## 3 Aeroelasticity and Aerodynamics of Cable-Supported Bridges
### Vortex-Induced Vibration
#### 3.2.3 CFD Studies of Vortex-Induced Vibrations
Secondly, through a Reynolds number sensitivity study, it was found that for low-Reynolds number conditions (which were commonly adopted in wind tunnel tests) small variations in the Reynolds number significantly altered the aerodynamic forces. Due to the limitations of experimental apparatus, it can often be challenging to precisely control the Reynolds number. Therefore, it was suggested that the wind tunnel tests used in the comparison underestimated the VIV amplitude. Aerodynamic countermeasures of VIVs  
[PERSON] and [PERSON] (2018) performed 3D LESs to study the effect of two aerodynamic countermeasures--fairings and double flaps--on the suppression of VIVs. Compared to the wind tunnel results, the LESs closely matched estimates of the VIV amplitude and corresponding wind velocities. The double flaps had a marginal effect on reducing the VIV amplitude, whereas the fairings stimulated a slightly larger vibration. Critical wind velocities of VIVs were also identified through forced oscillation simulations, in which the motion of the deck was prescribed, saving computational effort compared with the free oscillation method. However, both the simulations and wind tunnel tests were conducted in smooth-flow conditions in which the effect of incident turbulence was neglected. While this saved on computational effort, it limited the applicability of the findings. [PERSON], [PERSON] and [PERSON] [75] conducted both wind tunnel tests and 2D LESs to study the performance of guide vanes and spoilers on the mitigation of VIVs. Both wind tunnel tests and CFD simulations were based on a 1:20 scaled bridge section model. They found that installing spoilers on crash barriers can almost eliminate the vibration due to vortex shedding. However, the performance of guide vanes depends on where they are installed--the guide vane will not work when it is placed on the inclined web plate. A limitation of this work is that simulations and wind tunnel tests were only performed at an angle of attack of 3\({}^{\circ}\). Furthermore, the effect of incidence turbulence was neglected. Further studies that consider various angles of attack and incidence turbulence conditions would expand the applicability of the findings. To test the performance of the vortex generator in suppressing VIVs, [PERSON], [PERSON] and [PERSON] [83] conducted DDESs with the k-\(\omega\) SST turbulence model on a streamlined box girder. By comparing to experimental results and field measurement data, the DDESs performed well in predicting the flow field around the bridge deck. The spanwise eddies were significantly mitigated and the vortex-induced aerodynamic forces were greatly reduced, especially on the wake-side, which showed that the vortex generator was able to control the vortex shedding that induced the VIV. However, there are two significant limitations to this study. Firstly, the simulations were performed in smooth-flow conditions where only a 0.1% turbulence intensity was used. Secondly, the simulations were performed with a null angle of attack. To fully demonstrate the performance of the vortex generator, a wide range of flow conditions and geometric configurations should be incorporated into the simulations. [PERSON] et al. [84] performed 2D URANS simulations with the k-\(\omega\) SST turbulence model on a streamlined box girder. Two types of nonstructural elements were added to the bridge deck geometry, the guardrails and the maintenance tracks. The effect of these secondary elements on the VIV performance of the girder was investigated. It was found that increasing the height of windward guardrails can significantly reduce the VIV but will also increase the global drag forces acting on the girder. In contrast, optimizing the position of the maintenance track, i.e., moving the maintenance track closer to the centreline of the deck, only enhanced the VIV performance of the girder slightly. These findings present interesting insights on the VIV suppression of streamlined box girder.