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.

Accurately predicting ski-jump flood discharge atomization is crucial for designing effective disaster-mitigation measures, particularly because low ambient pressure increases the risk of atomized protection in high-altitude regions. However, owing to the complex effects of low ambient pressure on strongly coupled atomized field sources, it is difficult to fully describe the comprehensive behaviour of such sources theoretically, which limits the further development of random splashing numerical models. In this paper, a refined random splashing numerical model characterized by low ambient pressure is developed based on experimental results and applied to high-altitude earth–rockfill dam projects. Compared with the reference ambient pressure condition ( P ₀ = 101.457 kPa), which corresponds to the same flood discharge flow, a decrease in ambient pressure by 0.1P ₀ leads to a maximum change rate not exceeding 10 m for the characteristic boundary of the 10 mm/h atomized rain intensity line at the QX Hydropower Station. This observation also applies to both the 40 mm/h and 10 mm/h atomized rain intensity lines at the RM Hydropower Station. For the two groups of flip bucket types designed for the RM Hydropower station, the loads associated with atomized protection are predominantly concentrated on the left bank. The maximum height of the 10 mm/h atomized rain intensity line affected by atomized rain ranges from 0.83 to 0.85 times the maximum dam height of 315 m. The distance between the farthest downstream boundary and the Spillway No. 3 outlet is between 666.80 and 692.40 metres. Since the flip bucket shape variations only slightly affect the atomization zone extent, further optimization is needed. The study can provide valuable methodological and decision-making support for safeguarding against existing and potential impacts within areas affected by flood discharge atomization from high-altitude hydropower stations.

Combined damage caused by cavitation and abrasion is a serious problem concerning hydraulic structures and machinery operating in hyper-concentrated sediment-laden rivers. Conceptualization of a model for simulation and assessment of the combined damage, therefore, becomes necessary. Experimental results demonstrate that sediments cast a strong influence on the combined damage caused by cavitation and abrasion. Sediments with size larger compared to a critical size tend to aggravate the combined damage, while sediments with size smaller compared to critical relieve the combined damage effect when compared against cavitation-only damage. Based on these results, a new model has been proposed and built in order to predict the combined damage and assess the range of sediments that relieve or aggravate the damage as sediments pass through the structure and machinery. The model represents an integral with damage as the integrand and sediments representing the domain of integration, and was built in three steps—the first step establishes a relationship between damage and sediments of a single size (SS model); the second step establishes a relationship between damage and sediments from an actual river (MS model); and the third step proposes a standard to assess the damaging effect on hydro machinery (CS model). Model parameters were verified using 74 cases of laboratory experiments. By comparing simulation results against experimental data, it has been inferred that the proposed model can be employed to study practical problems in a predictive manner and promote safe operation of reservoirs by predicting damage characteristics of river water.

The effect of sediment on the hydraulics of jet energy dissipation is an urgent issue for high dams built on sediment-laden rivers. Accordingly, flume experiments were conducted using a ski-jump type energy dissipator in flows of four sediment concentrations (0 kg/m³, 50 kg/m³, 150 kg/m³, and 250 kg/m³) to determine the effects on discharge, flow regime, and hydrodynamic pressure in a plunge pool. The results demonstrate that the effect of sediment on discharge is constant, regardless of sediment concentration, when compared to fresh water. The width of the nappe decreased with increasing concentrations of sediment. The length of the jet trajectory increased with upstream water head. The time-averaged pressure and fluctuation pressure both exhibited peaks, describing the impact of the jet on the bottom of the plunge pool. The maximum time-averaged pressure and maximum fluctuating pressure both noticeably increased with upstream water head and slightly increased with sediment concentration for a given flow condition. The results also demonstrated that the dominant frequency of fluctuation trends to lower values, and that both the fluctuating energy and vortex scale increase with increasing sediment concentrations due to increased viscosity. These findings can be used to improve energy dissipation in dams on sediment-laden rivers.

This study discusses the effects of geometrical parameters of flaring gate piers, such as contraction ratio, sidewall extension ratio and plunge angle, on the impinging pressure and flood atomization based on hydraulic model tests and atomization simulations. It is found that the impinging pressure decreases and the length of rainstorm increases with the increasing impact collision of aerated jets. Decreasing the plunge angle and increasing the extension length of sidewall for violent collision should be considered in the design stage and protection measures for rainstorms should be taken into account. Reducing the atomization hazard by collision avoidance could be selected in the operational phase on the premise of safety factor of plunge pool. A simplified formula is developed to predict the length of rainstorm as a function of the maximum impinging pressure, for use as a reference in the design and modification of similar projects.

The downstream nappe wind caused by flood discharge has a great influence on the rainfall distribution, the operational safety of dams, and their surrounding ecological environments. A physical experiment was conducted to measure the spatial distribution of the downstream nappe wind and the splash for a continuous bucket (CB) and a tongue-shaped bucket (TB) for five bucket angles (40°, 45°, 50°, 55°, and 60°). The experimental results demonstrate that the trajectory width and height of the nappe increase as the angles increase, but the effect on the length is converse. The wind velocity and splash weight of the two buckets decrease along the flowing direction. In the lateral direction, the wind velocity and splash weight for the CB decrease as y increases, but the wind velocity of the TB trends to humplike; its splash weight decreases near the axis of the bucket, and is stable in the other region. In the vertical direction, the velocity for the CB increases and then decreases as z increases, but that for the TB decreases monotonously. The velocity of the wind and weight of the splash for the CB decreases with the increasing angles, but those of the TB peak at 45°. The findings are useful for the more accurate prediction of rainfall.