Suppression of flow instability in draft tube of Pump Turbine using J-Groove

Pumped-storage power stations play a regulatory role in the power grid through frequent transition processes. The pressure pulsation in the draft tube of the pump-turbine under transient processes is important for safe operation, which is more intense than that in the steady-state condition. However, there is no effective method to obtain the exact pressure in the draft tube in the transient flow field. In this paper, the pressure in the draft tube of a pump-turbine under steady-state and transient conditions are studied by means of CFD. The reliability of the simulation method is verified by comparing the real pressure pulsation data with the test results. Due to the distribution of the pressure pulsation in the draft tube being complex and uneven, the location of the pressure monitoring points directly affects the accurate judgement of cavitation. Eight monitoring surfaces were set in the straight cone of the draft tube and nine monitoring points were set on each monitoring surface to analyze the pressure differences on the wall and inside the center of the draft tube. The relationships between the pressure pulsation value inside the center of the draft tube and on the wall are studied. The “critical” wall pressure pulsation value when cavitation occurs is obtained. This study provides references for judging cavitation occurrences by using the wall pressure pulsation value in practical engineering.

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Manipulation of the swirling flow instability in hydraulic turbine diffuser by different methods of water injection

EPJ Web of Conferences ◽

10.1051/epjconf/201818002090 ◽

2018 ◽

Vol 180 ◽

pp. 02090 ◽

Cited By ~ 1

Author(s):

Pavel Rudolf ◽

Jiří Litera ◽

Germán Alejandro Ibarra Bolanos ◽

David Štefan

Keyword(s):

Swirling Flow ◽

Flow Instability ◽

Draft Tube ◽

Water Injection ◽

Hydraulic Turbine ◽

Operating Conditions ◽

Francis Turbine ◽

Necessary Condition ◽

Vortex Rope ◽

Wide Range

Vortex rope, which induces substantial pressure pulsations, arises in the draft tube (diffuser) of Francis turbine for off-design operating conditions. Present paper focuses on mitigation of those pulsations using active water jet injection control. Several modifications of the original Susan-Resiga’s idea were proposed. All modifications are driven by manipulation of the shear layer region, which is believed to play important role in swirling flow instability. While some of the methods provide results close to the original one, none of them works in such a wide range. Series of numerical experiments support the idea that the necessary condition for vortex rope pulsation mitigation is increasing the fluid momentum along the draft tube axis.

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Pressure fluctuation and flow instability in S-shaped region of a reversible pump-turbine

Renewable Energy ◽

10.1016/j.renene.2020.03.069 ◽

2020 ◽

Vol 154 ◽

pp. 826-840 ◽

Cited By ~ 1

Author(s):

Wenwu Zhang ◽

Zhenmu Chen ◽

Baoshan Zhu ◽

Fei Zhang

Keyword(s):

Pressure Fluctuation ◽

Flow Instability ◽

Pump Turbine

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Flow instability transferability characteristics within a reversible pump turbine (RPT) under large guide vane opening (GVO)

Renewable Energy ◽

10.1016/j.renene.2021.07.039 ◽

2021 ◽

Author(s):

Maxime Binama ◽

Kan Kan ◽

Hui-Xiang Chen ◽

Yuan Zheng ◽

Daqing Zhou ◽

...

Keyword(s):

Flow Instability ◽

Guide Vane ◽

Pump Turbine

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Influences of Rotational Speed Variations on the Flow-Induced Vibrational Performance of a Prototype Reversible Pump Turbine in Spin-No-Load Mode

Journal of Fluids Engineering ◽

10.1115/1.4045159 ◽

2019 ◽

Vol 142 (1) ◽

Author(s):

Xianghao Zheng ◽

Yuning Zhang ◽

Jinwei Li ◽

Yuning Zhang

Keyword(s):

Vibrational Level ◽

Rotational Speed ◽

Draft Tube ◽

Dominant Frequency ◽

Pump Turbine ◽

Vortex Rope ◽

Vibrational Levels ◽

Load Mode ◽

Swirling Vortex ◽

Dominant Frequencies

Abstract During the spin-no-load mode, vibrational performance of the reversible pump turbine is an important criterion for the evaluation of the operational performances of the power station. In the present paper, the influences of rotational speed variations on the vibrational performances of the whole unit (including the top cover, the upper, and the lower brackets) are experimentally investigated with discussions of their sources and propagation characteristics. According to the whole vibrational levels and the dominant frequencies of the vibration signals obtained at the top cover, the investigated cases with different rotational speeds could be divided into three partitions with their main characteristics given as follows. In the first partition (with low rotational speeds), the vibrational level is quite limited, and its source is the pressure fluctuation generated by the swirling vortex rope in the draft tube. In the second partition (with medium rotational speeds), the vibrational level gradually increases and its source is the mechanical aspects of the impeller rotation. In the third partition (with high rotational speeds), the vibrational level is prominent with a prominent swirling vortex rope in the draft tube and intensive rotor–stator interactions in the vaneless space (VS). For the vibrations of the upper and the lower brackets, the vibrations mainly originate from the mechanical aspects of the impeller rotation and the amplitudes of the dominant frequency also increase with the increment of the rotational speed. Finally, differences between the vibrational performances of the spin-no-load mode and the generating mode are discussed.

