Flow patterns in a supercritical vortex drop shaft

Vortex drop shafts are special sewer structures through which a nearly horizontal free-surface flow is forced to rotate and turn into a swirling flow across the vertical shaft. The current design guidelines are lacking in indications about the velocity and pressure distributions across the vertical shaft. The present research, therefore, provides new experimental data related to the flow field establishing across the vertical shaft when the structure is approached by a supercritical flow. The study is based on a CFD modelling by carrying out 3D Volume-Of-Fluid numerical simulations. At this aim, the commercial software Flow3D was used. The experimental program was designed to observe the hydraulic features of the swirling flow by changing the flow discharge. The preliminary results are used to show that the flow behaviour inside the shaft varied depending on the capacity Froude number. In particular, two flow patterns are detected: the helical flow pattern and the annular flow pattern.