Author(s): Kavianpour M. R.; Masoumi H. R.
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Keywords: Spillway; Cascade; Aeration; Inception point
Abstract: Stepped spillways have been used as hydraulic structures to dissipate energy, to enhance aeration rate in the flow and also to comply with visual functions. They can be found acting as spillways in dams and weirs, as energy dissipators in artificial channels, gutters and rivers, and as aeration enhancers in water treatment plants. In recent years, new construction techniques and materials (RCC) together with the development of new applications have allowed cheaper construction of stepped chutes, increasing the interest in stepped chute design. One of the main tasks in the design of spillways is to determine the point of inception. At this point, the boundary layer meets the free surface and the turbulence initiates natural free-surface aeration, caused by turbulent velocities acting normal to the air-water boundary. Downstream of this point, a layer containing an air-water mixture forms, increasing in thickness with distance from the point of inception. Eventually, the flow becomes uniform, with air concentration and velocity distribution stable along the channel. This study consists of the experimental investigation of air-water flow on step spillways to determine the inception point of air entrainment. The study conducted at Water Research institute of Iran on two physical models belongs to Siyah Bisheh dam in central Iran. Various experimental information of previous studies have also been collected to cover a wide range of geometry and flow characteristics. The results were used to develop an expression to predict the inception point for air entrainment in skimming flow regime, which is very important in the process of energy dissipation and essential for the design of these structures.
Year: 2007