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The computational fluid dynamics (CFD) approach can be used to obtain both internal and external characteristics of centrifugal pumps, and the variations of the hydrodynamic force, the pressure and the torque on the blades acquired by the CFD are highly associated with the safety of the pumping system. Based on the CFD simulations, this paper investigates the stopping characteristics of multiple pumps with some pumps being stopped. The 3-D geometric model is built, including all 6 pumps, the valves, the pipes, the tanks and other components, and using the Realizable k-ε turbulence model. The CFD results for the operating points agree well with the results from the theoretical analysis. With some pumps being stopped, the key parameters of the operating pumps would not be stable, with a larger fluctuation; the direction of the hydrodynamic force might be opposite with more than 3 stopped pumps. For the stopped pumps, the maximum reverse values of the discharge and the rotational speed would be larger when fewer pumps are stopped, and could be more than 120% of the rated values, which is dangerous for the pumping system. The CFD results could help understanding the stopping process of multiple pump systems with some pumps being stopped.
Yue-Fei Liu; Jian-Xu Zhou; Qiang Guo; Ai-Li Shen; Jian Zhang. 3-D CFD simulation of transients in multiple pump system with some pumps being stopped. Journal of Hydrodynamics 2021, 33, 583 -592.
AMA StyleYue-Fei Liu, Jian-Xu Zhou, Qiang Guo, Ai-Li Shen, Jian Zhang. 3-D CFD simulation of transients in multiple pump system with some pumps being stopped. Journal of Hydrodynamics. 2021; 33 (3):583-592.
Chicago/Turabian StyleYue-Fei Liu; Jian-Xu Zhou; Qiang Guo; Ai-Li Shen; Jian Zhang. 2021. "3-D CFD simulation of transients in multiple pump system with some pumps being stopped." Journal of Hydrodynamics 33, no. 3: 583-592.
For the different types of throttled surge tanks used in hydropower systems, it is important to comprehensively know the throttle's head loss characteristics for exact surge analysis and transient control. Herein, a general and complete experimental setup was designed to steadily reproduce the 12 typical flow regimes occurring at the surge tank and thus conduct comprehensive experimental research on throttle head loss coefficients. Furthermore, an extended mathematical model for the surge tank was derived by inputting experimental data on the throttle's head loss coefficients to surge analysis. Through experimental research, the throttle's head loss coefficients were determined by fitting formulae relative to the different flow regimes and discharge ratios; via a detailed case analysis, the differences in the head loss characteristics for different throttle types were accurately determined. It was demonstrated that the throttle's head loss coefficient varies with discharge ratio under different flow regimes and found that the experimentally obtained flow coefficients for different throttle types are more accurate and clearly reveal the difference of throttles’ head loss characteristics. The extended mathematical model for the throttled surge tank can provide more accurate simulation results and guidance for its engineering design and layout.
Jianxu Zhou; Sunit Palikhe; Fulin Cai; Yuefei Liu. Experimental and simulation‐based investigations on throttle’s head loss coefficients of a surge tank. Energy Science & Engineering 2020, 8, 2722 -2733.
AMA StyleJianxu Zhou, Sunit Palikhe, Fulin Cai, Yuefei Liu. Experimental and simulation‐based investigations on throttle’s head loss coefficients of a surge tank. Energy Science & Engineering. 2020; 8 (8):2722-2733.
Chicago/Turabian StyleJianxu Zhou; Sunit Palikhe; Fulin Cai; Yuefei Liu. 2020. "Experimental and simulation‐based investigations on throttle’s head loss coefficients of a surge tank." Energy Science & Engineering 8, no. 8: 2722-2733.
Fluid–structure interaction (FSI) is a frequent and unstable inherent phenomenon in water conveyance systems. Especially in a system with a surge chamber, valve closing and the subsequent water level oscillation in the surge chamber are the excitation source of the hydraulic transient process. Water-hammer-induced FSI has not been considered in preceding research, and the results without FSI justify further investigations. In this study, an FSI eight-equation model is presented to capture its influence. Both the elbow pipe and surge chamber are treated as boundary conditions, and solved using the finite volume method (FVM). After verifying the feasibility of using FVM to solve FSI, friction, Poisson, and junction couplings are discussed in detail to separately reveal the influence of a surge chamber, tow elbows, and a valve on FSI. Results indicated that the major mechanisms of coupling are junction coupling and Poisson coupling. The former occurs in the surge chamber and elbows. Meanwhile, a stronger pressure pulsation is produced at the valve, resulting in a more complex FSI response in the water conveyance system. Poisson coupling and junction coupling are the main factors contributing to a large amount of local transilience emerging on the dynamic pressure curves. Moreover, frictional coupling leads to the lower amplitudes of transilience. These results indicate that the transilience is induced by the water hammer–structure interaction and plays important roles in the orifice optimization in the surge chamber.
