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In this article, we investigate experimentally and numerically the timeevolution of vortex rings generated by the translation of a rigid disk in afluid initially at rest and submitted to an acceleration followed by adeceleration. The size of the disk and its motion in terms of stroke length andtravel time are varied as control parameters. The start-up vortex ring createdin the near wake of the disk is characterized experimentally by PIV, and themeasurements agree quantitatively with axisymmetric numerical simulationsperformed with the Basilisk flow solver. The maximum radius and circulation ofthe annular vortex and its dynamics are shown to follow different power lawswith the control parameters. The modeling adapted from Wedemeyer'stwo-dimensional theoretical calculations [E. Wedemeyer, Ausbildung einesWirbelpaares an den Kanten einer Platte, Ingenieur-Archiv 30, (1961)] capturesthe observed scaling laws. Besides, after the disk stops, a secondary``stopping" vortex ring is generated, which is shown to affect the motion ofthe main vortex ring.

Vortex rings generated by a translating disk from start to stop