An improved air entrainment model for stepped spillways

Silje Kreken Almeland,Timofey Mukha,Rickard E Bensow

doi:10.1016/j.apm.2021.07.016

Silje Kreken Almeland, Timofey Mukha + Show 1 more

Open Access

https://doi.org/10.1016/j.apm.2021.07.016

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Abstract

This work considers the application of the air entrainment model developed in [P. Lopes et al. Int. J. Nonlin. Sci. Num., vol. 18, pp. 559-574, 2017] to simulation of flows in stepped spillways. Four Froude numbers are considered for the flow, with parameters selected to match available experimental data. An extensive simulation campaign led to the identification of several deficiencies in the model, most importantly, its strong grid dependence. An improvement to the interface detection algorithm used in the model is proposed, and simulations reveal improved robustness with respect to the grid density. Furthermore, two criteria for predicting the inception point of air entrainment are tested, based on energy balance and boundary layer state, respectively. The boundary layer-based approach is recommended due to superior accuracy and robustness with respect to turbulence model selection.

Highlights

Along with a renewed interest in stepped spillways as a flood overflow structure and energy dissipator in hydraulic engineering, attempts at gaining a better physical description of spillway flows have intensified
It has since the early work of Straub and Anderson [26] been widely accepted that the onset of self-aeration takes place when the turbulent boundary layer, developed from the crest, reaches the free surface
This study presents developments in numerical modelling of self-aeration in stepped spillways

Summary

Introduction

Along with a renewed interest in stepped spillways as a flood overflow structure and energy dissipator in hydraulic engineering, attempts at gaining a better physical description of spillway flows have intensified. Air entrainment is driven by turbulent motion and occurs when the turbulent forces at the free surface overcome the stabilizing effects of surface tension and buoyancy [10] Applied to spillways, it has since the early work of Straub and Anderson [26] been widely accepted that the onset of self-aeration takes place when the turbulent boundary layer, developed from the crest, reaches the free surface. It has since the early work of Straub and Anderson [26] been widely accepted that the onset of self-aeration takes place when the turbulent boundary layer, developed from the crest, reaches the free surface This location is commonly referred to as the ‘inception point’. Several contributions consider the onset of the aeration in detail [6; 33; 28], and empirical relations exist for the distance to the inception point from the spillway crest

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