Qiang Guo; Jianxu Zhou; Yongfa Li; Xiaolin Guan; DaoHua Liu; Jian Zhang. Fluid-Structure Interaction Response of a Water Conveyance System with a Surge Chamber during Water Hammer. Water 2020, 12, 1025 .
AMA StyleQiang Guo, Jianxu Zhou, Yongfa Li, Xiaolin Guan, DaoHua Liu, Jian Zhang. Fluid-Structure Interaction Response of a Water Conveyance System with a Surge Chamber during Water Hammer. Water. 2020; 12 (4):1025.
Chicago/Turabian StyleQiang Guo; Jianxu Zhou; Yongfa Li; Xiaolin Guan; DaoHua Liu; Jian Zhang. 2020. "Fluid-Structure Interaction Response of a Water Conveyance System with a Surge Chamber during Water Hammer." Water 12, no. 4: 1025.
A surge tank effectively reduces water hammer but experiences water level oscillations during transient processes. A double chamber surge tank is used in high head plants with appreciable variations in reservoir water levels to limit the maximum amplitudes of oscillation by increasing the volume of the surge tank near the extremes of oscillation. Thus, the volume of the chambers and the design of an orifice are the most important factors for controlling the water level oscillations in a double chamber surge tank. Further, maximum/minimum water level in the surge tank and damping of surge waves have conflicting behaviors. Hence, a robust optimization method is required to find the optimum volume of chambers and the diameter of the orifice of the double chamber surge tank. In this paper, the maximum upsurge, the maximum downsurge, and the damping of surge waves are considered as the objective functions for optimization. The worst condition of upsurge and downsurge is determined through 1-D numerical simulation of the hydropower system by using method of characteristics (MOC). Moreover, the sensitivity of dimensions of a double chamber surge tank is studied to find their impact on objective functions; finally, the optimum dimensions of the double chamber surge tank are found using non-dominated sorting genetic algorithm II (NSGA-II) to control the water level oscillations in the surge tank under transient processes. The volume of the optimized double chamber surge tank is only 44.53% of the total volume of the simple surge tank, and it serves as an effective limiter of maximum amplitudes of oscillations. This study substantiates how an optimized double chamber surge tank can be used in high head plants with appreciable variations in reservoir water levels.
Resham Dhakal; Jianxu Zhou; Sunit Palikhe; Khem Prasad Bhattarai. Hydraulic Optimization of Double Chamber Surge Tank Using NSGA-II. Water 2020, 12, 455 .
AMA StyleResham Dhakal, Jianxu Zhou, Sunit Palikhe, Khem Prasad Bhattarai. Hydraulic Optimization of Double Chamber Surge Tank Using NSGA-II. Water. 2020; 12 (2):455.
Chicago/Turabian StyleResham Dhakal; Jianxu Zhou; Sunit Palikhe; Khem Prasad Bhattarai. 2020. "Hydraulic Optimization of Double Chamber Surge Tank Using NSGA-II." Water 12, no. 2: 455.
In a pressurized water conveyance system, such as a hydropower system, during hydraulic transients, maximum and minimum pressures at various controlling sections are of prime concern for designing a safe and efficient surge tank. Similarly, quick damping of surge waves is also very helpful for the sound functioning of the hydro-mechanical system. Several parameters like diameter of the surge tank, diameter of the orifice, operating discharge, working head, etc., influence the maximum/minimum surge, damping of surge waves in the surge tank, and the difference of maximum pressure head at the bottom tunnel and maximum water level in the surge tank. These transient behaviors are highly conflicting in nature, especially for different diameters of orifices (DO) and diameters of surge tanks (DS). Hence, a proper optimization method is necessary to investigate the best values of DO and DS to enhance the safety and efficiency of the surge tank. In this paper, these variables are accurately determined through numerical analysis of the system by the Method of Characteristics (MOC). Furthermore, the influence on the transient behavior with changing DO and DS is investigated and finally, optimum values of DO and DS are determined using Particle Swarm Optimization (PSO) to minimize the effects of hydraulic transients on the system without compromising the stability and efficiency of the surge tank. The obtained results show significant improvements over the contemporary methods of finding DO and DS for surge tank design.
