Abstract
Vortex drop shafts are special manholes designed to link sewer channels at different elevations. Significant energy head dissipation occurs across these structures, mainly due to vertical shaft wall friction and turbulence in the dissipation chamber at the toe of the shaft. In the present study two aspects, sometimes neglected in the standard hydraulic design, are considered, namely the energy head dissipation efficiency and the maximum pressure force in the dissipation chamber. Different physical model results derived from the pertinent literature are analyzed. It is demonstrated that the energy head dissipation efficiency is mostly related to the flow impact and turbulence occurring in the chamber. Similarly to the drop manholes, a relation derived from a simple theoretical model is proposed for the estimation of the energy head loss coefficient. The analysis of the pressures measured on the chamber bottom allows to provide a useful equation to estimate the pressure peak in the chamber as a function of the approach flow energy head.
Highlights
The recourse to sewer drop structures to convey water discharges from an upper elevation to a lower one has been well known for more than 30 years [1,2,3]
The inlet device consists in a tangential inlet or in a spiral inlet device, in which the approach flow is abruptly deviated towards the shaft and it assumes the typical helicoidal flow with a stable air core
The experiments analyzed all refer to a standard vortex drop shaft layout, with a free-surface inlet channel linked to the inlet device, a vertical shaft with a variable length, a dissipation chamber and an outlet tunnel
Summary
The recourse to sewer drop structures to convey water discharges from an upper elevation to a lower one has been well known for more than 30 years [1,2,3]. The main difference between the two consists in the flow behaviour at the top of the shaft. In plunging drop structures the incoming flow is issued from the inlet channel to the vertical shaft without any control. In vortex drop shafts a swirling motion is, instead, imposed to the approach flow by a specific inlet device placed above the shaft. Over the following years different drop structure layouts have been proposed [6,7,8,9,10]. The research on the optimization of the flow behaviour in such structures is still in progress, being motivated by the urgent necessity to carry rainwater discharges in deep tunnels and storage basins to prevent urban floods [11]
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