Controlling sound radiated from a circular cylinder undergoing vortex-induced vibration via synthetic jets

The effect of a pair of synthetic jets (SJs) on sound generation from a circular cylinder undergoing vortex-induced vibration (VIV) is numerically investigated under two-dimensional conditions. The cylinder is immersed in a uniform flow and vibrates in the transverse direction at a Reynolds number of 150 and a Mach number of 0.05. Various frequencies ( f s j * ) and phase differences ( Δ ϕ ) of SJs are employed to examine their impact on far-field sound radiation. The modulation of VIV and flow structure by SJs also affect the sound generation and propagation. Anti-phase SJs can sufficiently suppress the intensity of the lift dipole and the drag dipole by 85% and 75%, respectively, while the drag dipole dominates the sound field. Through the dynamic mode decomposition analysis for the spatial distribution of components associated with various frequencies, the sound generation mechanism is revealed. The adverse effect of SJs has been attributed to the amplification of the harmonic component and self-noise generated from SJs due to a non-zero mass flow rate or injection of momentum flux. And combining with the acoustic analogy equation, these mechanisms of sound generation are first determined in two-dimensional conditions. Consequently, SJs can efficiently reduce the sound radiation by suppressing VIV. However, their disadvantages, including self-noise generated by SJs and the increased high-frequency components, have also been emphasized.