moment response is reduced by 73% relative to the baseline case. The flow field and vortex evolution result infers that the wingtip bending morphing decreases the spanwise width of the leading-edge vortex and reduces the area of low-pressure zones on the suction side, thereby mitigating gust-induced aerodynamics. The results indicate that active wingtip bending morphing has great potential for gust load alleviation for future aircraft.