# An Experimental Investigation of Passive Jet Control Method on Bridge Tower Wake
## 1 Introduction  
The cable system bridge is the most widely used large-span bridge system. With the increasing requirement of the span, a growing number of extra-large cable system bridges have come into service, and the wind resistance performance is the primary limitation to the span of the bridge. As the bridge span grows, the wind effect appears more complex, and unprecedented wind-induced phenomena could occur. The wake flow characteristics of bridge towers is an interesting research branch that could lead to the oscillation of the cable behind the tower. For cable-stayed bridges, some parts are under the influence of the tower wake, particularly the long stay cable. In susspender bridges, the suspenders near the tower are wholly in the influence region of the tower wake. The oscillation motion of these suspenders is much more complex due to the unstable wake flow. The characteristics of cylinder wake have been sufficiently investigated. [PERSON] [1] reviewed and further researched the Strouhal numbers of the wake of rectangular cylinders; [PERSON] [2] also investigated the wake frequencies by using a hot wire. [PERSON] and [PERSON] [3] used a two-layer k-\(\epsilon\) model to numerically study the aerodynamic characteristics of an infinite-length rectangular cylinder and gained a great agreement in the distribution of mean pressure, but the fluctuating pressure distribution was underestimated compared with the real model. [PERSON] et al. [4] investigated the wake-induced vibration (WIV) of tandem circular cylinders and considered the vibration as a consequence of the interaction between the wake and the structure, which differs from vortex-induced vibration (VIV). The experiment confirmed the wake displacement theory proposed by [PERSON] [5]. [PERSON] et al. [6] performed a numerical study on the phenomenon of WIV to a cylinder at a low Reynoldsnumber (_Re_). [PERSON] [7] reviewed the research of circular cylinder wakes, regarding wake-induced vibration as a form of VIV. The downstream cylinder is under the collective effect of vortex shedding from both upstream structures and itself. [PERSON] et al. [8] performed a two-dimensional numerical simulation of two tandem cylinders at low _Re_ flow and found that the WIV phenomenon comes to aggravation when the size of the cylinder upstream is larger than that downstream. [PERSON] et al. [9] conducted a wind tunnel test and a computational fluid dynamics (CFD) simulation to investigate the WIV of the suspenders in wake of a bridge tower. The experiment found that the suspender in the wake of the tower would carry out an elliptical orbit motion at a specific wind speed when the frequency of the wake fits the natural frequency of the suspenders. In another part, a tower with four corners cut decreases the RMS aerodynamic coefficient and facilitates the suppression of the WIV of suspenders. On the other hand, many studies have been conducted to investigate the suppression of VIV of cylinders. A technology based on suction and jet flow was confirmed to be effective. [PERSON] et al. [10; 11] modified the aerodynamic characteristics of cylinders by using fluidic actuators. The closed recirculating flow regimes generated by jet flow could be equivalent to a virtual surface which can modify the characteristics of aerodynamics. [PERSON] et al. [12] used synthetic jets to delay the separation point on cylinders, with the jet placed near the separation line. Many relevant studies were performed in the 21 st century [13; 14; 15] that also indicated that the turbulence of wake also can be decreased, and even the vortex street could be eliminated. [PERSON] et al. [16; 17] investigated the mode of wake by proper orthogonal decomposition, as the synthetic jet is applied to control the vortex shedding.