# Air Entrainment and Air Demand in the Spillway Tunnel at the Jinping-I Dam
## 5 Conclusions  
In this paper, results of prototype observation on air entrainment performance in the Jinping-I spillway tunnel were presented. Ventilation-related parameters (air velocity in air intake well, air-flow vibration noise) and aeration-related parameters (air velocity in air duct, cavity sub-pressure, air concentration close to tunnel bottom, cavitation damage depth of concrete surface and cavitation noise of flow) at five different flow rates (297, 791, 1462, 2130 and 3200 m\({}^{3}\)/s) were measured. Generally, air flows smoothly in the air intake wells, but high air velocity and loud noises are observed in some cases. Air velocity in the intake wells is in the range of 12-90 m/s, increasing with the increase of the flow rate in the spillway tunnel, but it may also be affected by spillway tunnel size when the flow rate is large enough. Fluctuating energy of air velocity is mainly concentrated in a low frequency domain (about 0-10 Hz), and its fluctuating intensity is about 5-17% when air is sucked into the air intake well smoothly. The corresponding noise caused by air fluctuation is in the range of 95 to 120 dB, such a level of noise is significant enough to cause instantaneous hearing loss. The overall effect of air entrainment of the aeration device was regarded as good, as no obvious damage to the concrete bed was found. Air velocity in air duct is in the range of 24-90 m/s, it increases with the increase of the flow rate, with a gradually reduced rate. Cavity sub-pressure varies from \(-\)6.26 to \(-\)15.77 kPa over the range of flow rates observed, and its dependence on flow rate is similar to that of air velocity. The attenuation rate of air concentration near the bottom is influenced by the chute slope, and is faster as the slope is greater. Relatively low air concentration (less than 3%) at the ends of protective range could also prevent concrete surfaces from cavitation damage. Damage depth of the concrete surface is slight (less than 5 cm), indicating that no significant cavitation occurred after applying aeration devices. In addition, by comparing the results from the prototype and laboratory experiments, it was found that there is an obvious scale effect on air demand and air concentration distribution. The results showed that only when the model scale is greater than 1/10 can the air demand in the model and prototype be similar. Due to the complexity of the air entrainment phenomenon, the present theoretical formula or empirical formulas for air demand calculation still cannot be universally used in all projects. Moreover, it is found that the air entrainment ratio and unit width flow rate in general follow the power-law. Accordingly, a new formula only related to flow rate and aerator device parameters and used for air demand calculation was established. To improve the estimation of air demand for the spillway tunnel, further studies should be centered on accurately simulating the flow turbulence level in laboratory model tests, and more systematic prototype observations are also required. The authors are grateful to the National Key R&D Program of China (2016 YFC0401904), Science Fund for Innovative Research Groups of the National Natural Science Foundation of China (51621092), Program of Introducing Talents of Discipline to Universities (B14012), Tianjin Research Program of Application Foundation and Advanced Technology (15 JCQNJC07100) and the Tianjin Innovation Team Foundation of Key Research Areas (2014 TDA001) for financial support. Additionally, the authors thank the China Institute of Water Resources and Hydropower Research for experimental support. Finally, the authors would like to express their sincere gratitude to all of those who have offered selfless help during the course of this research. All authors ([PERSON], [PERSON], [PERSON], [PERSON], [PERSON], [PERSON]) contributed to the research work.