Reversible Turbine Research Articles

Comparative evaluation of sand erosion in reversible turbine at pump mode and turbine mode

During the operation of reversible pump turbine, the flow passing components are often worn by sediments. In this paper, Euler-Euler computational fluid dynamics (CFD) method is used to simulate the liquid-solid two-phase steady flow in several pump modes and turbine modes. Finnie models are used to predict possible wear conditions and further analyze the causes of component wear. Results show that runner is the most easily worn component, which is related to local high flow velocity. The runner erosion position is mainly concentrated in the middle part of the pressure side. The erosion position of guide vane and stay vane is mainly concentrated in the leading edge and trailing edge, which depends on the change of condition. By daily weighted, the turbine mode is found has higher erosion rate than that of pump mode. This study provides the scientific support of anti-erosion of pumped storage units.

Simulating Fish Motion through a Diagonal Reversible Turbine

Utilization of unharnessed hydro-power necessitates designing fish-friendly hydraulic machinery. Towards this effort, the present work investigates various methods for tracking fish motion, ranging from particle tracking methods to accurate, but computationally expensive, body tracking methods, such as immersed boundaries and overset meshes. Moreover, a novel uncoupled 6-Degree of Freedom tracking technique is proposed, based on an approximated pressure field around the tracked body of interest, using steady-state flow field data, and including collision detection to walls. The proposed method shows promising results in terms of accuracy, being comparable to the more computationally expensive fully coupled methods at a tiny fraction of the execution time. The new method reveals location of fish–blade impact, as well as statistics of forces, pressure and flow shear that a passing fish is subjected to, both in the normal and reverse operation of the turbine. The low computational cost of the proposed method renders it attractive for optimization studies.

Unsteady computational fluid dynamics analysis of the hydrodynamic instabilities in a reversible Francis turbine used in a storage plant

The hydraulic storage plants play a strategic role in the management of large electrical networks. Besides the widely known capability to store and provide great amount of energy, in a green and efficient way, these plants are of utmost importance to guarantee the perfect balance of the Italian electricity grid. For this reason the reversible turbomachineries, used in these plants, are subjected to a particularly intensive use which strongly affects their reliability. The present work deals with a real issue of the ENEL Green Power "Anapo" storage hydro plant, located in Sicily (Italy). In this plant strong and increasing vibrations were detected in the Fink's guide vane, particularly during the pumping operating conditions. In order to find the sources of these vibrations and for a quantitative evaluation of the structural loads on the Fink's guide vane blades, an unsteady CFD 3D model of the reversible turbine was implemented and validated using data provided by ENEL. The model accurately reproduced the hydrodynamic behavior of the water flow within the entire machinery, between the Kaplan's diffuser and the spiral case. This allowed for the calculation of the time dependent trend of the structural loads over the Fink's vane blades. The frequencies and the amplitudes of the loads were analyzed through the use of a Fast Fourier Transformation. Moreover, the CFD model allowed for a sensitivity study of the guide vane opening angle effects. This study provides an interesting insight into the hydrodynamic behavior of the machine.

Transient simulation on closure of wicket gates in a high-head Francis-type reversible turbine operating in pump mode

To solve the problem of grid instabilities, regulation in the Pumped Hydro Energy Storage (PHES) plants should quickly respond to the variation of electricity produced by unpredictable renewable energy. In this paper, a power reduction scenario applied to a pump turbine of a PHES is simulated considering the transient closure process of wicket gate. A novel dynamic mesh technique is applied to simulate the rotation of wicket gate vanes from best efficiency point to shutdown condition. Detached Eddy Simulation (DES) turbulence model is utilized to capture complex unsteady flow and the water weak compressibility effect is considered in the transient simulation. Flow rate, torque, power and pressure are analysed by the Fast Fourier Transform (FFT) and Continuous Wavelet Transform (CWT) methods. The results illustrate the delay between the performance parameters flow rate and power and the wicket gate opening angle. The closure of wicket gates affects the flow characteristics downstream the wicket gates greatly, causing intensive pressure fluctuations. The magnitude of pressure fluctuations downstream the wicket gate becomes the highest with the wicket gate closure of about 60%. Aside the blade passage frequency, a low frequency occurs, with the appearance of unsteady flow in pump turbine. Moreover, strong torque pulsations occur on the pin of the wicket vane when the percentage of closure is between 60% and 80%, with peaks much higher than that at the best efficiency point. The transient results can provide meaningful reference to the regulation law of wicket gate for safe operation of the pump turbine.

