Noise reduction by feedback rotary oscillation of a three-dimensional circular cylinder

The sound generation by a three-dimensional circular cylinder in a uniform flow is numerically studied at Mach number of 0.2 and Reynolds number of 1000. The primary motivation is to study the effect of feedback rotary oscillation on the flow control and noise reduction. The flow control strategy is to force the cylinder to rotationally oscillate about its axis with [Formula presented], where [Formula presented], is the instantaneous angular speed of rotation cylinder, λ is control parameter and C_z, is the feedback signal of lift coefficient. First, the sound pressure level and frequency of fundamental peak of a stationary cylinder are well predicted by the present numerical model. The aerodynamic sound is found to be mainly dependent on the spanwise vortices shed from the cylinder. Further, the numerical results show that the amplitude of fluctuating lift is significantly reduced by the feedback rotary oscillation of cylinder. The near wake of cylinder is examined to show the effect of the active control method on the vortex shedding and lift fluctuation. Correspondingly, the noise from the cylinder can be reduced by 10 dB through the feedback rotary oscillation. The energy consumption corresponding to this active control method is discussed. It is shown that the feedback rotary oscillation might be a promising method to reduce the sound radiation from a cylinder in uniform flows.