Amplitude modulation and suppressed shedding in the wake of a streamwise-oscillating cylinder*

In this study we investigate the development of amplitude modulation in the wake of a streamwise-oscillating cylinder. Our forcing regime consists of oscillation frequencies, f_f, much lower than corresponding shedding frequencies, f_s. In contrast to cases where these frequencies are of the same order of magnitude, our regime of interest has been relatively less studied. We combine experimental and theoretical approaches using particle image velocimetry and Koopman mode decomposition, respectively, to study frequency ratios in the range f_f / f_s ∼ 0.02-0.2 with mean Reynolds number, Re = 800. Although the amplitude of oscillation is such that the instantaneous Reynolds number is far from the critical value, a range of interesting phenomena appear in the wake, including amplitude modulation and periods of suppressed vortex shedding.