Entropy production analysis of hysteresis characteristic of a pump-turbine model

Li, Deyou; Wang, Hongjie; Qin, Yonglin; Han, Lina; Wei, Xianzhu; Qin, Daqing

doi:10.1016/j.enconman.2017.07.024

Cited by 262 publications

(87 citation statements)

References 22 publications

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“…Since the internal energy dissipation near the wall could not be calculated accurately from the above-mentioned method, when y + value was larger than 50 [44], an approximation for the internal power loss near the wall, was defined as Equation (20).…”

Section: Dtmentioning

confidence: 99%

Unsteady Flow Numerical Simulations on Internal Energy Dissipation for a Low-Head Centrifugal Pump at Part-Load Operating Conditions

et al. 2019

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Dredge pumps are usually operated at part-load conditions, in which the low-solidity centrifugal impeller could experience large internal energy dissipation, related to flow separation and vortices. In this study, SST k-ω and SAS-SST turbulence models were used, in steady and unsteady simulations, for a low-head centrifugal pump with a three-bladed impeller. The main focus of the present work was to investigate the internal energy dissipation in rotating an impeller at part-load operating conditions, related to flow separation and stall. The unsteady nature of these operating conditions was investigated. Performance experiments and transient wall pressure measurements were conducted for validation. A methodology for internal energy dissipation analysis has been proposed; and the unsteady pressure fluctuations were analyzed in the rotating impeller. The internal power losses in the volute and the impeller were mostly found in the centrifugal pump. The rotating stall phenomenon occurred with flow separation and detachment at the part-load operating condition, leading to a dissipation of the internal energy in the impeller. The rotating impeller experienced pressure fluctuations with low frequencies, at part-load operating conditions, while in the design operating condition only experienced rotating frequency.The energy loss in the centrifugal pump could be divided into flow dissipation, disk friction, and discharge leakage loss. Kara Omar et al. [7] calculated the losses through empirical and semi-empirical models, and verified them with experimental results. El-Naggar [8] conducted an experimental one-dimensional flow analysis and predicted the pump performance in a dimensionless form. Klas et al. [9] performed simulations on a centrifugal pump and investigated the energy loss in different flow components, to detect the influence of the component geometry. These studies focused on the whole energy transformation in flow components, without a detailed loss analysis.The inner flow characteristic was investigated as the energy loss reasons for centrifugal pumps. Posa et al. [10] investigated the streamline distribution on the impeller blade surface and found that a stall phenomenon developed near the impeller shroud. Zhang et al. [11] applied velocity vector distribution to detect the flow pattern near the volute tongue, and to discuss its effects on the efficiency fluctuation of a centrifugal pump. Barrio et al. [12] detected a counter-rotating vortex near the interface between the impeller and the volute, through velocity distribution. Pacot et al. [13] used the pressure distribution to explore the stall propagation mechanism. Asim et al. [14] applied the Q-criterion to illustrate that a secondary flow generated near the volute tongue, with an impact on the pump head. Miorini et al. [15] and Zhou et al.[16] adopted a vorticity study to investigate tip leakage flow and rotating stall, respectively, to describe the development of these unsteady flow phenomena and to prove their effects on pump performance. These m...

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Section: Dtmentioning

confidence: 99%

Unsteady Flow Numerical Simulations on Internal Energy Dissipation for a Low-Head Centrifugal Pump at Part-Load Operating Conditions

et al. 2019

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“…They found that the distance affects the efficiency of the pump under positive rotation conditions and that the main mechanical energy dissipation is turbulent dissipation. Deyou Li et al [8,9] applied the entropy generation method to analyze hysteresis characteristics of a pump-turbine model and reflected the mechanical energy dissipation directly. Their analysis revealed that the mechanical energy dissipation of the runner and guide vane resulted in hump characteristics, and dissipation was mostly in the runner.…”

Section: Introductionmentioning

confidence: 99%

“…The above studies adopting the entropy generation method to investigate mechanical energy dissipation [4][5][6][7][8][9] were conducted for turbines or centrifugal pumps. Meanwhile, the main focus of our research is the exact magnitudes and distributions of mechanical energy dissipation under varying discharge and tip clearance using the entropy generation method near the hump region for an axial-flow pump.…”

