Experimental Characterization of Air Entrainment in Rectangular Free Falling Jets

José M Carrillo,Juan T García,Patricio R Ortega,Luis G Castillo

doi:10.3390/w12061773

José M Carrillo, Juan T García + Show 2 more

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https://doi.org/10.3390/w12061773

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Abstract

This experimental study presents an analysis of the air–water flow in rectangular free-falling jets. The measurements were obtained downstream of a 1.05 m wide sharp-crested weir. The properties of the air–water flow were registered in several cross-sections of the nappe. A conductivity phase detection probe was employed, sampling at 20 kHz. Three different specific flows were considered, with energy head over the crest of 0.080, 0.109 and 0.131 m to avoid scale effects. To analyze the flow properties, air–water parameters during the fall, such as the phase change spatial distribution, air–water phase change of frequency, Sauter mean diameter, bubble chord length, turbulent intensities and spectral analyses, were studied. The jet thickness behaviors (inner jet core and free surface) were also analyzed in the falling jet. The jet thickness related to a void fraction of 90% seems to be similar to the theoretical proposal obtained by Castillo et al. (2015), while the jet thickness related to a void fraction of 10% seems to be similar to the jet thickness due to gravitational effects. The results show relative differences in the behavior of the upper and lower sides of the nappe. The experimental data allow us to improve on and complement previous research.

Highlights

The increase in the magnitude of design floods at large dams around the world and the new regulations in demands have driven a more rigorous assessment of the spillways’ capacity and their use in normal and extraordinary operating scenarios
The inlet channel ends in a sharp-crested weir without lateral contractions, located at an elevation of 2.20 m above the bottom of the plunge pool
Free surface aeration in rectangular free-falling jets may be considered an effect of the surface instabilities and turbulent fluctuations which act on the upper and lower free surfaces of the nappe jets

Summary

Introduction

The increase in the magnitude of design floods at large dams around the world and the new regulations in demands have driven a more rigorous assessment of the spillways’ capacity and their use in normal and extraordinary operating scenarios. Given the current capacity of many spillways, their discharge capacity may be inadequate in extreme operating scenarios. During these events, dams may overflow, compromising their stability and safety Emergency Management, FEMA [1]) In some cases, such as extreme events and/or in emergency scenarios, the overflow may be considered as an extra discharge operation. This situation creates new questions about the actions at the dam toe and in the regulation structures of the dams (Wahl et al [2]). It is necessary to evaluate these considerations and propose viable technical/economic solutions

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