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ABSTRACTInclined overflow gates are widely used in open channels to meet different flow rate requirements by promptly adjusting their openings according to varied water levels. The characteristics of such gates are quite complex and need intensive study. To develop an effective and efficient numerical method for studying the hydrodynamic features of similar engineering structures with fluid structure interactions and free-surface flows, we propose a free-surface lattice Boltzmann-immersed boundary (FSLB-IB) coupling model, in which the free-surface flow is modeled by the lattice Boltzmann (LB) method and the moving boundaries are handled by the immersed boundary (IB) method. To solve the incompatibility issue arising from the coupling of the FSLB model and IB method, two treatments, namely the velocity correction in the empty cells for matching the IB speed with the local fluid velocity, and the iterative force-correction for enhancing accuracy, are introduced. The feasibility and accuracy of the proposed coupling scheme are first validated by two benchmark cases. Then the FSLB-IB scheme is applied to analyze the hydraulic characteristics of an inclined overflow gate in different working conditions. The good agreements between the simulated and empirical hydraulic parameters as well as the reasonable flow features show that the proposed coupling scheme is feasible for simulating practical hydraulic problems.

Variable speed operation has emerged as a key direction in the development of pumped storage technology. Maintaining pressure pulsation within the control range is particularly critical for ensuring operational safety of variable-speed pumped storage plants (VSPSPs). However, there is limited research on the relationship between pressure pulsation for pump-turbine and variable speed operation. This paper presents amplitude distribution diagrams of pressure pulsation, obtained from processing model test results of a real VSPSP. Different conditions of variable speed operation are simulated by a numerical model to analyze the influence of operating trajectory on pressure pulsation, and the intensity of pressure pulsation is quantitatively evaluated. According to the results, when the initial speed or speed command increases, the trajectory passes through more regions with high-amplitude pressure pulsation and gradually moves toward the S-shaped region, leading to pressure oscillations. When speed command reduces, maximum pressure pulsation at the volute inlet and in the draft tube can be reduced by 82.18% and 63.24% at most, and the evaluation score can be increased by 28.77%. The findings of this study can offer theoretical guidance for operating VSPSPs.

We demonstrate theoretically an analog of electromagnetically induced transparency (EIT) in the plasmonic metamaterial with the unit cell consisting of three parallel metallic rods. The electromagnetic mechanism for the EIT-like transmission is discussed based on our investigation of the localized surface plasmon resonances in three trirod configurations. We find that the transmission minima surrounding the transparency window on both sides correspond to two detuned magnetic resonances, which arise respectively from the antiphase plasmon couplings between a long rod and a short rod and between two short rods. A decrease of more than 10 times in the group velocity can be achieved for the trirod structure at the transparency window in the optical regime, and the EIT-like response can be well described by the theoretical model of two harmonic oscillators. This work not only reveals the EIT-like transmission in plasmonic metamaterial consisting of detuned magnetic “atoms,” but also provides further insight into the plasmons’ interactions, especially for metallic nanostructures comprising multiple metallic elements.

The ceiling-sloping tailrace tunnel is a new type of tailrace structure for underground hydropower stations and has been selected to replace the tailrace surge tanks in three large-scale hydropower plants in China. During the starting and load rejection conditions of turbine-generator units, the complex free surface-pressurized transient flow occurs in the tailrace tunnel. In this paper, a three-dimensional computational fluid dynamics research code with the volume of fluid (VOF)model is applied to simulate this special flow. After reviewing the ceiling-sloping tailrace tunnel structure and existing simulation methods, the mathematical models and numerical strategies are outlined. Then, the combined transient flow under a load rejection condition is simulated. Comparing with model test data, the flow patterns and pressure surge characteristics are analyzed intensively. The generation, development and breakup of the trapped large air bubbles in the interface region are also studied based on two-phase theory and the flow field results. It is shown that the flow is a special free surface-pressurized flow with a clear and regularly moving interface region, the interfacial large bubbles have no potential to generate large pressures harmful to the tunnel structure and the VOF model is a feasible and more advanced method to simulate this problem

The fluid-structure coupled simulation of the heart, though at its developing stage, has shown great prospect in heart function investigations and clinical applications. The purpose of this paper is to verify a commercial software based fluid-structure interaction scheme for the left ventricular filling. The scheme applies the finite volume method to discretize the arbitrary Lagrangian–Eulerian formulation of the Navier–Stokes equations for the fluid while using the nonlinear finite element method to model the structure. The coupling of the fluid and structure is implemented by combining the fluid and structure equations as a unified system and solving it simultaneously at every time step. The left ventricular filling flow in a three-dimensional ellipsoidal thin-wall model geometry of the human heart is simulated, based on a prescribed time-varying Young’s modulus. The coupling converges smoothly though the deformation is very large. The pressure–volume relation of the model ventricle, the spatial and temporal distributions of pressure, transient velocity vectors as well as vortex patterns are analyzed, and they agree qualitatively and quantitatively well with the existing data. This preliminary study has verified the feasibility of the scheme and shown the possibility to simulate the left ventricular flow in a more realistic way by adding a myocardial constitutive law into the model and using a more realistic heart geometry.