Abstract. The interaction of two-dimensional vortex flows with a free surface is studied numerically using a combined vortex/boundary integral technique. The vorticity is modeled as point vortices, vortex sheets and finite area vortex regions. Two
Two vertical, rotating flaps are used to generate a vortex pair beneath a free surface. Vortex pair formation, propagation, and interaction with a free surface are described. Numerical simulations for inviscid flow about a constant upwash sheet of vorticity beneath a free surface agree with experiment up to the time that turbulent mixing occurs during interaction with the free surface. The spacing between the vortex pairs then becomes larger than the calculated spacing. The experiments and lines of marked particles included in the simulations show fluid ingestion and transport toward the free surface.
A number of experiments were performed with water jets discharging into air to determine the effect of the initial velocity profile on the contiguous length of the water stream. This investigation was the consequence of noting that the usual analyses of the stability of such jets assumes an initially constant axial velocity distribution. The results show that the disturbance growth rate for an initially parabolic axial velocity profile is considerably less than that for a nearly uniform profile. This result differs from some other work that concluded the parabolic profile to be the more unstable. The results of the experiments are supported, in part, by an asymptotic analysis of the flow.
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