Khem Prasad Bhattarai; Jianxu Zhou; Sunit Palikhe; Kamal Prasad Pandey; Naresh Suwal. Numerical Modeling and Hydraulic Optimization of a Surge Tank Using Particle Swarm Optimization. Water 2019, 11, 715 .
AMA StyleKhem Prasad Bhattarai, Jianxu Zhou, Sunit Palikhe, Kamal Prasad Pandey, Naresh Suwal. Numerical Modeling and Hydraulic Optimization of a Surge Tank Using Particle Swarm Optimization. Water. 2019; 11 (4):715.
Chicago/Turabian StyleKhem Prasad Bhattarai; Jianxu Zhou; Sunit Palikhe; Kamal Prasad Pandey; Naresh Suwal. 2019. "Numerical Modeling and Hydraulic Optimization of a Surge Tank Using Particle Swarm Optimization." Water 11, no. 4: 715.
Hydraulic oscillation mainly reveals the undesirable pressure fluctuations which can cause catastrophic failure of any hydraulic system. The behavior of a hydraulic system equipped with two different pump-turbines was investigated through hydraulic oscillation analysis to demonstrate severe consequences induced in turbine operation, including S-shaped characteristics. The impedance of a pump-turbine has an essential role in the determination of the instability of the hydraulic system. The conventional way to determine the instability solely using the slope of a characteristic curve was improved, including the effect of guide vane opening in pump-turbine impedance, which consequently modified the instability expression. With this pump-turbine impedance, hydraulic oscillation analysis, including free oscillation analysis and frequency response analysis, was carried out. The free oscillation analysis entails the computation of complex natural frequencies and corresponding mode shapes of the system. These computations provided necessary information about the vulnerable position of vital hydraulic components and the scenario for self-excited oscillation. Further, the analysis illustrates the significant role of guide vane opening to prevent the system from becoming unstable. Lastly, frequency response analysis was performed for the system with an oscillating guide vane to obtain the frequency response spectrum, which revealed that the resonating frequencies are consistent with natural frequencies, and it supported free oscillation results.
Sunit Palikhe; Jianxu Zhou; Khem Prasad Bhattarai. Hydraulic Oscillation and Instability of a Hydraulic System with Two Different Pump-Turbines in Turbine Operation. Water 2019, 11, 692 .
AMA StyleSunit Palikhe, Jianxu Zhou, Khem Prasad Bhattarai. Hydraulic Oscillation and Instability of a Hydraulic System with Two Different Pump-Turbines in Turbine Operation. Water. 2019; 11 (4):692.
Chicago/Turabian StyleSunit Palikhe; Jianxu Zhou; Khem Prasad Bhattarai. 2019. "Hydraulic Oscillation and Instability of a Hydraulic System with Two Different Pump-Turbines in Turbine Operation." Water 11, no. 4: 692.
Generally, the operation of the horizontally-framed miter gate in a ship lock should consider the effects of hydrodynamic resistance. If over-filling or over-emptying exists and the miter gate opens with reverse head, the hydrodynamic resistance will increase rapidly, endangering the operation safety of the miter gate. In order to study the operating characteristics of the miter gate, a prototype test is introduced in this paper. Results show that, during the filling or emptying process, when water levels at both sides of the miter gate are equal the first time, opening the gate in a timely manner can obviously avoid the influence of reverse head. Furthermore, a three-dimensional numerical model with a dynamic mesh is established for analyzing the hydrodynamic characteristics in different operating conditions. Results show that the peak value of operating load always occurs at the initial time, and the greater the submerged water depth, the larger the peak value. With the increasing of reverse head, the piston rods sustain a great compression, and the peak value appears at an early stage of gate opening. The results have a reference value for the design of a miter gate in the related engineering projects.
