Dependency on Runner Geometry for Reversible-Pump Turbine Characteristics in Turbine Mode of Operation

Abstract

Characteristics of a reversible-pump turbine have been measured with five different leading edge profiles in turbine mode. These profiles varied the inlet blade angle and the radius of curvature. Further geometry parameters have been investigated through numerical simulations. The pump turbine tested has much steeper flow-speed characteristics than a comparable Francis turbine. The most obvious geometry difference is the inlet part of the runner blades, where the blade angle for the pump turbine is much smaller than for the Francis turbine. Two different blade angles have been tested on a physical model and computational fluid dynamics (CFD) simulations have been performed on four different angles. Both methods show that a smaller blade angle gives less steep characteristics in turbine mode, whereas the measured s-shape in turbine brake- and turbine pumping mode gets more exaggerated. Long-radius leading edges result in less steep characteristics. The unstable pump turbine characteristics are in the literature shown to be a result of vortex formation in the runner and guide vane channels. A leading edge with longer curvature radius moves the formation of vortices towards higher speed of rotation.

Review on S-Shape Characteristics of Pump Turbine for Hydropower Generation

“…A comprehensive parametric research on the impact of runner leading edge of a pump-turbine on the performance curve was accomplished by. [1] in Identifying the complex flow patterns at the runner inlet on the S-shaped characteristics. [43] projected a start-up plan for hydraulic turbines prone to S-shaped characteristic, based on a gain scheduling technique from finite horizon predictive control.…”

“…Nevertheless, pump turbine design comes from the outcome of a cooperation amongst the conflicting targets such as performance of pump and turbine, regulatory capacity, efficiency and cavitation behavior. The design criteria, which are more focused on the behavior of the pumping function, such as the increase in the depth of the flow field at the depth of the flow field can result in the operation of the unstable region (called the S-shaped region) which doesn't have impact on Francis turbines functioning at the same conditions [1]. In view of the strong fluctuation of the torque caused by the occurrence of instability in the region, the RPT can be affected by a sudden change in the function (from turbine to pump and vice versa), along with substantial fluctuations of the head and flow rate through conceivable self-excited vibrations [2] otherwise water hammers emphasizing not the mechanical equipment alone but the entire power plant [3].…”

Parametric Design of an Ultrahigh-Head Pump-Turbine Runner Based on Multiobjective Optimization

“…The Reynolds stresses are modeled according to the turbulent viscosity hypothesis as 2 ( ) 3 [10,22,23,25]. In this study, RNG k ε − turbulence model was used for the closure of the RANS equations with the standard wall function method since it is economical and robust for predicting steady calculation with acceptable accuracy [25].…”

“…The profile of the runner can be modified by changing the design parameters on the basis of internal flow analysis [10,11]. However, this CFD flow analysis cannot directly propose a blade configuration with favorable flow pattern.…”

Prediction Method for the Complete Characteristic Curves of a Francis Pump-Turbine

“…When the pump-turbine is running stably in turbine mode, ignoring the flow loss at the runner and assuming that the flow distribution of the runner inlet or outlet is uniform, the flow through it can be calculated as follows [30][31][32]:…”