INTERACTION OF A TURBULENT ROUND JET WITH THE FREE-SURFACE

The interaction of a turbulent round jet with the free surface was inv estigated experimentally. Flow visualization, free-surface curvature m easurements and hot-film velocity measurements were used to study this flow. It is shown that surface waves are generated by the large-scale vortical structures in the jet flow as they interact with the free su rface. These waves propagate at an angle with respect to the flow dire ction which increases as the Froude number is increased. Propagation o f the waves in the flow direction is suppressed by the surface current produced by the jet. Farther downstream the surface motions are cause d by the large-scale vortical structures. Characteristic dark circular features are observed in shadowgraph images associated with concentra ted vorticity normal to the free surface. The normal vorticity is beli eved to be the result of vortex line reconnection processes in the tur bulent flow. Measurements of the mean velocity and turbulence intensit y are reported. Owing to the confinement by the free surface, the deca y rate of the maximum mean velocity is reduced by a factor of square-r oot 2 compared to an unconfined jet.