Air Entrainment and Air Demand in the Spillway Tunnel at the Jinping-I Dam

Jijian Lian,Wenjuan Gou,Shunqi Pan,Chunfeng Qi,Qunan Ouyang,Fang Liu

doi:10.3390/app7090930

Abstract

Artificial air entrainment has been widely used to avoid cavitation damage in spillways where high-velocity flow occurs, and its performance is very important for spillway safety. In order to evaluate the performance of the aeration system in the spillway tunnel of the Jinping-I Dam, which is the highest arched dam in the world to date, systematic prototype observation was conducted. Ventilation characteristics of the air supply system and aeration-related characteristics of the aeration devices were examined at the prototype scale. The results showed that air flows smoothly in the air intake well and the real effect of air entrainment of the aeration device was desirable. In contrast with results from laboratory tests with a physical model at a scale of 1/30 following the gravity similarity, it was found that air demand in the prototype is much greater, clearly indicating the scale effect. By summing up and analyzing the air demand ratio of the prototype to the model in some projects, the scale effect was found to be ignorable when the model scale was greater than 1/10. In addition, based on a series of prototype data on air demand, a brief evaluation of present calculation methods for air demand was conducted and a new form of calculation method for air demand related to unit width flow rate was established. The present prototype results can be used as a reference for similar engineering design, and to validate and verify numerical simulations as well as model tests.

Highlights

High-velocity flow often occurs on spillways, for high dams, which can cause severe cavitation damage to the hydraulic structures
Thereafter, the majority of air is discharged through the water-free space of the spillway tunnel, and only a small amount of air is entrained into the water body by means of cavity artificial aeration and surface self-aeration
As aerated air through cavity aeration experiences a motion trace—firstly, air is sucked into air intake well, flows past the air duct and enters into the cavity, entrained into the high-velocity water flow —the results are presented in this order

Summary

Introduction

High-velocity flow often occurs on spillways, for high dams, which can cause severe cavitation damage to the hydraulic structures. Some measures, such as optimizing the structure body, smoothening the concrete surface, and applying anti-cavitation materials are commonly implemented to prevent the cavitation, but the potential damage cannot be completely eliminated. Engineering experiences show that artificial air entrainment is an economical and effective way to protect the concrete surface from cavitation damage by means of setting auxiliary devices on the bottom of spillways and sometimes on sidewalls [1,2,3,4,5]. Russell [9] suggested that the critical air concentration to avoid cavitation damage is 2.8%

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