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The operation conditions of the pump-turbine are changed frequently and are worse than the conventional turbine. The operation stability of the pump-turbine is more focused with the incremental unit capacity and the pump-turbine runner diameter. The research of the measurement method for the dynamic stress and the pressure of the model pump-turbine splitter runner blades is performed to evaluate the stress and pressure distribution under the various operation conditions, it is optimized for the turbine mechanical and hydraulic computation, the operation references are provided for the prototype pump-turbine also. In this paper, the measurement positions of the blades are determined based on the hydraulic CFD and mechanical computation, the measurement method of dynamic stress and pressure of model pump turbine-runner splitter blades is studied.

When the pump turbine does variable speed operation, it can improve the operation efficiency in the turbine mode, and it can improve the automatic frequency adjustment efficiency in the pump mode. However, the hydraulic thrust will also change when the speed changes, and the magnitude of the hydraulic thrust is crucial for the safe and stable operation of the unit. The work of this paper is to analyze the changes of the axial hydraulic force and radial force with the change of the speed by numerical simulation method. It is found that the fluctuation of axial hydraulic thrust can reach about 34 t at 398.57rpm speed, 37 t at 412.16rpm speed and 21 t at 428.6rpm speed. the fluctuation of radial force can reach about 13.78 t, 14.4 t and 12.4 t. The purpose of this paper is to use the simulation results to understand the hydraulic thrust characteristics and ensure the stability of the unit to select the appropriate speed range, provide the basis for stable operation of the unit under design conditions.

The size of the runner crown gap is one of the factors affecting the volume loss of the pump turbine, and the unreasonable gap thickness is unfavourable to the unit operation. By establishing a three-dimensional full-channel fluid domain model of a high-head pump turbine, and using the computational fluid dynamics (CFD) method to perform numerical calculations on models with different crown gap thicknesses, the effects of axial water thrust on runners with different upper crown gap thicknesses are clarified. The results of simulation indicates that the resultant force of axial water thrust on the runner is vertically upward under different gap thicknesses, which is far less than the weight of the whole rotating part. The axial water thrust is very sensitive to the change of the seal gap value, the greater the seal gap value, the greater the axial water thrust on the unit, and the axial water thrust begins to decrease after increasing to a certain value. The research results are referable for the study of the gap flow characteristics and the crown gap design.

The power-trip of the pump under certain conditions leads to the runaway of the unit, causing dangerous transitional process in pumped storage power stations. This process is characterized by transient hydraulic features like flow separation and vortex structures, which increase hydraulic losses significantly and severely impact unit efficiency and stability. This paper aims to elucidate the mechanism of energy loss due to unstable flow during pump turbine runaway. It focuses on a high-head model pump turbine, examining the transient flow process from pump conditions to runaway conditions. It conducts quantitative analysis of energy loss using entropy production theory, besides, further clarifies the location and causes of hydraulic losses by integrating with internal flow analysis. The results show that a significant high-entropy production zone is captured in the pump braking condition, indicating extremely chaotic internal flow in this area during the runaway transition process. Additionally, throughout the transition process, turbulent entropy production initially increases, then decreases. Turbulent entropy production accounts for more than 80% of total entropy production, indicating that turbulent entropy production dominates throughout the entire transition process. The energy of the water is primarily dissipated within the runner during the runaway process. The maximum proportion is 87%, which is in the pump braking condition. Correlation analysis between flow and hydraulic losses reveals that vortex structure induced by flow separation under off-design conditions is the primary contributor to increased hydraulic losses.

The pumped-storage power station is an efficient stability regulator of the power grid. However, due to the instability of the pump-turbine in the S-shaped characteristic region, rotational speed fluctuation is easy to occur in the speed no-load condition, making synchronization with and connection to the grid difficult. To investigate the key factors of these difficult grid connections, the start-up processes of a practical pump-turbine under the lowest head condition were simulated by using the three-dimensional CFD method, in which the governor regulating equations with different regulating parameters were integrated successfully. The results show that the working points oscillate with the fluctuations of rotational speed, discharge, and torque, and different regulating parameters have a significant influence on the dynamic histories. In addition, the internal flow patterns, especially the backflows at the runner inlet, keep apparent values at the middle span (0.5 span) but have regular transitions near the shroud side (0.7–0.8 span). The faster the guide vanes adjust, the faster the backflows change, and the larger the macro parameters fluctuate. Overall, the instability of the start-up is the result of the periodical evolutions of backflows at the runner inlet, because the trend and period of the radial velocities at different inlet span locations are consistent with those of the discharge.