Study on the transient evolution law of internal flow field and dynamic stress of reactor coolant pump under rotor seizure accident

When the reactor coolant pump (RCP) operates under rated conditions, the rotor is suddenly forced to stop rotating in a very short time because of the great resistance moment. This nuclear accident is called rotor seizure accident and is the most extreme nuclear accident in a nuclear power plant. After the rotor seizure accident, the coolant flow rate of the primary circuit system drops sharply, the core temperature rises, and the fuel rod is forced in a danger of deviating from the bubble core boiling (DNB). In this paper, the AP1000 reactor coolant pump is taken as the research object, and the transient transition process under the rotor seizure condition are studied. Firstly, the simulation calculation of bidirectional fluid-structure coupling was verified by experiments. Then on the basis of considering the bidirectional fluid-solid coupling, the numerical simulation method is applied to study the flow law inside the reactor coolant pump and the deformation and stress distribution of the blade under the rotor seizure condition. The results show: the rotor seizure accident condition is a transient transition from a normal pump condition to a reverse turbine condition; when the rotor seizure accident occurs, the high specific pressure energy zone in the pump is gradually transferred from the volute to the inlet section; due to the direct impact of the liquid flow, the impeller is a concentrated area of high stress; high pivot dynamic stress was generated easily at the juncture between the inlet and outlet edges and the front and back cover plates of the impeller, which would transfer with the evolution of the rotor seizure accident.

Performance of fluidic diode for a twin unidirectional impulse turbine

The rectification-valve system has been invented to drive an air turbine equipped with the oscillating water column (OWC) based wave energy plant. However, this flow rectification system has widely regarded as impractical, except possibly in small devices like navigation buoys, due to the lack of durability of the valves and its complex mechanism. Moreover, as the valve size must be large for a high output, that makes the system practically infeasible. Therefore, a twin unidirectional impulse turbine topology has been suggested in previous studies to make the system valueless; the conventional unidirectional air turbines can be used. In this topology, the bidirectional airflow is rectified by the pressure difference between two unidirectional impulse turbines, and the most of airflow should get through the forward turbine. However, our previous study suggested that the mean efficiency of the twin turbine system would be lower than that of the unidirectional impulse turbine, since a portion of airflow gets through the reverse turbine whose efficiency is very low. In this study, a fluidic diode was adopted in the twin unidirectional impulse turbine system in order to reduce the air flow through the reverse turbine. The wind tunnel test and computational fluid dynamics (CFD) analysis were conducted to investigate the effect of fluidic diodes on the turbine performance. Further, the usefulness of a fluidic diode in the twin unidirectional impulse turbine topology to be discussed from the view point of mean efficiency under an unsteady flow condition.

Flow induced noise characterization of pump turbine in continuous and intermittent load rejection processes

In order to study pump turbine stability in view of flow induced noise, this paper focuses on two-part operation of one high head reversible turbine: transient load rejection process and intermittent vane closing conditions. Both above simulations are solved by DES turbulent model, additionally, the flow field results are regarded as sound source and analyzed comparatively by LMS software. Except for flow field interpretation, some developing rules of flow induced noise during the period of pump turbine load rejection are found. The result indicates that flow induced noise radiation is consistent with internal fluid characteristics, and the developing trends are similar which acquired from these two part calculations, whereas the values are distinct. This work provides a reference for the study of pump turbine operating stability from the acoustic aspect, and for pump turbine design work as well.

Numerical Study on the Internal Flow Field of a Reversible Turbine during Continuous Guide Vane Closing

The unsteady flow field in a reversible pump-turbine is investigated during the continuous load rejection using a 3D computational fluid dynamic analysis. Numerical calculations are carried out using the detached eddy simulation (DES) turbulence model and a new approach involving automatic mesh motion. In this way, the instability of the flow field is analyzed by continuously changing the guide vane openings from the best efficiency point (BEP). Unsteady flow characteristics are described by post-processing signals for several monitoring points including mass flow, torque, head and pressure in the frequency and time-frequency domains. The formation of vortices of different scales is observed from the origin to further enlargement and stabilization; the effect of the rotating structures on the flow passage is analyzed, and the influence of unsteady flow development on the performance of the turbine is investigated. Finally, the evolution during the period of load rejection is characterized in order to determine the hydrodynamic conditions causing the vibrations in the machine.

Off-stream Pumped Storage Hydropower plant to increase renewable energy penetration in Santiago Island, Cape Verde

In order to reduce the high dependence on imported fuels and to meet the ongoing growth of electricity demand, Cape Verde government set the goal to increase renewable energy penetration in Santiago Island until 2020. To help maximize renewable energy penetration, an off-stream Pumped Storage Hydropower (PSH) plant will be installed in Santiago, in one of the following locations: Chã Gonçalves, Mato Sancho and Ribeira dos Picos. This paper summarizes the studies carried out to find the optimal location and connection point of the PSH plant in Santiago’s electricity network. This goal was achieved by assessing the impact of the PSH plant, in each location, on power system stability. The simulation tool PSS/E of Siemens was used to study the steady-state and dynamic behavior of the future (2020) Santiago MV grid. Different scenarios of demand and renewable resources were created. Each hydro unit of the PSH plant was modeled as an adjustable speed reversible turbine employing a DFIM. The results show that Santiago’s grid with the PSH plant in Chã Gonçalves is the one that has the best performance.

