Hydraulic performance of helical-step dropshaft

Abstract

Aiming to achieve energy dissipation and prevention of cavitation erosion, a kind of dropshaft in urban drainage systems, called helical-step dropshaft, is introduced in this paper. It dissipates flow energy by means of step geometry and prevent cavitation erosion through air entrainment. To verify its availability, the hydraulic characteristics of the helical-step dropshaft were experimentally investigated, including the flow regimes, the efficiency of energy dissipation, characteristics of air entrainment and pressure distribution. The results demonstrate that, even for a large discharge, flow can be discharged smoothly and steadily, and a high energy-dissipation rate of over 87% is achieved. There are three distinct flow regimes observed in the dropshaft, namely nappe flow, mixed flow and skimming flow. Moreover, there is no less than 1.6% air concentration and a reasonable pressure distribution on the step surface. This study provides an attractive alternative for the design of drop structures.

Effects of Converging Sidewalls on Skimming Flow over Converging Stepped Spillway

“…The hydraulic performance of the air-water flow over the steps is affected and complicated by sidewall convergence in converging stepped spillways. One typical flow phenomenon occurring on the converging stepped spillways is the creation of standing waves near the sidewalls, especially during the skimming flow regime [11][12][13][14][15]. Hunt et al [13] experimentally measured the depth of standing waves over a converging stepped spillway with a mild bottom slope of θ = 18.4 • and found when the sidewall convergence angle Φ = 15 • , 30 • and 52 • , the maximum standing wave depth can reach 1.0h c , 1.75h c and 3.0h c , respectively.…”