Runner Lifting-Up during Load Rejection Transients of a Kaplan Turbine: Flow Mechanism and Solution

“…It was found that by using any linear closing rule of the guide vane, the upward axial water force on the runner was larger than the weight of rotating parts that started before the guide vanes were closed, putting the hydropower station in a risky situation. It was the suction effect that caused the imbalance, induced by the high rotational speed runner that propels water downstream with a low discharge [31]. Another interesting study was developed by [32], showing a sensitivity analysis of the hydropower system parameters to the rotation speed and discharge.…”

Section: Dynamic Effects In Hydropower Systemsmentioning

confidence: 99%

Mathematic Modelling of a Reversible Hydropower System: Dynamic Effects in Turbine Mode

Ramos

Coronado-Hernández

Morgado

et al. 2023

Water

View full text Add to dashboard Cite

Over the past few years, there has been significant interest in the importance of reversible hydro-pumping systems due to their favorable flexibility and economic and environmental characteristics. When designing reversible lines, it is crucial to consider dynamic effects and corresponding extreme pressures that may occur during normal and emergency operating scenarios. This research describes essentially the turbine operation, although various boundary elements are mathematically formulated and presented to provide an understanding of the system complexity. Different numerical approaches are presented, based on the 1D method of characteristics (MOC) for the long hydraulic circuit, the dynamic turbine runner simulation technique for the behavior of the power station in turbine mode and the interaction with the fluid in the penstock, and a CFD model (2D and 3D) to analyze the flow behavior crossing the runner through the velocity fields and pressure contours. Additionally, the simulation results have been validated by experimental tests on different setups characterized by long conveyance systems, consisting of a small scale of pumps as turbines (at IST laboratory) and classical reaction turbines (at LNEC laboratory). Mathematical models, together with an intensive campaign of experiments, allow for the estimation of dynamic effects related to the extreme transient pressures, the fluid-structure interaction with rotational speed variation, and the change in the flow. In some cases, the runaway conditions can cause an overspeed of 2–2.5 of the rated rotational speed (NR) and an overpressure of 40–65% of the rated head (HR), showing significant impacts on the pressure wave propagation along the entire hydraulic circuit. Sensitivity analyses based on systematic numerical simulations of PATs (radial and axial types) and reaction turbines (Francis and Kaplan types) and comparisons with experiments are discussed. These evaluations demonstrate that the full-load rejection scenario can be dangerous for turbomachinery with low specific-speed (ns) values, in particular when associated with long penstocks and fast guide vane (or control valve) closing maneuver.

show abstract

“…Among them, the Kaplan turbine has been widely used because of its large flow rate, easier maintenance, and high efficiency. [1][2][3] As an important member of hydraulic machinery, it is mainly composed of rotating components (runner) and stationary components (spiral casing, stay vanes, draft tube, etc.). To avoid friction, tip clearance (Figure 1) between the runner blade tip and shroud is existed.…”

Section: Introductionmentioning

confidence: 99%

Flow behaviors in a Kaplan turbine runner with different tip clearances

Qian¹,

Zhang²,

Wang³

et al. 2021

Advances in Mechanical Engineering

View full text Add to dashboard Cite

Tip clearance between the runner blade tip and shroud in a Kaplan turbine is inevitable, and the tip leakage flow (TLF) and tip leakage vortex (TLV) induced by the tip clearance have a considerable effect on the flow behaviors. To reveal the effect of the tip clearance on the flow characteristics, based on the Reynolds time-averaged Navier-Stokes (N-S) equation and the shear stress transfer (SST) k-ω turbulence model, the three-dimensional turbulence flow in a Kaplan turbine is simulated using ANSYS CFX. Meanwhile, the flow laws in the tip clearance are emphatically analyzed and summarized. Results show with the increase of the tip clearance, the negative pressure region in the blade suction side (SS) middle, the SS near the blade tip and the blade tip becomes more and more obvious. In the meantime, the flow behaviors on the blade pressure side (PS) are relatively stable, and the flow separation on the SS near blade tip merges. The larger the tip clearance is, the more obvious the flow separation phenomenon displays. In addition, the TLV is a spatial three-dimensional spiral structure formed by the entrainment effect of the TLF and main flow, and as the tip clearance increases, the TLV becomes more obvious.

show abstract

Runner Lifting-Up during Load Rejection Transients of a Kaplan Turbine: Flow Mechanism and Solution

Cited by 14 publications

References 11 publications

On the criteria of large cavitation bubbles in a tube during a transient process

On the criteria of large cavitation bubbles in a tube during a transient process

Mathematic Modelling of a Reversible Hydropower System: Dynamic Effects in Turbine Mode

Flow behaviors in a Kaplan turbine runner with different tip clearances

Contact Info

Product

Resources

About