The Experts below are selected from a list of 270 Experts worldwide ranked by ideXlab platform

Jian Zhang - One of the best experts on this subject based on the ideXlab platform.

  • mechanism and quantified criteria of stability characteristics of hydropower plants with Surge Tanks during regulation
    International Journal of Electrical Power & Energy Systems, 2020
    Co-Authors: Xiuwei Yang, Zhe Liu, Jian Zhang
    Abstract:

    Abstract The dynamic processes of the coupled hydro-turbine-governor system and water diversion system are complex. An inappropriate design and regulation may result in poor regulating quality and even unstable operation. This study focused on the stability characteristics of the ultra-low frequency oscillation of hydropower plants caused by the water level oscillation in Surge Tanks during regulation. The coupled system was divided into the turbine-governor-penstock subsystem (TGPS) and Surge tank-headrace tunnel subsystem (STHS) and their magnitude-frequency characteristics were presented respectively. Based on the two subsystems, the stability mechanism of the coupled system was explained by using the oscillation superposition method and a physically based and quantified criteria “superimposed magnitude” was proposed. Then, the influence mechanism of some dominant factors on the regulating stability were analyzed. The results indicated that the stability characteristics depended on the superimposed magnitude of the coupled system. When the superimposed magnitude of the combined TGPS and STHS is greater than 1, the oscillation continuously enlarges and results in instability. Meanwhile, the value of the superimposed magnitude can quantify the regulation quality. Furthermore, increasing the Surge tank area or head loss coefficient of the headrace tunnel can reduce the superimposed magnitude, resulting in the improvement of system stability.

  • stability analysis of hydro turbine governing system including Surge Tanks under interconnected operation during small load disturbance
    Renewable Energy, 2019
    Co-Authors: Xiuwei Yang, Jian Zhang
    Abstract:

    Abstract The operating modes of hydro-turbines have a significant influence on the stability of hydropower plants. In this study, a linking method of multiple hydropower plants and the frequency equation of the interconnected system are proposed. The state space modeling of the hydro-turbine governing system (HTGS), including the pipe system and Surge Tanks, is established under interconnected operating modes. The proposed model is used to simulate the small fluctuation process under isolated and interconnected operations based on the parameters of two simulated hydropower plants. The stability of the systems under different operating conditions is compared, and the effect of Surge tank area on the stable region is analyzed. The results indicate greater stability under interconnected operating conditions because of the change in regulating modes of the turbines. A hydropower plant with a smaller proportion of the total output has an insignificant effect on the system when the interconnected system is properly stable. In addition, the difference in the Surge tank periods should be maintained outside the adverse range.

  • influence of flow field on stability of throttled Surge Tanks with standpipe
    Journal of Hydrodynamics, 2013
    Co-Authors: Jian Feng An, Xiaodong Yu, Jian Zhang, Sheng Chen
    Abstract:

    The steady-state flow field characteristics have important effects on the stability of the throttled Surge tank with the standpipe. This paper analyzes these effects on the basis of the numerical simulation of the flow field by using the Computational Fluid Dynamics (CFD) method. It is shown that the anticlockwise recirculation zone is formed in the standpipe, which affects the local head loss at the junction of the standpipe with the pipeline. The variation of the head loss coefficient at the junction is linearly related with the diameter ratio of the standpipe to the pipeline. The dimensionless recirculation flow rate is proportional to the square of the diameter ratio. Considering the effects of the recirculation zone, an empirical expression of the critical stability area is obtained. Comparing with the Thoma critical area, the area obtained by the present method is smaller, and the reduction depends on the diameter ratio and the ratio of the velocity head to the head losses in the tunnel.

  • coefficients of local head losses in steady state flow of throttled Surge Tanks with standpipe by cfd
    Advanced Materials Research, 2013
    Co-Authors: Jian Feng An, Jian Zhang, Sheng Cheng
    Abstract:

    This study investigates the steady-state flow pattern of throttled Surge Tanks with standpipe, especially the coefficients of local head losses. The experiments were carried out, and FLUENT, which solves the Reynolds-averaged Navier-Stokes equations, was applied to experimental data for solving flow fields. The results show the computed and measured local head losses agree closely. The coefficients of the local head losses are linearly proportional to diameter ratio with the slope of 0.037. The anticlockwise backflow region occurs in the standpipe, and it induces inflow into and outflow from the standpipe. For hydraulic engineering projects, the discharge into and out from standpipe does not change with velocity and diameter of main conduit, but are linearly proportional to diameter ratio with the slope of 0.0378.