CONTRIBUCIÓN DE UNA CENTRAL REVERSIBLE CON BOMBEO A VELOCIDAD VARIABLE A LA REGULACIÓN FRECUENCIA-POTENCIA DE UN SISTEMA AISLADO

The development of renewable energies is growing in recent years, promoted by many governments in response to climate change. The main drawbacks of renewable energies, come from uncertainty and variability in the short term of wind and solar radiation. For many years, pumped storage power plants have become one of the most important means to cover the lack of regulation, characteristic of aforementioned renewable energies. In addition, pumped storage power plants can nowadays be operated with variable speed, thanks to last decades improvements in electronic frequency converters. Converters are usually limited by electrical magnitudes (voltages or currents) but in some cases hydraulic limits can be more restrictive, as in high head power plants. The main objective of this work is to study the influence of a pumped storage power plant with variable speed on an isolated system, and to analyze how the hydraulic limits of the reversible turbine in pumping mode reduces the power plant regulation capacity. For this purpose, a dynamic model of the power plant and the isolated system has been developed by means of Matlab/Simulink. Some simulations are carried out and it is indeed stated that hydraulic characteristics constrain the possibility of the pumped storage power plant, to offer load-frequency regulation in the secondary market. Keywords: Pumped storage power plant, variable speed, load-frequency control, hydraulic stability limit, long penstock, simulation model

Structure and fluid optimization of the guide vane blade with the decomposition of the optimization problem

The paper presents a new method for the fully automated decomposition of the optimization problem. The decomposition is performed on the space of the optimization input arguments. The method is firstly tested on the optimization of the mathematical functions. Afterwards, the decomposition method is used to optimize the geometry of a guide vane blade of a reversible water turbine. The objectives of the optimization are the maximal efficiency of the whole turbine and the minimal volume of a single blade with the condition that the blade remains undamaged during the normal operation of the turbine. The fluid analysis is performed with the use of the finite volume method, while the structural analysis is performed either with the finite element method or with the meshless method. The comparison of the two structural analysis methods shows that they have a different result sensitivity about the mesh distortion. A comparison of optima, obtained on the basis of both structural analysis methods, is made in order to assess the impact of the mesh distortion on results of the design optimization.

CFX Modeling of an Axial Turbine with Symmetrical Blades and Reversible Flow for Tidal Power Plants

From studies of a reversible flow turbine for using in tidal power plants it was obtained a model with symmetrical blades that shows this characteristic. For the obtaining of more accurate results of this type of turbine it was proposed the manufacturing of a physical sample to be used in a testing bench at the Hydromechanical Laboratory of Small Hydropower Plants LHPCH, at Centro Nacional de Referências de PCH, (National Centre of Reference in SHP) CERPCH, in Universidade Federal de Itajubá (Federal University ofItajubá) UNIFEI, and also a mathematic sample modeled on CFD/CFX platform with the ANSYS software. This paper aims to describe one of the tests of the proposed rotor on mathematic model, to be used tidal power plants turbines.

Exergetic Destruction Effects of Operating Conditions on the Turbojet Engine Components

The minimization of exergy destruction brings the design as closely as permissible to the theoretical limit. This study presents exergy destruction analysis of a turbojet engine for different flight Mach number and altitudes. Turbojet engine being considered consists of an inlet, a centrifugal compressor, reverse flow combustion chamber, axial-flow turbine and exhaust nozzle. The flight Mach number and altitude are examined on the exergetic destructions of compressor, combustion chamber, turbine and exhaust nozzle. The results of component-based destruction analysis are given as three dimensional exergetic-destruction response surface plots related to altitude and flight Mach number.

Exergetic and Energetic Response Surfaces for Small Turbojet Engine

Exergy analysis permits meaningful efficiencies to be evaluated for a system or process, and the sources, causes and locations of thermodynamic losses to be determined. This study presents exergetic modeling of a small turbojet engine via exergetic response surfaces. Turbojet engine consists of an inlet, a centrifugal compressor, reverse flow combustion chamber, axial-flow turbine and exhaust nozzle. The flight Mach number and altitude are examined on the exergetic efficiencies of total engine performance. The results of analysis are given as three dimensional exergetic response surface plots related to these operating parameters.

