Check dams are widely located in the Loess Plateau area of western China. Their siltation elevation can exceed the design value after long-term running. The excess sediment spreads into the spillway, and then accumulates in front of the overflow weir, leading to the normal flood discharge. This study aims to clarify the influence of siltation thickness on the hydraulic characteristics of the broad-crested weir of check dams. The spillway of a typical check dam was also selected as the research object. The physical model test was finally carried out to analyze the flow pattern, water surface profile, velocity distribution, and discharge coefficient of overflow weir under different siltation heights. The test results were as follows: the upstream water surface of the broad crested weir was straight and flat under the condition of free flow. Then, the water level was dropped near the weir wall and gradually flattened just above the weir crest. Finally, the flow was fallen from the weir to the downstream channel. Sedimentation in front of the weir was reduced the degree of backwater, and thus the water depth dropped significantly. The overall water surface basically remained the same as that without sediment, and then gradually developed towards the open channel flow, with the increase of siltation thickness. More outstanding behavior was also found under small flow or low hydraulic head. The influence of siltation on the weir flow was further quantified using water surface profile. Therefore, the slight decrease was observed on the water surface line in front of and above the weir crest under different cases with the increase of sedimentation height, compared with the water depth along the weir. The water depth in the area behind the weir was depended mainly on the downstream channel, indicating no influence from the siltation height. Furthermore, there was an increase in the flow velocity in front of and behind the weir increases, where the reduced water level indicated the reduction of the cross-section area. Consequently, the rising siltation elevation increased the overflow capacity. It infers that the existing calculation formula cannot be applied for the calculation of spillway design in the check dams with the high siltation height. Thus, it is necessary to quantify the impact of siltation to calculate the discharge coefficient. The test data was substituted into the weir flow formula to deduce the test value of discharge coefficient under various working conditions. The discharge coefficient of the broad crested weir increased with the increase of hydraulic head using the general law of hydraulics. The siltation height shared a great influence on the weir flow coefficient under the same flow condition. Anyway, the discharge coefficient increased gradually with the increase of siltation height, indicating the enhanced overflow capacity of the broad crested weir. Therefore, the fitting empirical formula of discharge coefficient was obtained to introduce the relative siltation height α (Ratio of siltation height to weir height). The average relative error between the calculated and the measured values was 2.7%, fully meeting the accuracy requirements. The new formula can be applied to calculate the discharge coefficient. These findings can provide a strong reference for the check dams reinforcement.

Critical energy efficiency is often required in the fluid-structure interaction with the moving boundaries—such as hydraulic machinery, turbomachinery, and plunge pools. However, the previous research has focused primarily on the flow field identification. This work aims to specifically target the underexplored link between turbulent structures and energy dissipation. A systematic investigation was made on the energy consumption characteristics of the fully-developed slot flow under high Reynolds number (Re) conditions. Physical experimentation and theoretical analysis were employed for the hydrodynamic similarity and measurement accuracy. A scaled model consisted of an organic glass plate (2000 mm × 50 mm × 30 mm) translating uniformly within a 9 m long rectangular acrylic pipe (cross-section: 50 mm × 50 mm) at four controlled speeds (0.1, 0.2, 0.3, and 0.4 m/s). The flow regime was maintained at Re = 15000-22176 (all turbulent) with a fixed slot ratio (Ψ = 0.4). While Particle Image Velocimetry (PIV) was captured the instantaneous velocity fields, and high-speed cameras were used to track the plate kinematics. Furthermore, water temperature was stabilized at 27-28 °C for the viscosity consistency during experiments. The energy dissipation was obtained to quantify the turbulent kinetic energy, vorticity distributions, and viscous energy losses. At the same time, the energy loss from the moving boundary was analyzed to evaluate boundary effects using the velocity ratio (K=v_c/v_a, where va was the average slot flow velocity). Energy-saving efficiency (η = v_c/Q_d, with Q_d as energy loss per unit area and distance) was also introduced for quantitative evaluation. The results revealed that: 1) Turbulent kinetic energy near the moving plate boundary consistently exceeded the levels near static pipe walls, indicating the dominant role of boundary motion in energy transfer. The intensity of turbulent kinetic energy increased significantly by 80.6%-119.9%, as both Reynolds number and plate velocity rose. Boundary motion outweighed Reynolds number near localized high-shear regions. 