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Computational Study of Pump Turbine: Partial Load Operations

Volume 3: Computational Fluid Dynamics; Micro and Nano Fluid Dynamics ◽

10.1115/fedsm2020-20054 ◽

2020 ◽

Author(s):

Muhannad Altimemy ◽

Justin Caspar ◽

Alparslan Oztekin

Keyword(s):

Flow Rate ◽

Draft Tube ◽

Computational Study ◽

Pressure Fluctuations ◽

System Stability ◽

Pump Turbine ◽

Vortex Rope ◽

Signal Velocity ◽

Partial Load ◽

Les Model

Abstract The performance of a pump-turbine under partial flow rates, 85%, 75%, and 65%, is studied using the LES model. The power signal, velocity, vorticity, and pressure field is presented over the blades and throughout the draft tube. Pressure fluctuations are probed at various locations over the wall of the draft tube. Examining the flow field in the blade region can provide further insights into the system performance. Flow-induced pressure fluctuations can disrupt system stability. For this turbine, a strong swirling region is observed around the draft tube walls, causing pressure fluctuations. The size and intensity of this region decrease with the flow rate. A vortex rope is present in all cases. At the design point, the strength is constant throughout the draft tube. However, at partial load, the rope is weakened along the draft tube. Between the region dominated by the vortex rope and the wall, there is a swirling shear layer, which moves closer to the wall as the flow rate decreases. Both the magnitude of pressure fluctuations at the wall and the pressure difference over the blade decrease with the flow rate. The decreased pressure differences over the blade represent less power produced, and the decline in fluctuation magnitude at the wall represents more system stability. For this turbine, there appears to be a trade-off between power and strength of pressure fluctuations.

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Experimental investigation of draft tube flow instability

IOP Conference Series Earth and Environmental Science ◽

10.1088/1755-1315/12/1/012044 ◽

2010 ◽

Vol 12 ◽

pp. 012044 ◽

Cited By ~ 8

Author(s):

S Tridon ◽

S Barre ◽

G D Ciocan ◽

P Leroy ◽

C Ségoufin

Keyword(s):

Experimental Investigation ◽

Flow Instability ◽

Draft Tube ◽

Tube Flow

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Draft Tube Design and Multistage Performance of a Pump Turbine

WASSERWIRTSCHAFT ◽

10.1007/s35147-015-0514-2 ◽

2015 ◽

Vol 105 (13) ◽

pp. 38-42

Author(s):

Eduard Doujak

Keyword(s):

Draft Tube ◽

Pump Turbine

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Study on the Hydraulic Transients of Pump-Turbines Load Successive Rejection in Pumped Storage Plant

Volume 2: Fora, Parts A and B ◽

10.1115/fedsm2007-37428 ◽

2007 ◽

Cited By ~ 2

Author(s):

Jian Zhang ◽

Weihua Lu ◽

Jianyong Hu ◽

Boqin Fan

Keyword(s):

Draft Tube ◽

Maximum Pressure ◽

Hydraulic Transients ◽

Pump Turbine ◽

Hydraulic Unit ◽

Interval Time ◽

Minimum Pressure ◽

Practical Operation ◽

Water Conveyance ◽

Pumped Storage

During the calculation of hydraulic transients in pumped storage plants, the speed change of reversible pump-turbine has great relation with the pressure of water conveyance system, and results in the minimum pressure at draft tube does not occur while all sets in the same hydraulic unit reject load simultaneously, but occurs in the combined conditions of load successive rejection. Based on the hydraulic characteristic of reversible pump-turbine, the reason why the minimum pressure at draft tube occur in the combined conditions and the dangerous interval time are analyzed bonding with the water conveyance system layout of pumped storage plants and the practical operation of pump-turbine. The research indicate that when reversible turbines in the same hydraulic unit reject load successively, the maximum pressure at spiral case maybe lower to some extent compared with load rejections simultaneously, but the change of minimum pressure drop at draft tube is great along with different interval time, which endangers the water conveyance system badly, especially in high head pumped storage plants, and should be pay great attention to it. Combining the practical operation of pump-turbine with calculation in theory, it would be the dangerous interval time of load successive rejection of pump-turbines after the first pump-turbine rejects load and its runaway speed achieve speed peak, the pressure of draft tube would drop the minimum once the other set in the same hydraulic unit also reject load at the moment.

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