Accuracy details in realistic CFD modeling of an industrial centrifugal pump in direct and reverse modes

Numerical computation of the flowfield inside a pump is herein used as a numerical laboratory, subject to the limitations of modeling assumptions and to experimental verification. A numerical computation of the flow inside a real industrial centrifugal pump is performed that includes a very sophisticated geometry. Conversely to other computations, in this test case no simplification of the geometry was introduced. Numerical computations are obtained using Spalart-Allmaras turbulence model. A detailed analysis of the turbulent flowstructure is performed for the design point and two off design conditions. Additional computations were performed in order to compare the numerical and experimental pump characteristics; these were obtained under normalized testing conditions. Further computations are presented for the pump working in reverse turbine mode (PAT). Detailed analyses of the flow allow a comparison of the internal flow losses when the pump is operating in direct and reverse mode. This is also useful to help in the selection of an adequate pump geometry that can work in both modes with best efficiency.

Fatigue cracks and failures in cement industry, shipbuilding and power plant facilities

In spite of numerous and expensive researches in the field of fatigue, cracks and failures caused by fatigue occur every day in all fields of human activity. The paper presents some typical fatigue damages in industry and transport. Fatigue failure of the main engine lateral support (at the bulk carrier), fatigue cracks at the large portal crane, fatigue cracks together with failures in the large gear wheel of cement mill, and fatigue failure of the reversible turbine rotor, are described herein. The complete damage analysis (numerical and/or experimental stress distribution evaluation, fractography, assessment of remaining service life, etc.) showed that design errors have caused all of these, and many other cracks and failures. The analysis confirmed the possibility of crack and failure repairs, what has been done successfully.

Totally implantable intrathoracic ventricular assist device

A totally implantable, intrathoracic electrohydraulic ventricular assist device (EVAD) is being developed for permanent use or as a bridge to transplantation. The blood pump with 70-mL nominal stroke volume, volume displacement chamber, reversible turbine, internal electronics and infrared diaphragm position sensor are combined in one compact unit (unified system). The size and geometry are based on human anatomic measurements and fluid dynamic studies. A transcutaneous energy transfer powers the system and recharges the implantable nickel-cadmium battery pack. Autotuning circuitry optimizes energy transfer efficiency over a range of transcutaneous energy transfer coil spacings and misalignments. An infrared diaphragm position sensor detects end-systole and diastole points. In vitro and acute in vivo tests have demonstrated flow rates greater than 6 L/min. The transcutaneous energy transfer system demonstrated power transfer efficiencies of 60% to 80% for power demands from 5 to 60 W. Thirteen systems are currently undergoing durability testing; one has run for more than 750 days failure-free. The system recently sustained circulation in an acute calf implantation for 96 hours. Results of the in vitro and in vivo testing to date have demonstrated that the developed system can function effectively as a totally implantable ventricular assist device. Chronic in vivo evaluation is planned.

Investigation of transient phenomena on a model of a reversible turbine at the Kiev pumped-storage plant

1. One of the causes of periodically varying disturbing forces in the blading of a pump-turbine during its operation as a pump is the peripheral nonuniformity of the flow at the runner outlet due to hydrodynamic wakes from the blades. 2. The dynamic moments on the guide apparatus vanes of a reversible machine in the turbine regime are apparently the result of the opposite effect of the rotating blade system on the fixed cascade of the guide apparatus located at a distance of (0.05–0.16)t, where t is the cascade pitch from the edges of the runner blades. 3. Investigations showed the need to take into account the alternating dynamic moments acting on the vanes in the pump and turbine regimes when designing the guide apparatus of a reversible machine. 4. Pressure fluctuations in the pump regime have a tendency to increase slightly with decrease of the anticavitation margin, which is not observed in the turbine regime.

HORMONE STUDIES WITH THE ULTRACENTRIFUGE

1. An ultracentrifuge is described in which the rotor is driven by a compressed air turbine, and is spun in an evacuated chamber to minimize friction and heating. The rotating parts are supported by a cushion of air in an air bearing. 2. The centrifuge rotor holds 10 test tubes inclined at 45 degrees to the axis, and has a capacity of 55 cc. It is operated at a maximum speed of 51,000 R.P.M., which develops at the top of the fluid column in the test tubes a centrifugal field of over 100,000 times gravity, and at the bottom of the fluid column a field of over 200,000 times gravity. 3. By means of a reverse turbine, the rotor can be brought to a stop from full speed in a relatively short time. 4. A precession damping device is described, which effectively damps the precession and wobbling of the rotor that usually occurs at certain speeds in machines of this type. 5. A relatively long section of shaft is used between the centrifuge rotor and lower bearings. This prevents vibrations from being appreciably transmitted through the shaft to the lower bearings and driving mechanism, and results in a negligible wear on the bearings. 6. The driving mechanism is designed so that the positions of its parts are adjustable, and so that the driving mechanism may be dismantled without disturbing these adjustments.