Experimental analysis of a vertical drop shaft

An experimental campaign is undertaken in order to investigate the hydraulic features of a vertical drop shaft, also considering the influence of a venting system consisting of a coaxial vertical pipe, projecting within the drop shaft with different plunging rates. Three different flow regimes are observed: a “weir flow” for very low head values, where the flow profile is subject to the atmospheric pressure; a “full flow” for high head values, where water flows in a pressurized regime along the whole shaft; and a “transitional flow” for intermediate water head values. Weir flow and full flow can be experimentally investigated under steady-state conditions, whereas transitional flow is a pulsating condition, alternately switching from full flow to weir flow. Considering some significant geometric parameters, a head-discharge relation is sought both for the non-vented and for the vented configurations, by means of an energy balance equation, with specific assumptions about intake losses.