Tornado vortices in settling tanks

Settling tanks are hydraulically designed on a settling velocity. Observati ons have indicated that out-of-the-basin sediment transport may be initiate d by corner vortices, which are able to scour a sediment layer and signific antly reduce the efficiency of sediment deposition. Using four different ma terials-with densities from close to water up to sand, and diameters from 0 .55 to 3.0 mm-the various forms of vortex scour were experimentally determi ned. The densimetric particle Froude number could be identified as the scal ing quantity that governs these processes. The scour process can be reduced by inserting so-called antivortex elements, by which the 3D corner flow ch aracteristics are influenced to result in a more 2D flow over a wall. The l ocation and length of these elements were found to be similar to elements r ecently recommended for standard gates.