Anti-vortex devices: laser measurements of the flow and functioning

Intake vortices are free surface vortices which are generated overhead a discharging orifice in a vessel; their occurrence is typical whenever the submergence is less than a critical value. If a vortex occurs,anti-vortex devices are used to avoid its negative effects. A new funnel-shaped device is presented herein whose lateral shape is the locus of the inflection points in the vertical profile of radial velocities. The inflection points were calculated on the basis of a new analytical solution that is capable of describing the bottom radial jet. Flow velocities are very small and have been measured by the PTV (particle tracking velocimetry) technique, which is based on a laser-optics implementation; the measured velocities compared well with the velocities computed by the analytical model. Since the funnel device is open (it has neither top nor bottom lids), it cannot inhibit vorticity stretching due to the axial flow; nevertheless, the experiments herein reported have proved the successful performance of the funnel device in preventing intake vortices, provided it is located with extreme accuracy. The funnel device turned out to perform surprisingly much better than the Prosser disk, whose shape is very different and, at least in principle, should be more effective than the funnel.