  • coefficients of local head losses in steady state flow of throttled Surge Tanks with standpipe by cfd
    Advanced Materials Research, 2013
    Co-Authors: Jian Feng An, Jian Zhang, Sheng Cheng
    Abstract:

    This study investigates the steady-state flow pattern of throttled Surge Tanks with standpipe, especially the coefficients of local head losses. The experiments were carried out, and FLUENT, which solves the Reynolds-averaged Navier-Stokes equations, was applied to experimental data for solving flow fields. The results show the computed and measured local head losses agree closely. The coefficients of the local head losses are linearly proportional to diameter ratio with the slope of 0.037. The anticlockwise backflow region occurs in the standpipe, and it induces inflow into and outflow from the standpipe. For hydraulic engineering projects, the discharge into and out from standpipe does not change with velocity and diameter of main conduit, but are linearly proportional to diameter ratio with the slope of 0.0378.

Wencheng Guo - One of the best experts on this subject based on the ideXlab platform.

  • A Review of the Transient Process and Control for a Hydropower Station with a Super Long Headrace Tunnel
    MDPI AG, 2018
    Co-Authors: Wencheng Guo, Daoyi Zhu
    Abstract:

    The hydropower station with a super long headrace tunnel is a significant development type for hydropower energy. By constructing a super long headrace tunnel, the huge natural water fall head can be utilized to generate more electricity. With the development of hydropower energy, a hydropower station with a super long headrace tunnel becomes more and more competitive. Compared with a hydropower station with a short headrace tunnel, the transient process and control for a hydropower station with a super long headrace tunnel is much more complicated and becomes an intractable challenge. It is well known that the transient process and control is the basis of the design and operation of a hydropower station. To overcome the challenge of the transient process and control, much research has been carried out. This paper provides a systematic review on the latest research progress of the transient process and control for hydropower stations with a super long headrace tunnel. Firstly, two key issues for the transient process and control, i.e., hydraulic design optimization of the Surge tank and operation control of unit, are illuminated. Secondly, for both single Surge Tanks and Surge Tanks with special types or combinations, the hydraulic design optimization methods are described. The most disadvantageous design and advantageous operation of Surge Tanks under combined operating conditions are discussed. Thirdly, the stability and regulation quality of the hydro-turbine governing system under isolated and grid-connected operation conditions are presented. Finally, some trends and recommendations for future research directions are made. A research thought for establishing the complete theory and application system of the transient process and control for hydropower stations with a super long headrace tunnel from the perspective of multi-slice and multi-scale is proposed

  • Surge wave characteristics for hydropower station with upstream series double Surge Tanks in load rejection transient
    Renewable Energy, 2017
    Co-Authors: Jiandong Yang, Wencheng Guo, Yi Teng
    Abstract:

    In order to reveal the Surge wave characteristics and provide design guidances for the hydropower station with upstream series double Surge Tanks in load rejection transient, this paper studies the water level oscillations in the Surge Tanks. Firstly, the mathematical model that describes the unsteady flow for pipelines system is established. Then, for undamped upstream series double Surge Tanks system, the water level oscillations in two Surge Tanks are studied by deriving the analytical formulas with a novel method and analyzing the oscillation characteristics and superposition mechanism of water levels. The effects of damping on water level oscillations are analyzed. Finally, the application guidances of the results for the design of Surge Tanks and headrace tunnels are proposed. It is demonstrated that: Under the assumption of step discharge change in penstock, the proposed method for the derivation of analytical formulas for water level oscillations is effective, and the obtained analytical formulas are reasonable and have good accuracy. For the water level oscillations in two Surge Tanks, there are two kinds of frequency for the subwaves (i.e. subwave 1 and subwave 2). Subwave 1 and subwave 2 are the fundamental wave and the harmonic wave, respectively. The amplitude of subwave 1 determines the basic range of the water level oscillation. The damping mainly affects the attenuation of the water level oscillations. The analysis results for Surge wave characteristics can be applied to the design of real projects.

