On the Coupled Dynamics of Wall-Mounted Flexible Plates in Tandem

The coupled dynamics of two rectangular, flexible plates of h/b (height/width=4) was experimentally explored in tandem arrangements under uniform flows at various Cauchy numbers (Ca) and spacings. Planar particle image velocimetry and particle tracking velocimetry were used to characterize the surrounding flow and dynamics of the structures. Results indicate that the motions of the upstream plate were governed by its natural frequency, whereas the oscillations of the downstream counterpart were highly modulated by the upstream wake. Such effect led to highly correlated motions between the plates with similar oscillation amplitude under relatively small spacing (0.5h), to comparatively larger amplitude of the downstream structure at intermediate spacing (1h), and nearly decoupled interactions with large gap (2h). Despite that the oscillation intensity of the upstream plate increased monotonically with Ca, this was not the case for the downstream plate at intermediate and large gaps; this resulted in a local minimum. A model is derived to explain this phenomenon, which accounts for the influence of wake fluctuation intensity, vortex shedding and large structure deformation.