Control of Aeolian tones from a circular cylinder using forced oscillation

Effects of forced transverse oscillation on the generation of sound from a circular cylinder immersed in uniform flow at a Reynolds number 150 and a Mach number 0.2 is investigated by direct numerical simulation. The cylinder is prescribed to oscillate sinusoidally with a constant oscillating amplitude ratio α of 0.2 of the cylinder diameter and oscillation frequency ratios F=0.2 to 1.4 of the inherent vortex shedding frequency. The impact of the oscillating frequency on the sound pressure is in accordance with that of the forces acted on the cylinder, by which three regimes are identified. In the first regime (F≤0.7), the sound levels are slightly affected by the oscillation. In the second regime, at 0.8≤F<1.0 when the vortex shedding is entrained, an apparent reduction of sound pressure is achieved, together with a change in acoustic directivity; at 1.0≤F≤1.05, the sound generation is enhanced. In the third regime (F≥1.1), the sound level further increases with increasing F, and the sound field recovered has a lift dipole character. The variation of the sound generation and propagation nature can be demonstrated by the interaction of the lift dipole and drag dipole.