  • Simulation of Wind Speed in the Ventilation Tunnel for Surge Tanks in Transient Processes
    Energies, 2016
    Co-Authors: Jiandong Yang, Weijia Yang, Wencheng Guo, Huang Wang, Wei Zeng
    Abstract:

    Hydroelectric power plants’ open-type Surge Tanks may be built in mountains subject to the provision of atmospheric air. Hence, a ventilation tunnel is indispensable. The air flow in the ventilation tunnel is associated with the fluctuation of water-level in the Surge tank. There is a great relationship between the wind speed and the safe use and project investment of ventilation tunnels. To obtain the wind speed in a ventilation tunnel for a Surge tank during transient processes, this article adopts the one-dimensional numerical simulation method and establishes a mathematical model of a wind speed by assuming the boundary conditions of air discharge for a Surge tank. Thereafter, the simulation of wind speed in a ventilation tunnel, for the case of a Surge tank during transient processes, is successfully realized. Finally, the effective mechanism of water-level fluctuation in a Surge tank and the shape of the ventilation tunnel (including length, sectional area and dip angle) for the wind speed distribution and the change process are discovered. On the basis of comparison between the simulation results of 1D and 3D computational fluid dynamics (CFD), the results indicate that the one-dimensional simulation method as proposed in this article can be used to accurately simulate the wind speed in the ventilation tunnel of a Surge tank during transient processes. The wind speed fluctuations can be superimposed by using the low frequency mass wave ( i.e. , fundamental wave) and the high frequency elastic wave ( i.e. , harmonic wave). The water-level fluctuation in a Surge tank and the sectional area of the ventilation tunnel mainly affect the amplitude of fundamental and harmonic waves. The period of a fundamental wave can be determined from the water-level fluctuations. The length of the ventilation tunnel has an effect on the period and amplitude of harmonic waves, whereas the dip angle influences the amplitude of harmonic waves.

Weijia Yang - One of the best experts on this subject based on the ideXlab platform.

  • condition of setting Surge Tanks in hydropower plants a review
    Renewable & Sustainable Energy Reviews, 2018
    Co-Authors: Haiyan Bao, Jiandong Yang, Guilian Zhao, Wei Zeng, Yanna Liu, Weijia Yang
    Abstract:

    Abstract Hydropower plays an important role in the safe, stable and efficient operation of power systems, especially with current trends toward renewable energy systems. The total global potential of gross, technical, economic, and exploitable hydropower are still enormous in the future, and the developments of new hydropower stations (HPSs) are of great importance. For constructions of new HPSs, the condition of setting Surge Tanks (CSST) is crucial for various perspectives, e.g. safety, stability and economy of HPSs. In this review, the CSST are summarized and analyzed from the three aspects: regulation assurance, operation stability, and the regulation quality, with an aim of providing a reference and guidance for research and engineering applications regarding Surge Tanks. Upstream and downstream Surge Tanks in conventional HPSs and pumped storage power stations are all included. Moreover, a comprehensive comparison of CSST under different conditions is conducted. One of the main focuses of this review is on Chinese studies, for introducing many meaningful results written in Chinese to more readers all over the world.

  • Condition of setting Surge Tanks in hydropower plants – A review
    Renewable & Sustainable Energy Reviews, 2017
    Co-Authors: Haiyan Bao, Jiandong Yang, Guilian Zhao, Wei Zeng, Yanna Liu, Weijia Yang
    Abstract:

    Abstract Hydropower plays an important role in the safe, stable and efficient operation of power systems, especially with current trends toward renewable energy systems. The total global potential of gross, technical, economic, and exploitable hydropower are still enormous in the future, and the developments of new hydropower stations (HPSs) are of great importance. For constructions of new HPSs, the condition of setting Surge Tanks (CSST) is crucial for various perspectives, e.g. safety, stability and economy of HPSs. In this review, the CSST are summarized and analyzed from the three aspects: regulation assurance, operation stability, and the regulation quality, with an aim of providing a reference and guidance for research and engineering applications regarding Surge Tanks. Upstream and downstream Surge Tanks in conventional HPSs and pumped storage power stations are all included. Moreover, a comprehensive comparison of CSST under different conditions is conducted. One of the main focuses of this review is on Chinese studies, for introducing many meaningful results written in Chinese to more readers all over the world.

  • Simulation of Wind Speed in the Ventilation Tunnel for Surge Tanks in Transient Processes
    Energies, 2016
    Co-Authors: Jiandong Yang, Weijia Yang, Wencheng Guo, Huang Wang, Wei Zeng
    Abstract:

