Experimental analysis of water cushions, flow rate, and sediments impacts on the specific energy of flow in a vortex drop shaft

Vortex drop shafts are used in urban wastewater collection and drainage to transfer flow from high levels to low levels. In the present study, experimental investigations were conducted on a vortex drop shaft with a screw inlet. Weir, venturi and sump elements were used to improve the effectiveness of the dissipation chamber. The effects of sediments and flow rate on the effectiveness of the dissipation chamber was investigated. In evaluating the effectiveness of the dissipation chamber, an increase in the specific energy of the flow in the subcritical flow was considered a favorable factor, while an increase in the specific energy of the flow in the supercritical flow was considered as an unfavorable factor. The results showed that the dissipation chamber using sump, venturi, and weir elements, respectively, was more effective than without elements; so that the effectiveness of the dissipation chamber with the sump with hS/D=1 increased between 15.05 and 82.78%. Among the sediment sizes tested, the greatest impact on dissipation chamber effectiveness occurred with the D50 = 2.20 mm sediment, at low flow rates in conjunction with the taller weir and deeper sump configurations. The effect of sediments on the effectiveness of the dissipation chamber was eliminated by increasing the flow rate. Furthermore, analysis of variance was used to develop nonlinear models that showed satisfactory agreement with the experimental data, supporting their use for predictive purposes.