Author(s): Weichen Ren, Jianhua Wu, Fei Ma
Keywords: Urban storm-water projects; Helical-step dropshaft; Flow regimes; Energy dissipation; Air concentration;
Abstract: Due to large flow discharge and high-speed flow, energy dissipation and cavitation damage prevention are a serious concern in the design of dropshafts. In the present work, a kind of helical-step dropshaft was developed, which consists of an air vent pipe at the center of the dropshaft and a continuous so-called helical stepped chute attached to the wall. The experiments were therefore conducted on the hydraulic characteristics of helical-step dropshaft, including the observation of flow regimes, the measurements of energy dissipation ratio and air concentration in vertical and horizontal surfaces in the steps. And the experimental results demonstrate that water can be conveyed by the helical-step dropshaft smoothly and steadily, with the prototype discharge up to 45 m3/s in the present experiment; the energy dissipation of the helical-step dropshaft decreases with increasing discharges, but still exceeds 85.0 % for the maximum discharge; and the proposed dropshaft enjoys few cavitation risk on the basis of a minimum air concentration measured. It is believed that this study provides a new idea for the design of shaft structure in urban deep tunnel drainage system.