AERODYNAMIC NOISE GENERATED BY 2 CIRCULAR-CYLINDERS ARRANGED IN TANDEM

The aerodynamic noise generated by two circular cylinders with differe nt diameter ratios arranged in tandem has been investigated experiment ally. In this study the diameter ratio d/D is smaller than or equal to 1, where d and D are the diameter of the upstream and downstream cyli nders. Two major components were identified in the nose: one is the no ise associated with vortex shedding from the cylinders (the vortex-she dding nose) and the other is the interaction noise due to the vortices impinging on the downstream cylinder. The level of the vortex-sheddin g noise from the upstream cylinder changes periodically if it is plott ed against the spacing L, between centers of the cylinders, whereas it s frequency increases asymptotically to the vortex-shedding frequency of the single cylinder in a uniform flow with increasing L. The wavele ngth of the periodicity was found to be associated with the distance b etween neighboring vortices shed from the upstream cylinder. On the ot her hand, the frequency of the vortex-shedding noise from the downstre am cylinder is reduced by the effect of the wake of the upstream cylin der. An interaction noise was found to exist; its frequency was determ ined by the distance L and the free-stream velocity in the same manner as that of a self-sustained oscillating flow.