We present results from large-scale towing-tank tests conducted to explore the use of jets to suppress the vortex shedding from a circular cylinder immersed in a uniform turbulent stream. The jets were produced by injecting water through a number of discrete holes arranged along the cylinder's stagnation line. Several combinations of holes numbers, sizes and center-to-center distances were tested. Also, the effects of varying the ratio of flow rate from each hole to the flow rate of the incident current were examined. In all cases, it was found that strength of vortex shedding can be drastically reduced by the jets provided that the jet to incident flow rate ratio exceeds a critical value.
Ever since the undesirable effects of vortex shedding from cylinders immersed in uniform turbulent streams have been recognized, efforts have been directed towards finding practical means for controlling this phenomenon in order to reduce the magnitude of the fluctuating lift and drag forces on the cylinder. Choi et al. (2008) present an excellent review of methods for vortex shedding control. These fall into one of two categories - passive or active – depending on whether external energy is needed to operate them. Passive control methods include surface roughness (Zdravkovich, 1990; Shih et al., 1993; Perry et al., 1987; Adachi, 1997), the attachment to the cylinder surface of helical strakes (Lee & Kim, 1997) or splitter plates (Roshko, 1954; Bearman, 1965; Kwon & Choi, 1996), or by the placement of a small control cylinder in the cylinder wake (Strykowski & Sreenivansan, 1990). Active control methods include streamwise or transverse cylinder oscillations (Blackburn & Henderson 1999; Cetiner & Rockwell 2003), base-flow blowing or suction in either steady mode (Fransson et al., 2004) or periodically (Biringen, 1984). The case of steady blowing through a perforated surface of a square cylinder was studied experimentally by Cuhadaroglu et al. (2007) who found that the drag coefficient increases with the blowing rate when either the front or side surfaces were perforated but decreases when the perforation were to the rear. Dong et al. (2008) found that, for a circular cylinder, combined suction from the windward side and blowing from the leeward side produced marked reduction in the magnitude of the fluctuating lift. A similar outcome was obtained by Skaugset and Larsen (2002) and by Lin et al. (1995) by introducing the jets radially in the form of a helix. The use of jets to control vortex shedding was applied to geometries other than circular cylinder. Aydin et al. (2010), for example, found that vortex shedding from a square cylinder can be suppressed by means of jets self-issuing into the base flow. This mechanism was achieved by means of arranging for the incident flow to pass through the cylinder via channels that connect the stagnation line with the cylinder base.
