# Steady-Suction-Based Flow Control of Flutter of Long-Span Bridge
###### Abstract  
The present wind tunnel study focuses on the effects of the steady-suction-based flow control method on the flutter performance of a 2 DOF bridge deck section model. The suction applied to the bridge model was released from slots located at the girder bottom. The suction rates of all slots along the span were equal and constant. A series of test cases with different combinations of suction slot positions, suction intervals, and suction rates were studied in detail for the bridge deck model. The experimental results showed that the steady-suction-based flow control method could improve the flutter characteristics of the bridge deck with a maximal increase in the critical flutter speed of up to 10.5%. In addition, the flutter derivatives (FDs) of the bridge deck with or without control were compared to investigate the fundamental mechanisms of the steady-suction-based control method. According to the results, installing a suction control device helps to strengthen aerodynamic damping, which is the primary cause for enhanced flutter performance of bridge decks. steady-suction-based control; bridge flutter; wind tunnel test; flutter control 20  
Furthermore, they optimized important TMD parameters for a better control effect. However, the excellent control performance of TMDs relies heavily on exact tuning to the controlled mode. Hence, the control causes severe deteriorations when the system parameters slightly deviate from their optimal values. To overcome the poor robustness of TMDs, [PERSON] and [PERSON] [3] first proposed multiple TMDs (MTMDs). These are composed of many small TMDs, which are each tuned to a different dominant frequency. Numerous studies have been carried out on MTMDs and have proved the robustness of the system [4; 5; 6]. Nevertheless, MTMDs occupy a large working space because of their complex configuration and are thus inapplicable to long-span bridges. Therefore, active mass dampers (AMDs) have been investigated and proposed. [PERSON] and [PERSON] [7] achieved a critical wind speed increase of up to approximately 16.5% through the implementation of an AMD to a bridge section model. Although the AMD control effect is remarkable, the economic efficiency is relatively unsatisfactory owing to the high external energy consumption. The flutter control measurements mentioned previously focus on optimizing the dynamic properties of a bridge structure. Modifying the flow field around the bridge deck and redistributing the aerodynamic forces exerted on the structure is another, more economical approach to mitigate wind-induced excitations. The so-called flow control method can be divided into passive and active methods. The passive approaches have been widely applied to practical engineering applications owing to their simplicity and reliability. The central stabilizer for the Runyang Bridge, the central slot for the Xihoumen Bridge, the Tsing Ma Bridge, the slot and stabilizer for the Akashi Kaikyo Bridge, and the guide vane for the Great Belt Bridge are a few examples [8]. However, passive control methods cannot solve the flutter problem for any velocity and attack angle of the oncoming wind. For this reason, active flow control methods that require external energy provided by auxiliary devices have been developed. Furthermore, the energy required for active flow facilities is much lower than that required for AMD systems because the former is only used to modify the flow field around the deck rather than to stabilize the structure directly. [PERSON] et al. [9] and [PERSON] et al. [10] experimentally investigated the effects of active flow control on the aerodynamic characteristics of a structure. The results showed that the boundary layer separation could be delayed, which led to a remarkable drag reduction and a significant improvement in the structural stability. In addition, in recent years, the study of fluid-conveying tubes has also received more and more attention from researchers [11; 12; 13].