Active cancellation of sound generated by finite length coherent line sources using piston-like secondary source arrays

The active cancellation of the sound generated by finite length coherent line sources is investigated numerically in the present study. A secondary source consists of a central circular core enclosed within an annulus is proposed. It is demonstrated that this source type can produce a much more directional secondary sound field than a single circular piston, even its size is much smaller than the latter if its two parts are vibrating out-of-phase with the right magnitude ratio. This property gives rise to more effective spanwise sound reduction. An example of a secondary source array for broadband noise control is also provided. Though the control performance becomes weaker as frequency increases, the noise reduction within the central region of the receiver plane remains significant in all the cases included in the present study.