Vortex drop shaft for supercritical flow

Vortex drop shafts are used in urban drainage systems to connect two sewers located at considerably different elevations by means of a vertical conduit. The vortex drop shaft was first designed by Drioli (1947). It was then studied by other authors with reference to subcritical approach flow. Vortex shafts specifically conceived for supercritical flow can also used, but at very high costs due to the specially features required for the intake structure. The present study shows the experimental results of a specific investigation into the changes to be made in the approach channel for supercritical flow, when a subcritical vortex intake is used. The proposals concern the definition of the height of the step to be located in the approach channel, and the length of the lower-bottomed section in the approach channel, while maximizing the hydraulic efficiency of the system. Proper step height will cause the hydraulic jump to conveniently occur downstream of the step, whereas a regular subcritical flow in the intake structure of vortex shaft will result from lowering the bottom of the approach channel for the appropriate length.