Author(s): Hubert Chanson

Linked Author(s): Hubert Chanson

Keywords: Circular weirs; physical modelling; Froude similarity; non-linearities; scale effects

Abstract: Liquid overflowing over rounded weirs experiences a rapidly accelerating flow region with converging streamlines near the crest. Depending upon the discharge, radius of curvature and weir height, the overflow nappe may be attached or detached. Herein, detailed physical modelling was conducted under carefully controlled conditions with a circular weir equipped with a relatively small radius of curvature. The results highlighted a narrow range of hydrodynamic transient conditions for which both attached and detached nappe situations may co-exist, as well as partial nappe detachment conditions. The hydrodynamic processes presented some hysteresis and transients were observed as a result of non-linear instabilities during both detachment and re- attachment of the nappe. Scaling considerations are discussed based upon new physical experiments in facilities with different sizes. The outcomes are challenging and highlight the limitations of simplistic Froude similitude and the role of the pool of recirculating water at the weir toe.

DOI: https://doi.org/10.3929/ethz-b-000675921

Year: 2024