Energy Dissipation of Flow in the Vortex Structure: Experimental Investigation

With the rapid rise in the development of urban districts, a ferocious demand for water-collecting urban sewer systems is inevitable. In fact, flexible sewer collection systems and drainage systems should be developed for controlling sewage and runoff, respectively. In the case of underground sewers, conducting water flow properly through high vertical distances needs reliable criteria design for dissipating flow energy. Vortex structure is taken into account as one of the economical infrastructures that can be used to eradicate destructive impacts of inflow over a drop with invert elevation. In the current investigation, a physical model, made of Plexiglas segments, was set up to study hydraulic performance of the vortex drop structure with tangential inlet in terms of flow energy dissipation efficiency (FEDE). A total of 144 experiments were conducted and analyzed by means of the full factorial method (FFM). Results of dimensional analysis demonstrated that Froude number ($F_r$), ratio of drop total height to shaft diameter ($L/D$), and ratio of sump depth to shaft diameter ($H_s/D$) were considered effective variables on FEDE. Furthermore, a regression-based equation in the form of a quadratic polynomial was proposed to estimate the FEDE variable. Experimental aims were to investigate the simultaneous effects of approach flow $F_r$, $L/D$, and $H_s/D$ on the FEDE. Results of experiments indicated that the FEDE variable had downward trends with an increase in the $F_r$ variable, and additionally FEDE has gone through upward trends with an increase of $L/D$ and $H_s/D$ ratios. Furthermore, an interaction effect of $F_r$ and $H_s/D$ on the FEDE variable remained meaningless. Ultimately, the sump depth at the base of the drop shaft for 1–1.6 times the diameter was recommended for getting efficient performance of the vortex structure.