Interference between stationary and vibrating cylinder wakes

The flow behind two side- by- side tubes of identical diameter, d, one stationary and the other forced to oscillate in the lateral direction at an amplitude of A = 0.1 similar to 0.5d was examined. Two values of T/ d, i. e., 2.2 and 3.5 were investigated, where T is the cylinder center- to- center spacing. The Reynolds number Re ranges from 150 to about 1000. The effect of A/ d, T/ d, and f (e) / f (s), where f (e) is the cylinder oscillating frequency and f (s) is the vortex shedding frequency of an isolated stationary cylinder, on the vortex shedding and the wake structure was examined. Specific attention was given to the occurrence of lock- in, where vortex shedding from the oscillating cylinder synchronizes with f (e). Significant influence of these parameters has been observed on the flow behind the cylinders in terms of the predominant vortex patterns and interactions between vortices. It has been found that the shedding frequency associated with the oscillating and the stationary cylinder can be modified as f (e) / f (s) approaches unity. Furthermore, the flow regime may change under the conditions of T/ d = 2.2 and A/ d = 0.5 from two distinct coupled streets to the combination of one narrow and one wide street. Subsequently, the lock- in state is considerably extended probably because multiple dominant frequencies in the asymmetrical flow regime can all be locked in with the structural oscillation. (C) 2003 American Institute of Physics.