On the incipient aerated flow in chutes and spillways

Abstract

Natural self-aeration of water flows in open channels protects surfaces in contact with the flow from cavitation damage if enough air content is reached (Falvey [6] [7], Peterka [10], Russel & Sheenan [11]), although it could lead to an increase in both flow depth and velocity. Also, self-aerated flow enhance the process of atmospheric gases exchange within the fluid, improving water quality downstream of hydraulic structures (Chanson [5]). So it is of great interest to evaluate accurately the critical point where air entrainment begins, that is, the location of the inception point. The note first shows a review on some methods to evaluate the inception point location. Second, a brief explanation on calculation development is made and an expression is obtained which enables to compute the point of incipient self-aeration as a function of unit discharge, bottom slope of the chute and uniform surface roughness in a more simple and accurate way. Finally, comparison with results provided by other methods is made and conclusions are obtained. RÉSUMÉ L'auto aeration de l'eau dans les canaux a ciel ouvert protege les surfaces en contact avec l'écoulement, des dommages dus a la cavitation, s'il y a suffisamment d'air (Falvey [6] [7], Peterka [10], Russel & Sheenan [11]), bien que cela puisse conduire a un accroissement de la hauteur d'eau et de la vitesse. L'auto aeration renforce également le processus d'échange des gaz atmosphériques au sein du fluide, ce qui améliore la qualité de l'eau a l'aval des ouvrages hydrauliques (Chanson [5]). Il est done fort interessant d'évaluer avec précision le point critique du début d'entrainement d'air, e'est-a-dire la localisation du point d'amorcage. Cette note présente d'abord quelques methodes pour évaluer la position du point d'amorcage. On explique ensuite brièvement le développement du calcul puis on obtient une expression qui permet de calculer le point d'amorjage de l'auto aeration en fonction du débit, de la pente du fond et de la rugosité uniforme de surface, d'une maniere plus simple et precise. Finalement, on effectue une comparaison avec les résultats fournis par d'autres methodes, et l'on en tire des conclusions.

Experimental Analysis of the Influence of Aeration in the Energy Dissipation of Supercritical Channel Flows

“…Results obtained during the experimental another coalysis of the spillway channel show a flow velocity increase with higher concentration. This phenomenon has been described before by Moñino [9] and Kramer [10]. Moreover, several studies have analyzed the effect of emulsionated flows in spillways with artificial aeration, as in Luna-Bahena [11] and Koen [12].…”

A Brief Theoretical Analysis on the Ventilation Characteristics of the Multi-Intake-Well Air Supply System in a Spillway Tunnel

“…Cavitation damage is a common problem of high-velocity water in hydraulic engineering [1][2][3]. An economical and effective solution to reducing the possibility of cavitation is to aerate the water flow [4][5][6][7][8].…”