Jinchao Xu; Qiong Chen; Yun Li; Jianxu Zhou; Jianfeng An; Xiujun Yan; Yan Guo. Study on the Hydrodynamic Resistance Moment of Horizontally-Framed Miter Gates. Water 2018, 10, 1345 .
AMA StyleJinchao Xu, Qiong Chen, Yun Li, Jianxu Zhou, Jianfeng An, Xiujun Yan, Yan Guo. Study on the Hydrodynamic Resistance Moment of Horizontally-Framed Miter Gates. Water. 2018; 10 (10):1345.
Chicago/Turabian StyleJinchao Xu; Qiong Chen; Yun Li; Jianxu Zhou; Jianfeng An; Xiujun Yan; Yan Guo. 2018. "Study on the Hydrodynamic Resistance Moment of Horizontally-Framed Miter Gates." Water 10, no. 10: 1345.
Hydraulic vibration exists in various water conveyance projects and has resulted in different operating problems, but its obvious effects on system’s pressure head and stable operation have not been definitively addressed in the issued codes for engineering design, especially considering the uncertainties of hydraulic vibration. After detailed analysis of the randomness in hydraulic vibration and the commonly used stochastic approaches, in the basic equations for hydraulic vibration analysis, the random parameters and the formed stochastic equations were discussed for further probabilistic characteristic analysis of the random variables. Furthermore, preliminary investigation of the stochastic analysis of hydraulic vibration in pressurized pipelines and possible self-excited vibration in pumped-storage systems was presented for further consideration. The detailed discussion indicates that it is necessary to conduct further and systematic stochastic analysis of hydraulic vibration. Further, with the obtained frequencies and amplitudes in the form of a probability statement, the stochastic characteristics of various hydraulic vibrations can be investigated in detail and these solutions will be more reasonable for practical applications. Eventually, the stochastic analysis of hydraulic vibration will provide a basic premise to introduce its effect into the engineering design of water diversion and hydropower systems.
Jianxu Zhou; Yu Chen. Discussion on Stochastic Analysis of Hydraulic Vibration in Pressurized Water Diversion and Hydropower Systems. Water 2018, 10, 353 .
AMA StyleJianxu Zhou, Yu Chen. Discussion on Stochastic Analysis of Hydraulic Vibration in Pressurized Water Diversion and Hydropower Systems. Water. 2018; 10 (4):353.
Chicago/Turabian StyleJianxu Zhou; Yu Chen. 2018. "Discussion on Stochastic Analysis of Hydraulic Vibration in Pressurized Water Diversion and Hydropower Systems." Water 10, no. 4: 353.
This paper presents for the first time observations of a self-induced sloshing phenomenon in the water-retaining weir model. Fast Fourier Transform method is used to detect the dominant frequency for the sloshing water. The characteristics of the sloshing water in terms of sloshing strength and frequency are experimentally studied for six different cases. Results show that both sloshing regions and sloshing strength depends on not only the water levels but also the inlet velocities, and the relationship between them is displayed in this paper. Different prediction models for sloshing frequencies are built and compared with the experimental results, with discussions of the differences between them. For higher water level sloshing region, a new factor is introduced to the Faltinsen’s prediction formula, leading to a better agreement between prediction and experimental results. The mechanism of the self-induced sloshing is also discussed in this paper.
Yulong Hua; Fulin Cai; Jianxu Zhou; Wen Zhang. Study of Self-Induced Sloshing in Model Test of a Water Retaining Weir. Water 2017, 9, 646 .
AMA StyleYulong Hua, Fulin Cai, Jianxu Zhou, Wen Zhang. Study of Self-Induced Sloshing in Model Test of a Water Retaining Weir. Water. 2017; 9 (9):646.
Chicago/Turabian StyleYulong Hua; Fulin Cai; Jianxu Zhou; Wen Zhang. 2017. "Study of Self-Induced Sloshing in Model Test of a Water Retaining Weir." Water 9, no. 9: 646.