    Hydroelectric power plants’ open-type Surge Tanks may be built in mountains subject to the provision of atmospheric air. Hence, a ventilation tunnel is indispensable. The air flow in the ventilation tunnel is associated with the fluctuation of water-level in the Surge tank. There is a great relationship between the wind speed and the safe use and project investment of ventilation tunnels. To obtain the wind speed in a ventilation tunnel for a Surge tank during transient processes, this article adopts the one-dimensional numerical simulation method and establishes a mathematical model of a wind speed by assuming the boundary conditions of air discharge for a Surge tank. Thereafter, the simulation of wind speed in a ventilation tunnel, for the case of a Surge tank during transient processes, is successfully realized. Finally, the effective mechanism of water-level fluctuation in a Surge tank and the shape of the ventilation tunnel (including length, sectional area and dip angle) for the wind speed distribution and the change process are discovered. On the basis of comparison between the simulation results of 1D and 3D computational fluid dynamics (CFD), the results indicate that the one-dimensional simulation method as proposed in this article can be used to accurately simulate the wind speed in the ventilation tunnel of a Surge tank during transient processes. The wind speed fluctuations can be superimposed by using the low frequency mass wave ( i.e. , fundamental wave) and the high frequency elastic wave ( i.e. , harmonic wave). The water-level fluctuation in a Surge tank and the sectional area of the ventilation tunnel mainly affect the amplitude of fundamental and harmonic waves. The period of a fundamental wave can be determined from the water-level fluctuations. The length of the ventilation tunnel has an effect on the period and amplitude of harmonic waves, whereas the dip angle influences the amplitude of harmonic waves.

Jiandong Yang - One of the best experts on this subject based on the ideXlab platform.

  • condition of setting Surge Tanks in hydropower plants a review
    Renewable & Sustainable Energy Reviews, 2018
    Co-Authors: Haiyan Bao, Jiandong Yang, Guilian Zhao, Wei Zeng, Yanna Liu, Weijia Yang
    Abstract:

    Abstract Hydropower plays an important role in the safe, stable and efficient operation of power systems, especially with current trends toward renewable energy systems. The total global potential of gross, technical, economic, and exploitable hydropower are still enormous in the future, and the developments of new hydropower stations (HPSs) are of great importance. For constructions of new HPSs, the condition of setting Surge Tanks (CSST) is crucial for various perspectives, e.g. safety, stability and economy of HPSs. In this review, the CSST are summarized and analyzed from the three aspects: regulation assurance, operation stability, and the regulation quality, with an aim of providing a reference and guidance for research and engineering applications regarding Surge Tanks. Upstream and downstream Surge Tanks in conventional HPSs and pumped storage power stations are all included. Moreover, a comprehensive comparison of CSST under different conditions is conducted. One of the main focuses of this review is on Chinese studies, for introducing many meaningful results written in Chinese to more readers all over the world.

  • Condition of setting Surge Tanks in hydropower plants – A review
    Renewable & Sustainable Energy Reviews, 2017
    Co-Authors: Haiyan Bao, Jiandong Yang, Guilian Zhao, Wei Zeng, Yanna Liu, Weijia Yang
    Abstract:

    Abstract Hydropower plays an important role in the safe, stable and efficient operation of power systems, especially with current trends toward renewable energy systems. The total global potential of gross, technical, economic, and exploitable hydropower are still enormous in the future, and the developments of new hydropower stations (HPSs) are of great importance. For constructions of new HPSs, the condition of setting Surge Tanks (CSST) is crucial for various perspectives, e.g. safety, stability and economy of HPSs. In this review, the CSST are summarized and analyzed from the three aspects: regulation assurance, operation stability, and the regulation quality, with an aim of providing a reference and guidance for research and engineering applications regarding Surge Tanks. Upstream and downstream Surge Tanks in conventional HPSs and pumped storage power stations are all included. Moreover, a comprehensive comparison of CSST under different conditions is conducted. One of the main focuses of this review is on Chinese studies, for introducing many meaningful results written in Chinese to more readers all over the world.

  • Surge wave characteristics for hydropower station with upstream series double Surge Tanks in load rejection transient
    Renewable Energy, 2017
    Co-Authors: Jiandong Yang, Wencheng Guo, Yi Teng
    Abstract:

    In order to reveal the Surge wave characteristics and provide design guidances for the hydropower station with upstream series double Surge Tanks in load rejection transient, this paper studies the water level oscillations in the Surge Tanks. Firstly, the mathematical model that describes the unsteady flow for pipelines system is established. Then, for undamped upstream series double Surge Tanks system, the water level oscillations in two Surge Tanks are studied by deriving the analytical formulas with a novel method and analyzing the oscillation characteristics and superposition mechanism of water levels. The effects of damping on water level oscillations are analyzed. Finally, the application guidances of the results for the design of Surge Tanks and headrace tunnels are proposed. It is demonstrated that: Under the assumption of step discharge change in penstock, the proposed method for the derivation of analytical formulas for water level oscillations is effective, and the obtained analytical formulas are reasonable and have good accuracy. For the water level oscillations in two Surge Tanks, there are two kinds of frequency for the subwaves (i.e. subwave 1 and subwave 2). Subwave 1 and subwave 2 are the fundamental wave and the harmonic wave, respectively. The amplitude of subwave 1 determines the basic range of the water level oscillation. The damping mainly affects the attenuation of the water level oscillations. The analysis results for Surge wave characteristics can be applied to the design of real projects.

