Developing flow in skimming flow regime on embankment stepped spillways

Abstract

In hydraulic engineering, stepped spillways are effective structures in regard to both energy dissipation and re-aeration processes. It is well known that flow depths and flow velocities generally depend on the spillway geometry in terms of slope and step-induced macro-roughness height on the one hand and the discharge on the other hand. Moreover, these parameters affect the air entrainment process and hence, the amount and the size of entrained air bubbles which are directly linked to the specific air–water interface being of particular significance for oxygen transfer. In this study, physical model investigations on a stepped spillway scaled 1:10 of varying step height, chute angle and discharge are conducted with the objective to analyse the development of these air–water flow properties in the non-uniform flow region. Measurements of air–water mixture velocity and air concentration are carried out by the use of an intrusive double-tip conductivity probe. It is found that the step-induced macro-roughness has a differing effect on particular flow characteristics.