In this paper we present the results from numerical calculations,
based upon the
Navier–Stokes equations at relatively high Reynolds number, of the formation of
a vortex ring when fluid is ejected from a circular tube. Our results are
compared with the experiments of Didden (1979), and the inviscid flow calculations of
Nitsche & Krasny (1994). Reasonable agreement is achieved except for the rate of
shedding of circulation during the initial stages of ring formation. The
theoretically
predicted rate of shedding is substantially higher than that predicted by Didden. By
contrast the inviscid theory predicts an anomalously high rate of initial
shedding. We
offer explanations for both of these apparent discrepancies.