Hydrodynamic mechanism analysis of the pump hump district for a pump-turbine

Purpose Numerically analyzed the flow characteristic and explored the hydrodynamic mechanism of the pump mode hump district formation of a Francis pump-turbine. Design/methodology/approach Numerical simulations were conducted of the entire pump-turbine flow passage under different discharge conditions by adopting the SST-CC turbulence model. The internal flow at hump district has been explained in detail combined with the model test in this paper. The unsteady flow and pressure fluctuation characteristics are analysed under five different discharge conditions in the hump and nearby region. The reason of the hump district formation is explored combined with the flow components hydraulic loss. Findings The large hydraulic loss, high relative peak-to-peak amplitudes and low dominant frequencies are on account of the disorganized internal flow condition. The formation of the hump district is concerned with the large hydraulic loss inside the draft tube, runner and guide vanes as there occurs secondary flow, backflow even vortex in the hump district. In addition, the low dominant frequencies at recording points inside the flow passage are always accompanied with the change of flow patterns and the spreading of the pressure fluctuations. Originality/value The analysis method of each flow components hydraulic loss combined with internal flow structure is adopted to explore the mechanism of pump mode hump characteristic. The flow characteristic and pressure pulse characteristics all correspond to the flow components hydraulic loss.

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Analysis of the internal flow behavior on S-shaped region of a Francis pump turbine on turbine mode

Engineering Computations ◽

10.1108/ec-04-2015-0084 ◽

2016 ◽

Vol 33 (2) ◽

Cited By ~ 7

Author(s):

Yexiang Xiao ◽

Wei Zhu ◽

Zhengwei Wang ◽

jin zhang ◽

Chongji Zeng ◽

...

Keyword(s):

Design Methodology ◽

Flow Characteristic ◽

Stokes Equations ◽

Flow Behavior ◽

Internal Flow ◽

Optimal Operation ◽

Operating Conditions ◽

Unit Discharge ◽

Pump Turbine ◽

Runner Blade

Purpose Numerically analyzed the flow characteristic and explored the hydrodynamic mechanism of the S-shaped region formation of a Francis pump-turbine. Design/methodology/approach Three-dimensional steady and unsteady simulations were performed for a number of operating conditions at the optimal guide vanes opening. The steady Reynolds averaged Navier-Stokes equations with the SST turbulence model were solved to model the internal flow within the entire flow passage. The predicted discharge-speed curve agrees well with the model test at generating mode. This paper compared the hydrodynamic characteristics of for off-design cases in S-shaped region with the optimal operating case, and more analysis focuses particularly on very low positive and negative discharge cases with the same unit speed. Findings At runaway case towards smaller discharge, the relative circumferential velocity becomes stronger in the vaneless, which generates the “water ring” and blocks the flow between guide vane and runner. The runner inlet attack angle becomes larger, and the runner blade passages nearly filled with flow separation and vortexes. The deterioration of runner blade flow leads to the dramatic decrease of runner torque, which tends to reduce the runner rotation speed. In this situation, the internal flow can’t maintain the larger rotating speed at very low positive discharge cases, so the unit discharge-speed curves bend to S-shaped near runaway case. Originality/value The analysis method of four off-design cases on S-shaped region with the comparison of optimal operation case and the calculated attack angles are adopted to explore the mechanism of S characteristic. The flow characteristic and quantitative analysis all explain the bending of the unit discharge-speed curves.

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Performance characteristics and internal flow patterns in a reverse-running pump–turbine

Proceedings of the Institution of Mechanical Engineers Part C Journal of Mechanical Engineering Science ◽

10.1177/0954406211416304 ◽

2011 ◽

Vol 226 (3) ◽

pp. 695-708 ◽

Cited By ~ 12

Author(s):

R Barrio ◽

J Fernández ◽

E Blanco ◽

J Parrondo ◽

A Marcos

Keyword(s):

Stokes Equations ◽

Internal Flow ◽

Flow Patterns ◽

Performance Characteristics ◽

Centrifugal Pumps ◽

Pump Mode ◽

Modes Of Operation ◽

Pump Turbine ◽

Reverse Mode ◽

Numerical Predictions

Vaneless centrifugal pumps are reversible turbomachines that can operate also as centripetal turbines in low and very low-head power plants. However, the general performance in reverse mode is difficult to predict since the internal flow patterns are different from pump mode and the performance characteristics are not usually provided by manufacturers. This article presents numerical and experimental investigations on the operation of a reverse-running pump–turbine. The numerical calculations were carried out by solving the full unsteady Reynolds-averaged Navier–Stokes equations with the commercial code Fluent for several flowrates between 20 per cent and 160 per cent of rated conditions and both modes of operation. A complementary series of experimental measurements were performed in a test rig in order to obtain the general characteristics of the machine in pump and turbine modes, with the purpose of validating the numerical predictions. Once validated, the numerical model was used to investigate the flow patterns at some significant locations by means of pressure and velocity contours, and also by vector maps. Additionally, the model allowed the estimation of the steady load on the impeller as a function of flowrate in both modes of operation. It was concluded that, while the radial load in reverse mode is three times smaller than in pump mode, the axial load can be up to 1.6 times larger.