A reversible pump turbine is a large-scale commercial energy storage device that serves as the core component of a pumped storage power station. Under pump operating conditions, the reversible pump turbine often exhibits hump characteristics on the head–discharge performance curve, leading to operational instability and limiting both regulation performance and safety. However, the mechanism underlying flow instability in the hump region is not adequately understood. Existing analysis methods are limited in scope, and they struggle to identify key flow structures accurately in application. In this study, large eddy simulation (LES) is used to investigate unsteady flow characteristics under typical hump conditions. Proper orthogonal decomposition (POD) and dynamic mode decomposition (DMD) methods are applied to a transient flow field to extract dominant modal structures and analyze their dynamic behaviors. The results show that rotating stalls in the guide vane and runner regions are the primary factors creating hump characteristics. Both the POD and DMD methods effectively capture major vortex structures and their changes, demonstrating their suitability for analyzing complex flow dynamics. These findings provide theoretical insight into the flow instability mechanism in the hump region and offer guidance for improving the operational performance of pump turbines.

For the high head pump turbine, the unit instability during its operation mainly dues to the hydraulic vibration inside the machinery, which will cause the mechanical fatigue failure under certain circumstances. In this paper, the flow pattern and the runner axial water thrust in turbine model under partial load were analyzed by numerical simulation. The internal flow field instability and vortex load characteristics of the runner were analyzed to obtain the reasons for the different axial water thrust characteristics of the runner under two different loads. The results showed that due to the reduction of the guide vane opening, the flow rate is smaller at 50% load, and the free flow vortex structure on the high-pressure side of the runner blade inlet strengthens the impact of the water flow on the runner. Moreover, when the pressure difference between the runner blades decreases and the axial water thrust of the blades decreases, the total axial water thrust of the runner decreases and fluctuates frequently with time.

The hump formation mechanism has not been fully understood so far, mainly because of two difficulties in analysis. The first one is how to find the most important external characteristic factor inducing humps, and the other is how to avoid too many assumptions when analysing the change in the runner's capacity for work (the direct use of Euler's formula makes too many assumptions). This paper proposes a new method based on the second derivative of the external characteristics to identify the most critical factor inducing humps quantitatively. The runner blades' capacity for work is calculated and shown as a cloud diagram using as few assumptions as possible to help understand the actual relationship between flow fields and humps. Additionally, the importance of stall in affecting the runner's capacity for work is analysed and explained. Thus, the double hump formation mechanism in pump-turbines has finally been understood.

The dynamic characteristics of running away pump turbines (PTs) with a large head variable amplitude have not been understood thus far, primarily because of two difficulties in simulation and analysis. The first is how to provide accurate time-varying boundary conditions for transient simulation of the turbine runaway process (TRP). The other is how to determine the specific appearance time of each frequency component of the complex pressure fluctuations. This study presented a one- and three-dimensional (1D-3D) coupled approach considering waterway dynamics to provide accurate unsteady boundary conditions for the transient flow simulation of a PT with a large head variable amplitude. The short-time Fourier transformation (STFT) approach was adopted to analyse the time-frequency characteristics of the transient pressures and impeller forces. The study found that the fluctuations of pressures and impeller forces during the TRP of the PT with a large head variable amplitude contained two exclusive fluctuation frequency components. The former was approximately three times the rated rotational frequency of the impeller. The later was a series of integer fold transient rotational frequencies of the impeller, which was irrelevant to the rotor-stator interactions. The findings have important value for controlling the pressure fluctuations during the TRP of PTs.

In the last few years, the pumped storage power station grows vigorously. As a result, the higher demand have been put forward in relevant technical fields. This article mainly discusses the model test research of medium-low specific speed Francis pump-turbine. Furthermore, the pump-turbine model test method of performance, cavitation, pressure pulsation, complex characteristics, and the rest auxiliary test is expounded and studied, with a view to optimizing pump-turbine model test method and further improving test rate. It can provide the favorable condition for the pump-turbine unit design and power station continuously operation.