Review of the excitation mechanism and aerodynamic flow control of vortex-induced vibration of the main girder for long-span bridges: A vortex-dynamics approach

Twisted-wind effect on the flow field of tall building

The flow through tandem square cylinders was investigated at a Reynolds number of 100 for oscillation amplitudes A = 0.1 D to 0.7 D and gaps L = 2.0 D, 5.0 D, and 6.0 D, where D is the width of the cylinders. A moving reference frame method combined with the spectral/hp element method was employed to simulate the two-dimensional flow in the lock-in regime. Fluid forces, vorticity fields, power spectrum density, and pressure distribution were first investigated. Since surface pressure is directly connected with fluid forces, pressure and velocity field were synchronously analyzed by employing optimal dynamic mode decomposition. An underlying link between fluid forces and coherence modes was then uncovered. The results reveal that the move-induced forces and flow structures strongly depend on gaps and amplitudes in the lock-in regime. With respect to the dynamic mode decomposition analysis, odd-order modes contribute to lift forces, while even-order modes result in drag forces. The flow structures are dominated by at most three modes; as the amplitude increases, the high-order mode energy increases, coinciding with corresponding power spectrum density results of forces. Typical 2S, 2P, and C(2S) wakes were observed for various gaps and two representative amplitudes ( A/D = 0 and 0.7), and their dominant modes show distinctive differences that lead to different local pressure shapes on the cylinders. It is the combined effects of local mode shape and global mode energy that account for the change in fluid forces for various gaps and two oscillating amplitudes.

Dynamic mode decomposition analysis of the two-dimensional flow past two transversely in-phase oscillating cylinders in a tandem arrangement

It is now well-known that the wake transition regime for a circular cylinder involves two modes of small-scale three-dimensional instability, modes “A” and “B”, occurring in different Reynolds number ranges. These modes are quite distinct in spanwise lengthscale and in symmetry, and they are found to scale on different physical features of the flow. Mode A has a large spanwise wavelength of around 3–4 cylinder diameters, and scales on the larger physical structure in the flow, namely the core of the primary Karman vortices. The feedback from one vortex to the next gives an out-of-phase streamwise vortex pattern for this mode. In contrast, the mode B instability has a distinctly smaller spanwise wevelength (1 diameter) which scales on the smaller physical structure in the flow, namely the braid shear layer. The symmetry of mode B is determined by the reverse flow behind the bluff cylinder, leading to a system of streamwise vortices which are in phase between successive half cycles. The symmetries of both modes are the same as the ones found in the vortex system evolving from perturbed plane wakes studied by Meiburg and Lasheras (1988) and Lasheras and Meiburg (1990). Furthermore, the question of the physical origin of these three-dimensional instabilities is addressed. We present evidence that they are linked to general instability mechanisms found in two-dimensional linear flows. In particular, mode A seems to be a result of an elliptic instability of the near-wake vortex cores; predictions based on elliptic instability theory concerning the initial perturbation shape and the spanwise wevelength are in good agreement with experimental observations. For the mode B instability, it is suggested that it is a manifestation of a hyperbolic instability of the stagnation point flow found in the braid shear layer linking the primary vortices.

Three-dimensional instabilities in wake transition

Vortex-induced vibration control of a flexible circular cylinder using a nonlinear energy sink

Flow past a transversely oscillating cylinder at lock-on region and three-dimensional Floquet stability analysis of its wake

Experimental study on suppressing vortex-induced vibration of a long-span bridge by installing the wavy railings

External suction-blowing method for controlling vortex-induced vibration of a bridge

Vortex-induced vibration control of a streamline box girder using the wake perturbation of horizontal axis micro-wind turbines

The addition of railings inevitably changes the aerodynamic shape of a main girder, which in turn has a great effect on the vortex-induced vibration (VIV) of a long-span bridge. To ensure ...

Jian Zhan

Papers

Flow past a transversely oscillating cylinder at lock-on region and three-dimensional Floquet stability analysis of its wake

Experimental study on suppressing vortex-induced vibration of a long-span bridge by installing the wavy railings

External suction-blowing method for controlling vortex-induced vibration of a bridge

Vortex-induced vibration control of a streamline box girder using the wake perturbation of horizontal axis micro-wind turbines

Control of Vortex-Induced Vibration of a Long-Span Bridge by Inclined Railings