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Flow characteristics prediction in pump mode of a pump turbine using large eddy simulation

Proceedings of the Institution of Mechanical Engineers Part E Journal of Process Mechanical Engineering ◽

10.1177/0954408916651664 ◽

2016 ◽

Vol 231 (5) ◽

pp. 961-977 ◽

Cited By ~ 16

Author(s):

De-You Li ◽

Lei Han ◽

Hong-Jie Wang ◽

Ru-Zhi Gong ◽

Xian-Zhu Wei ◽

...

Keyword(s):

Large Eddy Simulation ◽

Flow Characteristics ◽

Internal Flow ◽

Pump Mode ◽

Pump Turbine ◽

Recirculation Flow ◽

Eddy Simulation ◽

Eddy Viscosity Model ◽

Large Eddy ◽

Operating Points

To obtain more accurate flow characteristics of pump turbines, the method of large eddy simulation with wall-adapting local eddy viscosity model is applied in simulating several operating points in the pump mode. Firstly, based on the experimental validation, the method of large eddy simulation could better predict the external performance and internal flow characteristics in a pump turbine in the pump mode compared with the method of Reynolds-averaged Navier–Stokes with two-equation turbulence model shear stress transport k–ω. Then, flow characteristics under 1.00 QBEP (best efficiency point), 0.91 QBEP, 0.88 QBEP, and 0.85 QBEP operating points are investigated to find out the causes of the head drop in the energy-discharge curve through large eddy simulation. The detailed analysis reveals that the head drop at the point 0.85 QBEP is related to the recirculation flow at the runner inlet. Finally, unsteady studies confirm that vortex movement at the runner inlet lead to the variation of the amplitudes and directions of the velocity, which generates the rotation of the separation vortices in the runner and stay vane channels.

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Experimental studies of unsteady cavitation at the tongue of a pump-turbine in pump mode

Renewable Energy ◽

10.1016/j.renene.2021.06.055 ◽

2021 ◽

Author(s):

Zhiyi Yuan ◽

Yongxue Zhang ◽

Jinya Zhang ◽

Jianjun Zhu

Keyword(s):

Experimental Studies ◽

Pump Mode ◽

Pump Turbine

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Distribution of Pressure Fluctuations in a Prototype Pump Turbine at Pump Mode

Advances in Mechanical Engineering ◽

10.1155/2014/923937 ◽

2014 ◽

Vol 6 ◽

pp. 923937 ◽

Cited By ~ 16

Author(s):

Yuekun Sun ◽

Zhigang Zuo ◽

Shuhong Liu ◽

Jintao Liu ◽

Yulin Wu

Keyword(s):

Mass Flow ◽

Pressure Fluctuations ◽

Dominant Frequency ◽

Pump Mode ◽

Pump Turbine ◽

Guide Vanes ◽

Path Direction ◽

Mass Flow Rates ◽

Operating Points ◽

Spiral Casing

Pressure fluctuations are very important characteristics in pump turbine's operation. Many researches have focused on the characteristics (amplitude and frequencies) of pressure fluctuations at specific locations, but little researches mentioned the distribution of pressure fluctuations in a pump turbine. In this paper, 3D numerical simulations using SSTk − ω turbulence model were carried out to predict the pressure fluctuations distribution in a prototype pump turbine at pump mode. Three operating points with different mass flow rates and different guide vanes’ openings were simulated. The numerical results show how pressure fluctuations at blade passing frequency (BPF) and its harmonics vary along the whole flow path direction, as well as along the circumferential direction. BPF is the first dominant frequency in vaneless space. Pressure fluctuation component at this frequency rapidly decays towards upstream (to draft tube) and downstream (to spiral casing). In contrast, pressure fluctuations component at 3BPF spreads to upstream and downstream with almost constant amplitude. Amplitude and frequencies of pressure fluctuations also vary along different circumferential locations in vaneless space. When the mass flow and guide vanes’ opening are different, the distribution of pressure fluctuations along the two directions is different basically.

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