Understanding the formation mechanism of S-shaped characteristics (SSCs) and relationship between flow structures runaway instability (RI) is prerequisite for optimizing runner design to promote operational reliability flexibility. In this study, a new turbine equation derived reveal prime cause SSCs, influence geometric parameters on SSCs analyzed. Moreover, patterns in three model turbines different specific-speeds are simulated by unsteady Computational fluid dynamics (CFD), correlation...

The pressure fluctuations and runner loads on a pump-turbine during runaway process are very violent the corresponding flow evolution is complicated. To study these phenomena their correlations in depth, processes of model at four guide vane openings (GVOs) were simulated by three-dimensional computational fluid dynamics (3D-CFD). results show that structures around inlet have regular development transition patterns—the reverse occurs when trajectory moves to turbine-brake region main...

During transients, hydroturbines may demonstrate some dynamic characteristics that differ from the corresponding static in steady operating conditions. To study of a pump-turbine, we simulated runaway transients model pumped-storage plant by coupling one-dimensional (1D) water conveyance system and three-dimensional (3D) pump-turbine. The results show trajectories form loops S-shaped region unit discharge torque charts not following characteristics. Theoretical analysis flow patterns...

Rotating stall may occur at part load flow of a pump-turbine in pump mode. Unstable structures developing under condition can lead to sudden drop efficiency, high dynamic and even cavitation. CFD simulations on model mode were carried out reveal the onset developed mechanisms these unstable phenomena load. The simulation results energy-discharge efficiency characteristics are good agreement with those obtained by experiments. more deviate from design conditions decreasing rate, separations...

To fully understand the evolution of flow structures and pressure fluctuations in S-shaped region pump-turbines, three dimensional (3D) numerical simulations were carried out for a model pump-turbine at four different guide-vane openings (GVOs). We found that special backflow vortex (BFVSs) form around runner inlet. The location shifts from hub side to shroud then midspan, as operating point moves best efficiency zero discharge along characteristic curve. At large GVO, if is relatively...

Frequent working condition conversions in pumped-storage power stations often induce stability problems, especially when the operating point enters S-shaped region, during which flow transitions and pressure fluctuations are serious. The pump-turbines with different specific speed values show characteristics, but their differences features still not clear. In this study, four were selected to simulate runaway processes from turbine modes. similarities of patterns analyzed. For similarities,...

This paper reports the preliminary progress in CFD simulation of reverse water-hammer induced by collapse a draft-tube cavity model pump-turbine during runaway process. Firstly, Fluent customized 1D-3D coupling for hydraulic transients and Schnerr & Sauer cavitation development are introduced. Then, methods validated simulating benchmark long pipe caused valve instant closure. The simulated head history at agrees well with measured data literature. After that, more complicated pump-turbine,...

The runaway oscillation process of the pump-turbine in a high head pumped-storage power plant is usually unstable. root cause its instability still unclear. In this paper, internal mechanism and improvement method were studied depth. First, flow characteristics model during at four guide-vane openings (GVOs) investigated by 3D transient numerical simulations. Then, energy dissipation different types backflow vortex structures (BFVSs) occurring runner inlet their impacts on stability entropy...

The most detrimental pressure pulsations in high-head pump-turbines is caused by the rotor-stator interaction (RSI) between guide vanes and runner blades. When pump-turbine operates S-shaped region of characteristic curves, deteriorative flow structures may significantly strengthen RSI, causing larger stronger vibration with an increased risk mechanical failure. CFD simulations were carried out to analyze impacts evolution on a model pump-turbine. results show that reverse vortex (RFVS) at...

The runaway process in a model pumped-storage system was simulated for analyzing the dynamic characteristics of pump-turbine. simulation adopted by coupling 1D (One Dimensional) pipeline MOC (Method Characteristics) equations with 3D (Three pump-turbine CFD (Computational Fluid Dynamics) model, which water hammer wave zone defined giving pressure dependent density. We found from results that performances do not coincide static operating points, especially S-shaped region, where trajectories...

The transient behaviour of the pump-turbine in load rejection is very complex, and slight changes runner blade shape may have great influence on it. To understand underlying flow mechanisms, processes two model pump-turbines with same specific-speed but different inlet were investigated by a three-dimensional numerical simulation method. results show that lean angle leading edge impacts evolution backflows at inlet. first emerge shroud side for negative angle, hub no angle. However, make...

The relations between the runaway stability characteristics and flow patterns inside runner of pump-turbine are supposed to be close should studied. processes a model at four guide-vane openings (GVOs) were simulated by three-dimensional computational fluid dynamics. results show that for different GVOs. For small GVOs, turbine characteristic trajectory undergoes damped oscillations; however, large settles into an un-damping oscillation. evolution features reverse vortex structures (RFVS)...

The collision of guide vanes with runner a pump-turbine during transient processes is rarely seen in pumped-storage power stations, but the consequence serous when happens. To investigate reason case such an accident, we analyse evolution rules vane moment runaway process after pump trip prototype system by using 1D-3D method. First histories macro parameters as flow rate, rotational speed and trajectory working condition point are given. Secondly, difference under different conditions...

Three-dimensional numerical simulations were carried out to investigate the transient behaviours of a model pump-turbine during load rejection processes. The influences guide-vane closing schemes on evolutions flow patterns, pressure fluctuations and runner forces investigated. results show that when trajectory operating point moves through region with backflows occurring at hub side inlet, in vane-less space unstable radial force become severe, which are duo enhanced momentum exchange...

Simulating shallow water flows in large scale river-lake systems is important but challenging because huge computer resources and time are needed. This paper aimed to propose a simple efficient 1D–2D coupled model for simulating these flows. The newly developed lattice Boltzmann (LB) method was adopted simulate 1D 2D flows, of its easy implementation, intrinsic parallelism, high accuracy. coupling strategy the interfaces implemented at mesoscopic level, which unknown distribution functions...