We present here experimental results and theory on the flow of an incompressible fluid (water) in a two-dimensional closed channel with an oscillating asymmetric constriction (Fig. 1). The motion of the constriction models the large amplitude self-excited oscillations that arise when fluid flows through a collapsible tube such as a vein1,2. Downstream of the oscillating constriction, a train of waves appears in the core flow and a double row of eddies forms along the channel walls (Fig. 2). This phenomenon, which occurs at all but the lowest frequencies, has not previously been observed. Our theory explains the occurrence of the wavetrain and accurately predicts several of its properties.
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