Although chute aerators have been investigated experimentally by many researchers, only a few studies have been conducted on the comprehensive air–water flow properties of the lower jet downstream chute aerators. In this study, after eliminating the upper aeration of the jet, a complete characterization was recorded and presented for the distributions of air concentration, air–water velocity, and bubble frequency. Based on these extensive tests, a comprehensive equation to compute the air concentration distributions of each zone was presented. The velocity distribution had a shape similar to that of shear air–water flows; however, the quantitative parameters differ in each zone. In the cavity zone, the position of the maximum air bubble frequency was largely within a region of relatively high air concentration and gradually approached an equal air concentration of 0.50. The location of the maximum air bubble frequency was approximately the same as that of the section maximum air concentration at a section in the impact zone, but lower than that in the equilibrium zone. Self-similar relationships between the air concentration and bubble frequency were proposed for each zone.

Under the influence of extreme weather conditions or other unfavorable factors, if a dam break occurs in a mountain river, it will cause a great number of casualties and property losses in the affected downstream areas. Usually, early warning of the affected areas downstream of the dam depends mainly on qualitative evaluation and cannot be quantitatively evaluated. Based on the authors’ calculation of floods for many years, this study presents a quantitative assessment method for flood risk. The Ertan Hydropower Station in Southwest China and the flood-affected areas were chosen as the object of this study. Based on field surveys, research literature data, and the authors’ calculations, the basic data of the Ertan Hydropower Station and the calculation results of the dam break were obtained, and 35 representative flood-affected areas were selected to study risk assessment and early warning. The fuzzy analytic hierarchy process (FAHP) was used to build a mathematical model for quantitative analysis. The population, flood arrival time, flood level, evacuation time, and local GDP (Gross Domestic Product) were selected as five typical evaluation factors. Finally, this study calculated and counted the risk level of 35 representative flood-affected areas, and the study results were applied to Quxue and Guanmaozhou Hydropower Station.

Spillway outlet design is a major issue in hydraulic engineering with high head and large discharge conditions. A new type of design for a streamwise-lateral spillway is proposed for ski-jump flow discharge and energy dissipation in hydraulic engineering. The water in the spillway outlet is constrained by three solid walls with an inclined floor, a horizontal floor on the bottom and a deflected side wall in the lateral direction. The water flow releases in a lateral direction into the plunge pool along the streamwise direction. It generates a free jet in the shape of “∩” in a limited area, causing the water to fully diffuse and stretch in the air simultaneously, and drop into the plunge pool to avoid excessive impact in the plunge pool. The formation mechanism for the flow pattern is analyzed, and the results show that the optimum inclination is an angle range of 30°~45° for a good performance of free ski-jump jet diffusion shape.

In this study, a new variable curvature bend called the maximum probability bend was applied to supercritical flows. Based on the maximum probability bend, the geometric and mechanical continuity of supercritical flow were studied, and the regulation of its superelevation, that is, the water surface elevation difference between both sides in every cross section, was analysed. The hydraulic characteristics of both the maximum probability bend and the traditional fixed curvature bend were experimentally investigated. It was found that the flow transitioned stably between straight and curve reaches in the maximum probability bend. Furthermore, the superelevation is reduced by a maximum of 65% compared with that in the traditional fixed curvature bend. Data comparison indicated that the proposed theory agreed well with the experimental results in terms of superelevation and the bend apex position. It was concluded that the maximum probability bend performed much better than the traditional fixed curve bend in supercritical flow control.

The flood propagation at a confluence of channels exhibits a unique routing pattern, while there are few studies on the routing of dam-break flow in confluent channels. In this study, we conducted physical experiments and a numerical simulation to investigate the influence of different confluence angles on the routing of a dam-break flood. Experiments were carried out in smooth, transparent, rectangular prismatic channels to study the dam-break flow under four different confluence angles. The flow velocity was measured using an image processing technique, and the surface flow field was effectively captured by synchronously recording the particle motion images. Based on the variation of the water level and flow discharge, as the confluence angle increased, the retardation and abatement effects on the flood increased. Specifically, the flood arrival time was delayed by approximately 0.91% to 21.18%, and the peak flood discharge was reduced by approximately 9.05% to 58.36%. Combined with the surface flow field at the confluence and in the downstream sections, as the confluence angle increased, the impact points at the confluence and in the downstream straight sections moved upward, and the impact range was reduced. Combined with the pressure variation pattern, the routing of dam-break flow in the confluent channels experienced a process of impact-reflection-return-attenuation.

In this study, we use a lattice Boltzmann method with a multi-relaxation-time model to simulate dam-break flooding in confluence channels with four confluence angles. Compared with physical experiment, the simulation proves reliable. We analyze the influence of the confluence angle on the propagation of dam-break flood. The stage hydrograph at the confluence area can be divided into four stages: before the wavefront reaches—rising rapidly—falling gradually—planarization with periodic fluctuation. The water depth of the measuring points in the confluence area is influenced by two factors: the confluence angle and the distance from the measuring point to the first impact point. The results demonstrate that the backwater effect of the confluence is enhanced at higher confluence angles. As the confluence angle increases, the first impact point moves upstream. Moreover, there is a strong backwater effect close to the first impact point, resulting in superelevation mainly occurring in the confluence area.