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.

Measurements have been performed on a reversible-pump turbine model installed in a closed loop conduit system. The characteristics of the unstable pump turbine in turbine mode show a hysteresis pattern. Hence the output of the system is dependent on the previous state of the flow and not only the input variables. The hysteresis pattern is a characteristic of the whole system, but is caused by the unstable pump turbine. The unstable part of the characteristics was measured by three different methods: 1) by transient sampling of data during the transition between operation modes, 2) by throttling valves that steepens the friction-loss curve, and 3) by switching the causality in the system such that the torque becomes an input parameter and the speed of rotation becomes an output parameter. In the valve throttling measurements a pressure dependency was seen for the characteristics at high nondimensional speeds. This was further investigated by additional measurements of the characteristics at three different pressure levels. A rigid-water-column stability analysis has been conducted. The classic H-Q criterion describes static stability for a pump turbine with constant speed of rotation. With the speed of rotation as a variable, there is a new static stability criterion in addition to the dynamic stability criterion.

This paper presents results from an experiment performed to obtain the dynamic characteristics of a reversible pump-turbine model. The characteristics were measured in an open loop system where the turbine initially was run on low rotational speed before the generator was disconnected allowing the turbine to go towards runaway. The measurements show that the turbine experience damped oscillations in pressure, speed and flow rate around runaway corresponding with presented stability criterion in published literature. Results from the experiment is reproduced by means of transient simulations. A one dimensional analytical turbine model for representation of the pump-turbine is used in the calculations. The simulations show that it is possible to reproduce the physics in the measurement by using a simple analytical model for the pump-turbine as long as the inertia of the water masses in the turbine are modeled correctly.

A full-scale Francis turbine has been experimentally investigated over its full range of operation to detect draft tube swirling flows and cavitation. The unit is of interest due to the presence of severe pressure fluctuations at part load and of advanced blade suction-side cavitation erosion. Moreover, the turbine has a particular combination of guide vanes (20) to runner blades (15) that makes it prone to significant rotor-stator interaction (RSI). For that, a complete measurement system of dynamic pressures, temperatures, vibrations, and acoustic emissions has been setup with the corresponding transducers mounted at selected sensitive locations. The experiments have comprised an efficiency measurement, a signal transmissibility evaluation, and the recording of the raw signals at high sampling rates. Signal processing methods for demodulation, peak power estimation, and cross correlation have also been applied. As a result, draft tube pressure fluctuations have been detected around the Rheingans frequency for low loads and at 4% of the rotating frequency for high loads. Moreover, maximum turbine guide bearing acoustic emissions have been measured at full load with amplitude modulations at both the guide vane passing frequency and the draft tube surge frequency.

The hump feature is one of the major instabilities in pump-turbines. When pump-turbines operate in the hump region, strong noise and serious fluctuations can be observed, which are harmful to their safe and stable operation and can even destroy the whole unit as well as water conveyance system. In this paper, a low specific speed (n_q = 36.1 min⁻¹) pump-turbine model was experimentally investigated. Firstly, the hump characteristic was obtained under 19 mm guide vane opening conditions. More interestingly, when the hump characteristic was measured in two directions (increasing and decreasing the discharge), characteristic hysteresis was found in the hump region. The analysis of performance characteristics reveals that the hump instability is the result of Euler momentum and hydraulic losses, and different Euler momentum and hydraulic losses in the two development processes lead to the hysteresis phenomenon. Then, 12 pressure sensors were mounted in the different parts of the pump-turbine model to obtain the time and frequency characteristics. The analysis of the corresponding fast Fourier transform confirms that the hump characteristic is related to low-frequency (0.04–0.15 times rotational frequency) vortices. The occurrence and cessation of vortices depend on the operating condition and measurement direction, which contribute to the hysteresis feature. Finally, the type of the low-frequency vortices was analyzed through the cross power spectrum.

The goal in the field of modeling of hydraulic transients is a comprehensive model for pipe networks that is computationally fast and accurate. The fastest models are the one-dimensional (1D) models that use instantaneous acceleration–based (IAB) properties, but unfortunately these models are not as accurate as the more demanding 1D convolution-based (CB) models or quasi two-dimensional models. Focusing on a single pipe, this paper investigates the fundamental behavior of the much more accurate 1D CB model to find two coefficients for use with the two-coefficient formulation of the much-used modified IAB (MIAB) model for complete closing of a downstream valve. Two coefficients are found based on the weighting function used in the CB model, and these coefficients vary along the pipe length. Simulations are compared with two experimental results from tests performed at University of Adelaide in Australia in 1995. The experimental results are for different initial Reynolds numbers of approximately 2,000 and ...