The wake of a transversely oscillating circular cylinder in a flowing soap film at low Reynolds number
Wenchao Yang, Emad Masroor, and Mark A. Stremler
J. Fluids Struct., Aug 2021
An inclined gravity-driven soap film channel was used to study the wake patterns formed behind a transversely oscillating cylinder at Re=235±14. The natural frequency of vortex shedding from a stationary cylinder, fSt, was used to identify the oscillation frequencies of interest. The (dimensionless) frequency, f∗=f∕fSt, and amplitude, A∗=A∕D, of the cylinder’s motion was varied over a large portion of the fundamental synchronization region (i.e., for f∗≈1), and a ‘map’ of wake patterns was constructed in (f∗,A∗) space. Lock-on between the frequency of the cylinder’s motion and the dominant frequency of the resulting vortex wake was observed for a large range of this parameter space, predominantly manifested as synchronized ‘2S’ and ‘2P’ wake modes. Synchronized ‘P+S’, ‘2T’, and ‘transitional’ wakes were also found in smaller regions of parameter space. Unsynchronized ‘coalescing’ and ‘perturbed von Kármán’ wakes were observed as the oscillation frequency became sufficiently different from fSt. The wake patterns and vortex formation processes found in this study, particularly the 2P mode wakes, bear a strong resemblance to previous three-dimensional experimental results, despite the physical constraint from the soap film that limits three-dimensional effects in the wake.