مهار ارتعاش ناشی از گرداب در سیلندر دایره ای توسط کنترل جریان بر پایه مکش

ABSTRACT Suppression of vortex-induced vibration of a circular cylinder using suction-based flow control

In recent years, long-span suspension bridges and cable-stayed bridges have been widely constructed worldwide due to their superior structural performance and elegant appearance. The key components of cable-stayed bridges, inclined cables, often vibrate under wind and rain, which are usually referred as vortex-induced vibration (VIV) (Main and Jones, 1999; Matsumoto et al., 2003; Zuo et al., 2008; Zuo and Jones, 2010) and rain-wind induced vibration (RWIV) (Hikami and Shiraishi, 1988), respectively. Although the VIV of the cables is self-limiting, it frequently occurs at low wind speeds. Frequent wind-induced vibration may induce fatigue damage to the cables. Therefore it is highly desirable to reduce the wind-induced vibrations for the optimized design and durability of the cable-stayed bridges. Besides using field measurements to monitor the VIV of full-scale cables on cable-stayed bridges (Zuo and Jones, 2010; Zuo et al., 2008), a number of laboratory studies have also been conducted in recent years with finite segment cable models (i.e., cylinder models) to investigate the VIV phenomena and explore effective strategies to suppress the VIV of bridge cables. For examples, Farivar (1981), Sakamoto and Arie (1983), Baban and So (1991) and Zdravkovich et al. (1989) carried out laboratory experiments to quantify the vibration responses and flow characteristics around cylindrical stay cable models of finite lengths.

Viscous damper devices have been widely used to control the VIV and RWIV of stay cables of cable-stayed bridges (Main and Jones, 2001; Persoon and Noorlander, 1999; Zhou and Xu, 2007). Main and Jones (2001) found an additional optimal damping ratio to the stay cable provided by the viscous damper. Wang and Xu (2007) employed an active stiffness control method to suppress the RWIVs of prototype stay cables. Li et al. (2007) and Liu et al. (2007) investigated the theory, algorithm and model test of the semi-active control of stay cables’ wind-induced vibrations using magnetorheological fluid dampers, which can effectively reduce the cable vibrations and increase the stay cables’ system damping ratios. Instead of controlling/suppressing the VIVs, an interesting idea has also been suggested recently to try to harvest wind energy from the VIVs. Bernitsas et al. (2008) designed a vortex induced vibration aquatic clean energy (VIVACE) converter. The VIVACE was based on the idea of maximizing (rather than spoiling) vortex shedding and exploiting (rather than suppressing) VIV. It introduced optimal damping for energy conversion while maintaining VIV over a broad range of vortex shedding synchronization.

While the control mechanisms of each type of damper device described above provided additional damping to the stay cables and increased their ability to resist wind-induced vibrations, those methods did not change or reduce the wind loads on the stay cables. Aerodynamic methods, including passive and active control approaches, can be used to reduce the wind loads on the stay cables. These methods can also increase the natural damping ratio of the stay cables. Matsumoto et al. (1992) and Flamand (1995) proposed the use of protuberances to suppress the RWIVs of stay cables. Gu and Du (2005) conducted wind tunnel tests using double-spiral wires to mitigate vibration. Owen and Bearman (2001) attached hemispherical bumps to the circular cylinder surface to control the vortex-induced vibration amplitudes of the cable models. Bao and Tao (2013) employed dual parallel plates which were symmetrically attached at the rear surface to control the wake flow of a circular cylinder. Oruç (2012) carried out a passive control for the flow structures around a circular cylinder by using a streamline screen which surrounded the circular cylinder. Wu et al. (2012) performed an experimental study on the suppression the VIV of a long flexible riser by using multiple control rods.

Many active flow approaches were also used to control the flow separation and flow-induced vibration. Wu et al. (2007) developed a moving-wall control strategy, e.g., appropriate traveling transverse wave, to manage the unsteady separated flow over a circular cylinder. This method allows the global flow to remain attached when there is a strong adverse pressure gradient and eliminates vortex shedding. Modi (1997), Munshi et al. (1997), Patnaik and Wei (2002) and Korkischko and Meneghini (2012) used momentum injections to control the flow field around the airfoils, flat plates, rectangular prisms, D-section prisms and circular cylinders; they found that the momentum injection method could effectively resist the wind-induced vortex and galloping instabilities. Grager et al. (2011) used a dynamic burst control plate to suppress the stall on an airfoil by preventing the low-Reynolds-number leading edge separation bubble from bursting. Tchieu and Leonard (2012) employed synthetic jet actuators to control the flow structures around an airfoil. Feng et al. (2010, 2011) and Feng and Wang (2010) conducted a series of experimental studies to investigate the effects of a synthetic jet on the unsteady vortex shedding in the wake of a circular cylinder. They reported that the synthetic jet positioned at the rear stagnation point of the cylinder would generate a vortex pair, which could have a significant influence on the vortex shedding modes in the wake of the circular cylinder.

Suction flow controls have been widely used to suppress the flow separation of airfoils (Qin et al., 1998; Greenblatt et al., 2006; Gbadebo et al., 2008; Chng et al., 2009), plates (Arcas and Redekopp, 2004Fransson and Alfredsson, 2003; Seal and Smith 1999) and circular cylinders (Delaunay and Kaiktsis, 2001; Fransson et al., 2004; Li et al., 2003; Patil and Ng, 2010). Delaunay and Kaiktsis (2001) studied the effects of base suction and blowing on the stability and dynamics of the flow around a circular cylinder at low Reynolds numbers (Reo 1⁄490). Slight blowing can stabilize the wake and reduce absolute instability in the near wake; a high enough suction can also stabilize the wake at Re447. Li et al. (2003) performed a complete control of vortex shedding with Reynolds numbers up to 110 via flow suction/blowing based on numerical simulations. It was observed that a short time window of flow control may suffice to suppress vortex shedding. Fransson et al. (2004) and Patil and Ng (2010) investigated suction flow control based on porosity of the entire or partial surface. The suction flow control has been found to lead to drag reduction, suppress the spanwise vortices formation, reduce the velocity fluctuation level and eliminate the oscillation of the lift.

In this paper, a steady suction flow control method is adopted to mitigate the VIV of a circular cylinder. The context of the present study is arranged as follows. In Section 2, a wind tunnel test for the VIV of a circular cylinder was set up in order to assess the effectiveness of using the suction control system for VIV suppression. In Sections 3–5, the measurement results in terms of the cylinder oscillations, pressure distributions and aerodynamic forces acting on the circular cylinder without suction flow control are analyzed and discussed. The measurement results with suction flow control are discussed in Section 6, followed by a section of conclusions derived from the present study.