Author(s): H. Cui; S. Felder; M. Kramer

Linked Author(s): Matthias Kramer

Keywords: Grass-lined spillway; air entrainment; non-intrusive sensing technology; acoustic displacement meter; entrapped air; interface frequency

Abstract: Grass-lined spillways constitute an environmentally friendly alternative to conventional concrete structures with flat slope and therefore may contribute to water-sensitive urban design. Research into supercritical self-aerated flows down grass-lined spillways has commenced recently, but important knowledge gaps related to air entrainment, flow resistance and bubble-canopy interaction are yet to be filled. This study presents first results of an experimental investigation into flows over a rough grass-lined channel bed with embankment slope. The deployed measurement instruments included acoustic displacement meters (ADMs) and a conventional intrusive phase-detection probe. A transformation of measured free-surface elevations into multiple time series of instantaneous air concentrations allowed to non-intrusively compute air concentration distributions, dimensionless interface frequency distributions, and chord times. The results demonstrated that the amount of entrapped air was significantly larger than the amount of entrained air. It was further shown that air concentration distributions followed a recently developed semi-analytical solution with a characteristic length that was closely linked with the mean air concentration. The ADM measurements were limited to entrapped air and future research should explore other non-intrusive instrumentation to also explore measurements of entrained air.

DOI: https://doi.org/10.26077/24ae-7606

Year: 2022