Diversion tunnels are often used as tailrace tunnels in underground hydropower stations. The special layout results in complex flow regimes, including air-water two-phase flow. A set of experiments is conducted based on the model of a hydropower station which combines partial diversion tunnels with tailrace tunnels to investigate the interactions between the air and water phases in the combined diversion tunnels. Interactions between the air and water phases observed in the combined diversion tunnel significantly alter flow dynamics, and are classified into four types according to the initial tail water level. There is a range of initial tail water levels in which the interaction between the air and water phases cannot be neglected, and the range becomes greater when the change in flow rate increases. Such interactions may cause a pressure surge and the pressure surge reaches the maximum when the initial tail water level is approximately equal to the crown of the tunnel. The surge pressures do harm to the safety and stability of hydropower stations, so the condition should be considered and controlled.
Wen Zhang; Fulin Cai; Jianxu Zhou; Yulong Hua. Experimental Investigation on Air-Water Interaction in a Hydropower Station Combining a Diversion Tunnel with a Tailrace Tunnel. Water 2017, 9, 274 .
AMA StyleWen Zhang, Fulin Cai, Jianxu Zhou, Yulong Hua. Experimental Investigation on Air-Water Interaction in a Hydropower Station Combining a Diversion Tunnel with a Tailrace Tunnel. Water. 2017; 9 (4):274.
Chicago/Turabian StyleWen Zhang; Fulin Cai; Jianxu Zhou; Yulong Hua. 2017. "Experimental Investigation on Air-Water Interaction in a Hydropower Station Combining a Diversion Tunnel with a Tailrace Tunnel." Water 9, no. 4: 274.
For some special tailrace tunnels in the hydropower stations, including the changing top-altitude tailrace tunnel and the tailrace tunnel with downstream reused flat-ceiling diversion tunnel, during normal operation and hydraulic transients, the flow patterns inside are relatively complex mainly including the free-surface pressurized flow and partial free flow if the tail water level is lower than the top elevation of tunnel’s outlet. These complex flow patterns have obvious effect on system’s stability, and can not be simulated accurately by the traditional models. Therefore, a characteristic implicit model is introduced to simulate these complex flow patterns for further stability analysis. In some special cases, the characteristic implicit model also fails to completely simulate the mixed free-surface pressurized flow in the flat-ceiling tailrace tunnel. A new method is presented based on both experimental research and numerical simulation, and then, system’s stability is analyzed by compared with traditional ordinary boundary condition. The results indicate that, with different simulation models for the complex water flow in the tailrace tunnel, system’s dynamic characteristic can be actually revealed with the consideration of the effect of complex flow patterns in the tailrace tunnel on system’s stability and regulation performance.
Jianxu Zhou; Fulin Cai; Ming Hu. Stability Analysis of Hydropower Stations With Complex Flow Patterns in the Tailrace Tunnel. Volume 2, Fora: Cavitation and Multiphase Flow; Fluid Measurements and Instrumentation; Microfluidics; Multiphase Flows: Work in Progress 2013, 1 .
AMA StyleJianxu Zhou, Fulin Cai, Ming Hu. Stability Analysis of Hydropower Stations With Complex Flow Patterns in the Tailrace Tunnel. Volume 2, Fora: Cavitation and Multiphase Flow; Fluid Measurements and Instrumentation; Microfluidics; Multiphase Flows: Work in Progress. 2013; ():1.
Chicago/Turabian StyleJianxu Zhou; Fulin Cai; Ming Hu. 2013. "Stability Analysis of Hydropower Stations With Complex Flow Patterns in the Tailrace Tunnel." Volume 2, Fora: Cavitation and Multiphase Flow; Fluid Measurements and Instrumentation; Microfluidics; Multiphase Flows: Work in Progress , no. : 1.
A higher-order elastic model of the flow in long pressurized pipelines is expected to be utilized for stability analysis of the governor-turbine-hydraulic system in hydropower stations. Because traditional elastic models are limited in lower order application because of their difficult decoupling in addition to the rigid model, a new linear elastic model of the flow in pressurized pipelines is derived on the basis of the equations of hydraulic vibration, in which each oscillatory flow with a different order has been obtained with ordinary differential equations in decoupling form. For water conveyance systems with branching pipes or parallel pipes in hydropower stations, the state equations to describe hydraulic characteristics of the governor-turbine-hydraulic system are established with the application of this new elastic model for diversion pipeline flow or tail tunnel flow. The influence of the elastic models with different order on a system’s stability are revealed in detail by two cases that illustrate that an elastic model with proper order should be used for the flow in pressurized pipelines of hydropower stations, according to their length, to improve the accuracy of stability analysis.