  • Simulation of Wind Speed in the Ventilation Tunnel for Surge Tanks in Transient Processes
    Energies, 2016
    Co-Authors: Jiandong Yang, Weijia Yang, Wencheng Guo, Huang Wang, Wei Zeng
    Abstract:

    Hydroelectric power plants’ open-type Surge Tanks may be built in mountains subject to the provision of atmospheric air. Hence, a ventilation tunnel is indispensable. The air flow in the ventilation tunnel is associated with the fluctuation of water-level in the Surge tank. There is a great relationship between the wind speed and the safe use and project investment of ventilation tunnels. To obtain the wind speed in a ventilation tunnel for a Surge tank during transient processes, this article adopts the one-dimensional numerical simulation method and establishes a mathematical model of a wind speed by assuming the boundary conditions of air discharge for a Surge tank. Thereafter, the simulation of wind speed in a ventilation tunnel, for the case of a Surge tank during transient processes, is successfully realized. Finally, the effective mechanism of water-level fluctuation in a Surge tank and the shape of the ventilation tunnel (including length, sectional area and dip angle) for the wind speed distribution and the change process are discovered. On the basis of comparison between the simulation results of 1D and 3D computational fluid dynamics (CFD), the results indicate that the one-dimensional simulation method as proposed in this article can be used to accurately simulate the wind speed in the ventilation tunnel of a Surge tank during transient processes. The wind speed fluctuations can be superimposed by using the low frequency mass wave ( i.e. , fundamental wave) and the high frequency elastic wave ( i.e. , harmonic wave). The water-level fluctuation in a Surge tank and the sectional area of the ventilation tunnel mainly affect the amplitude of fundamental and harmonic waves. The period of a fundamental wave can be determined from the water-level fluctuations. The length of the ventilation tunnel has an effect on the period and amplitude of harmonic waves, whereas the dip angle influences the amplitude of harmonic waves.

  • Simulation of Water Level Fluctuations in a Hydraulic System Using a Coupled Liquid-Gas Model
    MDPI AG, 2015
    Co-Authors: Chao Wang, Jiandong Yang, Håkan Nilsson
    Abstract:

    A model for simulating vertical water level fluctuations with coupled liquid and gas phases is presented. The Preissmann implicit scheme is used to linearize the governing equations for one-dimensional transient flow for both liquid and gas phases, and the linear system is solved using the chasing method. Some classical cases for single liquid and gas phase transients in pipelines and networks are studied to verify that the proposed methods are accurate and reliable. The implicit scheme is extended using a dynamic mesh to simulate the water level fluctuations in a U-tube and an open Surge tank without consideration of the gas phase. Methods of coupling liquid and gas phases are presented and used for studying the transient process and interaction between the phases, for gas phase limited in a chamber and gas phase transported in a pipeline. In particular, two other simplified models, one neglecting the effect of the gas phase on the liquid phase and the other one coupling the liquid and gas phases asynchronously, are proposed. The numerical results indicate that the asynchronous model performs better, and are finally applied to a hydropower station with Surge Tanks and air shafts to simulate the water level fluctuations and air speed

Pedram Tazraei - One of the best experts on this subject based on the ideXlab platform.

  • numerical analysis of the hydraulic transient response in the presence of Surge Tanks and relief valves
    Renewable Energy, 2017
    Co-Authors: Alireza Riasi, Pedram Tazraei
    Abstract:

    Water hammer as a critical consequence of unsteadiness may take place in the penstock of the hydroelectric power plants. Hence, the unsteady flow analysis is important to identify undesirable pressure variations and to take preventive actions toward guaranteeing safe operation of the power plant. Chief among these actions are the installation of a Surge tank and relief valve, and the transient flow behavior in the presence of protective devices is investigated herein. The method of characteristics is employed to numerically solve the equations governing the transient flow through channels. Also, in order to better resolve the transient behavior, unsteady friction effects have been considered. Validation of the developed computational code is carried out through comparison of the computed transient pressures with those measured at Karun-III Hydropower Plant. According to the results obtained for MONJ Hydropower Station, when only one turbine is in operation, the Surge tank decreases the pressure rise within the spiral case and the turbine overspeed by 22% and 6%, respectively. While the percentages associated with employing a proper Surge relief valves are accordingly 12% and 14%. This study substantiates how Surge relief valves can be used instead of an expensive Surge tank to relieve the transient response.