The energy-conversion stability of hydropower is critical to satisfy the growing demand for electricity. In low-head hydropower plants, a gravitational surface vortex is easily generated, which causes irregular shock vibrations that damage turbine performance and input-flow stability. The gravitational surface vortex is a complex fluid dynamic problem with high nonlinear features. Here, we thoroughly investigate its essential hydrodynamic properties, such as Ekman layer transport, heat/mass transfer, pressure pulsation, and vortex-induced vibration, and we note some significant scientific issues as well as future research directions and opportunities. Our findings show that the turbulent Ekman layer analytical solution and vortex multi-scale modeling technology, the working condition of the vortex across the scale heat/mass transfer mechanism, the high-precision measurement technology for high-speed turbulent vortexes, and the gas–liquid–solid three-phase vortex dynamics model are the main research directions. The vortex-induced vibration transition mechanism of particle flow in complex restricted pipelines, as well as the improvement of signal processing algorithms and a better design of anti-spin/vortex elimination devices, continue to draw attention. The relevant result can offer a helpful reference for fluid-induced vibration detection and provide a technical solution for hydropower energy conversion.

Multiphase vortices are widely present in the metallurgical pouring processes, chemical material extraction, hydroelectric power plant energy conversion, and other engineering fields. Its critical state detection is of great significance in improving product yield and resource utilization. However, the multiphase vortex is a complex dynamics problem with highly nonlinear features, and its fluid-induced vibration-generation mechanism faces significant challenges. A fluid-solid coupling-based modeling method is proposed to explore mass transfer process with the vorticity distribution and vibration-generation mechanism. A vibration-processing method is utilized to discuss the four flow-state transition features. A fluid-induced vibration experiment platform is established to verify the numerical results. It is found that the proposed modeling method can better reveal the vibration-evolution regularities of the fluid-solid coupling process. The flow field has a maximum value in the complex water–oil–gas coupled flow process, and induces a pressure pulsation phenomenon, and its frequency amplitude is much larger than that of the water phase and water–oil two-phase flow states. In the critical generation state, the increasing amplitude and nonlinear step structure of high-frequency bands (45 Hz~50 Hz) and random pulse components can be used for the online detection of multiphase-coupling states.