Author(s): Matthias Burgler; Daniel Valero; David. F. Vetsch; Robert M. Boes; Benjamin Hohermuth

Linked Author(s): Robert Boes

Keywords: Spillway flow; Self-aeration; Two-phase flow; Phase-detection probe; Bottom air concentration

Abstract: Spillways are critical appurtenant structures of reservoir dams, designed to prevent uncontrolled overtopping during extreme flood events. The highly turbulent nature of free-surface flows on spillways typically results in entrainment of air, forming a chaotic air-water mixture flow. The accurate description of such flows for a range of chute slopes, invert roughness heights and flow conditions, remains a challenging task. This is mainly limited by the availability of comprehensive, temporally and spatially highly resolved data sets from large-scale physical models or prototypes. In this work, we address this knowledge gap by measuring air-water flow properties on a large-scale smooth spillway chute using phase-detection probes. A particular focus is set on the effect of invert roughness in the developing aerated flow region. Therefore, two different sand roughness heights were tested, resulting in hydraulically rough conditions, representative of most prototype conditions and something that was typically not achieved by most previous model studies. The results indicate that invert roughness can affect bottom air concentrations and flow velocities, while no apparent effect on mean bubble size distributions across the depth were observed. Overall, these laboratory experiments contribute to an improved description of the physical processes characterizing self-aerated flows in the developing aerated flow region on spillways and thereby can contribute to the development of physically-based predictive models.

DOI: https://doi.org/10.3850/978-90-833476-1-5_iahr40wc-p0509-cd

Year: 2023