Effects of Two In-Phase Operating Synthetic Jets Ejected Transversely on Two-Degree-of-Freedom Vortex Induced Vibrations of a Circular Cylinder

Abstract

The impacts of two synthetic jets ejected transversely on two-degree-of-freedom vortex induced vibrations (VIVs) of a circular cylinder with the mass ratio m* = 5.78 in turbulent flow are numerically studied. Synthetic jets are placed on the upper and lower shoulders of the cylinder, and the momentum coefficient C_u is equal to 1.0, 2.0, and 4.0, respectively. The Reynolds number of uniform free-stream flow varies between 1803 and 7212, corresponding to the reduced velocity range 3.0 ≤ U* ≤ 12.0. The oscillation characters, the hydrodynamic force coefficients, and the wake structures are compared and analyzed in various cases. The results indicate that the synthetic jets could enhance both streamwise and transverse oscillations of the cylinder at U* ≥ 6.0, and the strengthening effect on oscillations is improved with increase in C_u. In the controlled cases, the synchronization region of the transverse oscillations is extended, and the streamwise oscillation frequencies are close to  f_{n, x}  at the most reduced velocities. The “dual-resonance” phenomenon is observed at C_u = 4.0 when 3.0 ≤ U* ≤ 8.0. The synthetic jets could promote vortex shedding on the cylinder’s shoulders, and the 2S mode, the 4P mode, the special 2S mode (with additional small vortex pairs), and the 2P + 2S mode are observed in the controlled cases. Vortex shedding is unstable in some special cases, which cause the appearance of abnormal oscillation behaviors and irregular oscillation trajectories.