Jianxu Zhou; Fulin Cai; Yuan Wang. New Elastic Model of Pipe Flow for Stability Analysis of the Governor-Turbine-Hydraulic System. Journal of Hydraulic Engineering 2011, 137, 1238 -1247.
AMA StyleJianxu Zhou, Fulin Cai, Yuan Wang. New Elastic Model of Pipe Flow for Stability Analysis of the Governor-Turbine-Hydraulic System. Journal of Hydraulic Engineering. 2011; 137 (10):1238-1247.
Chicago/Turabian StyleJianxu Zhou; Fulin Cai; Yuan Wang. 2011. "New Elastic Model of Pipe Flow for Stability Analysis of the Governor-Turbine-Hydraulic System." Journal of Hydraulic Engineering 137, no. 10: 1238-1247.
Based on experimental simulation and numerical analysis, the effect of operation condition and load characteristic on unitpsilas stability is further investigated in detail. An experimental system of single-unit and single-pipe hydropower station is designed and built including a simulated water pumping system (dynamic load) and a resistance (static load). Stability experiment research and further analysis is performed under two realized typical conditions that is grid interconnection operation or isolated operation. The experimental results indicate that, impact of large power grid is beneficial to operation stability, and regulation performance of unit running with dynamic load is superior to that of static load. Moreover, the solution and dynamic curves gained by experimental research is identical with that of further numerical analysis.
Jianxu Zhou; Ming Hu; Fulin Cai; Rong Hu. Experimental Research on Stability of Hydro-Mechanical-Electrical System in Hydropower Station. 2009 Asia-Pacific Power and Energy Engineering Conference 2009, 1 -4.
AMA StyleJianxu Zhou, Ming Hu, Fulin Cai, Rong Hu. Experimental Research on Stability of Hydro-Mechanical-Electrical System in Hydropower Station. 2009 Asia-Pacific Power and Energy Engineering Conference. 2009; ():1-4.
Chicago/Turabian StyleJianxu Zhou; Ming Hu; Fulin Cai; Rong Hu. 2009. "Experimental Research on Stability of Hydro-Mechanical-Electrical System in Hydropower Station." 2009 Asia-Pacific Power and Energy Engineering Conference , no. : 1-4.
For some hydropower stations with a proper length tail tunnel, if its tailrace level is varied within a certain range, changing top-altitude tail tunnel instead of tail surge tank with large area is a reasonable choice to improve the min. pressure at draft tube inlet section. After the basic differential equations were deduced based on the characteristic implicit model for the transient flow in the changing top-altitude tail tunnel and some complex boundary conditions were built, a unified algorithm tracing the separation point was given combined with characteristic method in pressurized pipeline, improved slot model in channel and mathematical method in state equations. For a given case, the hydraulic characteristic of changing top-altitude tail tunnel was analyzed by this unified algorithm and further comparison was performed with the tail surge tank plan. The results indicate that, for the changing top-altitude tail tunnel, the computational results of its large fluctuation transient process are satisfied with the requirement of regulation guaranteed computation effectively; From the viewpoint of the effect of hydraulic disturb and small fluctuation on operation unit’s stability and regulation performance, it is superior to the tail surge tank plan.
Jianxu Zhou; Qing Su; Fulin Cai; Changkuan Zhang; Hongwu Tang. Hydraulic Characteristic Analysis of Changing Top-Altitude Tail Tunnel and its Application. Advances in Water Resources and Hydraulic Engineering 2009, 2074 -2079.
AMA StyleJianxu Zhou, Qing Su, Fulin Cai, Changkuan Zhang, Hongwu Tang. Hydraulic Characteristic Analysis of Changing Top-Altitude Tail Tunnel and its Application. Advances in Water Resources and Hydraulic Engineering. 2009; ():2074-2079.
Chicago/Turabian StyleJianxu Zhou; Qing Su; Fulin Cai; Changkuan Zhang; Hongwu Tang. 2009. "Hydraulic Characteristic Analysis of Changing Top-Altitude Tail Tunnel and its Application." Advances in Water Resources and Hydraulic Engineering , no. : 2074-2079.