2) Vorticity analysis demonstrated that the distribution exhibited symmetrically opposite values (ranging from -10 to 10 s⁻¹) around the pipe’s longitudinal central axis. Critically, the large-scale vortices near the pipe center (occupying 43%-66% of the slot area) caused the minimal energy loss, due to the weaker rotational intensity, whereas the small-scale vortices near the walls (12%-20% of the area) were induced substantial energy loss as a direct consequence of intense, localized rotation and momentum exchange. In energy dissipation dynamics, the energy loss from the moving boundary first decreased and then increased with the velocity ratio K, reaching the minimum when K=1.0. The wall shear stress was minimized, when the plate and flow velocities were nearly equal, effectively reducing viscous drag. 3) Reynolds number increments amplified the energy loss to thin the viscous sublayer, consequently increasing near-wall velocity gradients. Importantly, the quantitative assessment of efficiency revealed that the maximum wall energy-saving efficiency η, 1.72, occurred at Re=15 000, v_c=0.3 m, indicating a 43.33% improvement over the suboptimal condition (Re=15000, v_c=0.4 m/s, η=1.2) with an optimum for operational parameters. The energy consumption of slot flow with moving boundaries was determined with the relationships between turbulent kinetic energy, vorticity distribution, and energy loss. The energy-saving efficiency and identification of the optimal velocity ratio (K=1.0) can provide a practical reference to optimize the high-Reynolds-number fluid-structure interaction, particularly in the operation of hydraulic machinery and water conservancy structures. These insights ultimately facilitate the energy efficiency and operational stability using target control of near-wall turbulence and vortex-induced dissipation.

Step spillways have been used in the construction of small and medium-sized reservoirs, particularly with the concrete dam construction. The steps have been widely applied on the smooth spillway to increase the gas doping for energy dissipation through the violent turbulence of the water body. In this study, a combination of energy dissipating piers and steps was proposed to further improve the energy dissipation of the spillway, and then reduce the negative pressure on the step surface. The trapezoidal energy-dissipating piers were arranged at the convex corners of the steps. The model test and numerical simulation were used to investigate the flow pattern, flow velocity, pressure, and energy dissipation rate of the combined step energy dissipator under single-row and single-row staggered arrangement. The hydraulic characteristics were compared with the traditional step energy dissipator. The results show that the flow pattern of the combined step dissipator with the trapezoidal energy dissipation pier was basically the same as the traditional at the different relative critical water depths. The energy dissipation pier was arranged at the convex corner of the step, compared with the traditional one. The energy dissipation pier shared a provocative effect on the water flow in the transitional flow state, in order to enhance the energy dissipation. The pattern of the small bottom and large surface layer was found in the distribution of water flow velocity in the step cross-section of the trapezoidal energy dissipation pier combination. The range of flow velocity was expanded by about 2.4-3.1 times, compared with the traditional. In the position close to the step water surface, the water flow velocity of body type Ⅰ, and Ⅱ step energy dissipation were reduced by about 3.6% and 5.2%, respectively, compared with the traditional. The water flow was reduced on the step energy dissipation worker of the damage of the scouring. The negative pressure range of trapezoidal energy dissipation pier combination of step energy dissipation worker was reduced by 60% to 70%, of which the body type Ⅱ step energy dissipation worker produced the smallest value of the negative pressure, compared with the traditional. The negative pressure value of the body type Ⅱ step energy dissipator was the smallest, which was 42% less than that of the traditional. The cavitation damage was effectively reduced on the vertical surface of the step. The energy dissipation rate of the combined step energy dissipator decreased less than before with the relative critical water depth increasing from 0.714 to 1.486. The energy dissipation rate was still 70% or more under the condition of larger relative water depth. A better characteristic was achieved in the energy dissipation. The findings can also provide some references for practical engineering.