  Oscillatory flow in confined spaces is central to understanding physiological
flows and rational design of synthetic periodic-actuation based micromachines.
Using theory and experiments on oscillating flows generated through a
laser-induced cavitation bubble, we associate the dynamic bubble size (fluid
velocity) and bubble lifetime to the laser energy supplied - a control
parameter in experiments. Employing different channel cross-section shapes,
sizes and lengths, we demonstrate the characteristic scales for velocity, time
and energy to depend solely on the channel geometry. Contrary to the generally
assumed absence of instability in low Reynolds number flows (<1000), we report
a momentary flow distortion that originates due to the boundary layer
separation near channel walls during flow deceleration. The emergence of
distorted laminar states is characterized using two stages. First the
conditions for the onset of instabilities is analyzed using the Reynolds number
and Womersley number for oscillating flows. Second the growth and the ability
of an instability to prevail is analyzed using the convective time scale of the
flow. Our findings inform rational design of microsystems leveraging pulsatile
flows via cavitation-powered microactuation.