Section: Introductionmentioning

confidence: 99%

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Numerical Analysis of Mechanical Energy Dissipation for an Axial-Flow Pump Based on Entropy Generation Theory

Shen

2019

Energies

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Mechanical energy dissipation is a major problem affecting hydraulic machinery especially under partial-load conditions. Owing to limitations of traditional methods in evaluating mechanical energy dissipation, entropy generation theory is introduced to study mechanical energy dissipation with varying discharge and tip clearance intuitively through numerical simulations in an axial-flow pump. Results show that the impeller and diffuser are the main domains of mechanical energy dissipation, respectively accounting for 35.32%–55.51% and 32.61%–20.42% of mechanical energy dissipation throughout the flow passage. The mechanical energy dissipation of the impeller has a strong relation with the hump characteristic and becomes increasingly important with decreasing discharge. Areas of high turbulent dissipation in the impeller are mainly concentrated near the blades’ suction sides, and these regions, especially areas near the shroud, extend with decreasing discharge. When the pump enters the hump region, the distributions of turbulent dissipation near the shroud become disordered and expand towards the impeller’s inlet side. Unstable flows, like flow separation and vortices, near the blades’ suction sides lead to the high turbulent dissipation in the impeller and hump characteristic. Turbulent dissipation at the tip decreases from the blade leading edge to trailing edge, and regions of high dissipation distribute near the leading edge of the blade tip side. An increase in tip clearance for the same discharge mainly increases areas of high turbulent dissipation near the shroud and at the tip of the impeller, finally reducing pump performance.

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“…A conventional method to deal with the transient conditions of the pumped storage unit has been to optimize the GVCS. For instance, a nonoptimal GVCS under extreme conditions causes the WHP and RSRR to rise and exceed the allowable range of design, thus resulting in unfavorable phenomena such as overspeed of the unit, abnormal vibration, and asynchronization of the movable guide vanes [13,14]. is would be a serious threat to the safety of the PSPS especially when it is under the pump outage condition, since the RSRR of the unit will increase greatly and lead to the significant change of flow rate, increasing the WHP.…”

Section: Introductionmentioning

confidence: 99%

Analysis on Guide Vane Closure Schemes of High‐Head Pumped Storage Unit during Pump Outage Condition

Zhang

Zheng

et al. 2019

Mathematical Problems in Engineering

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When the pumping operation of pumped storage unit suffers from power outage, the hydraulic transient poses a serious threat to the safe operation of the unit and its pressure pipeline system. For high-head pumped storage power station (PSPS), the water hammer pressure (WHP) and rotational speed rise ratio (RSRR) of each hydraulic unit will be increased during the pump outage condition. In order to limit the fluctuation of rotational speed and WHP in power-off condition, optimizing and choosing a reasonable guide vane closure scheme (GVCS) is an economic and efficient means to improve the dynamic characteristics of pumped storage unit. On the basis of the calculation model of the transition process of single tube-double unit type of a high-head PSPS, an optimization model of GVCS balancing WHP and RSRR objectives is established. Furthermore, the two-stage broken line and three-stage delayed GVCSs are applied to the pump outage condition, and the nondominated sorting genetic algorithm-II (NSGA-II) is introduced to calculate the optimal solution set under different water heads and different closure schemes. For four typical water heads, the multiobjective optimization results of the closure law show that the two-stage broken line law has a better Pareto front under high water head, while the three-stage delayed law has a better performance under low water head. Furthermore, through the results of transition process of typical schemes, the adaptability of GVCS and water head is analyzed. The method proposed in this paper can make the RSRR not more than −0.89, and the three-stage delayed law can even make the RSRR only −0.01. Methods of this paper provide a theoretical basis for optimum guide vane closure mode setting of PSPS.

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Entropy production analysis of hysteresis characteristic of a pump-turbine model

Cited by 262 publications

References 22 publications

Unsteady Flow Numerical Simulations on Internal Energy Dissipation for a Low-Head Centrifugal Pump at Part-Load Operating Conditions

Unsteady Flow Numerical Simulations on Internal Energy Dissipation for a Low-Head Centrifugal Pump at Part-Load Operating Conditions

Numerical Analysis of Mechanical Energy Dissipation for an Axial-Flow Pump Based on Entropy Generation Theory

Analysis on Guide Vane Closure Schemes of High‐Head Pumped Storage Unit during Pump Outage Condition

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