Runner Chamber Research Articles

Hydro-abrasive erosion in Kaplan turbines: a case study

ABSTRACT Sediment in the flowing water causes hydro-abrasive erosion of hydraulic turbines and other underwater components. In the present study, erosion quantification in the Kaplan turbine of a low-head hydropower plant (HPP) on the Upper Ganga Canal, is considered in the study. The study uses the guidelines of the International Electrotechnical Commission IEC 62364: 2019 for quantifying erosion in the Kaplan turbine. This work extends the research of Rai and Kumar (2016) and uses their primary details of some suspended sediment and operating parameters. The shape and mineral composition of the suspended sediment were quantified using dynamic imaging and X-ray diffraction techniques, respectively. The annual average particle load at the study HPP is obtained to be 356.87 kg·h/m3. Based on the analysis, it is estimated that the erosion depth varies from 0.88 to 1.37 mm/year at the blade tip, whereas from 2.40 to 3.74 mm/year at the blade outlet. At the runner chamber, the erosion depth varies from 1.27 to 1.98 mm/year. The erosion depth varies from 0.01 to 1.53 mm/year in the guide vanes. The calibration factor corresponding to the maximum erosion in guide vanes is estimated to be 1.75 × 10−5.

Numerical Study on Valve Closing Criteria during Pump-turbine Start-up on Pump Mode

Abstract Vibrations of exhaust pipes have been observed in some hydropower stations during the exhaust process of pump-turbine start-up on pump mode due to water ingress into the pipes. It may have a safety risk for the pump-turbine start-up process when exhaust pipes are operating under the compressed air-water two phase flow. Since the numerical simulation researches about pump start-up process have been rarely reported and the development of flow field in exhaust pipe is lack of quantitative cognition, it calls for an urgent need to supplement related works. In this paper, the transient full-channel two-phase numerical simulation research on the pump mode return water exhaust process of a pumped power station is carried out by Reynolds-Averaged Navier-Stokes approach. This work put emphasis on the characteristics of cone water level, runner torque and air speed in exhaust pipes after the compressed air released from the runner chamber. Then development laws and relationship with the exhaust valve closing timing are analysed and concluded. Results show that the cone water level, runner torque and air speed pulsation signal of exhaust pipes can be used as exhaust valve closing criteria, and the third criterion has the largest time margin.

Cavitation identification in a hydraulic bulb turbine based on vibration and pressure fluctuation measurements

Cavitation can lead to reduced efficiency, increased vibration and noise in hydraulic turbines. Accurate and rapid identification of cavitation states in a turbine is important. In this work, a test system has been constructed for a hydraulic bulb turbine, to synchronously obtain cavitation images on runner blades, vibrations on both the runner hub and the runner chamber, and pressure fluctuations on the draft tube of the turbine at different cavitation conditions. The multifractal characteristics of the collected signals obtained by using the multifractal detrended fluctuation analysis method have been analysed and compared in detail. It is found that the multifractal characteristics of the vibrations and pressure fluctuations depend strongly on the cavitation state. The multifractal strength of the pressure fluctuations in the draft tube is stronger than that of the vibrations on the runner, induced by cavitation. Furthermore, some multifractal parameters of vibrations and pressure fluctuations have been extracted and used for cavitation state identification in the turbine, which is important for safe operation of a turbine.

Study on the Cavitation Characteristics of Shroud Clearance in Prototype and Model of a Kaplan Turbine

Model tests and model calculations are the most basic means currently available to study the characteristics of the axial-flow pumps and Kaplan turbines in a systematic manner. Large and medium-sized turbine units and axial-flow pumps must rely on model tests and model calculations to ensure the performances of prototype units before designing. The conversions between models and prototypes are mainly carried out through similarity criteria. However, it is difficult to meet all the similarity criteria in the model tests and the similarity conversions, and the hydraulic and cavitation performances of the model and the prototype are often different. In this paper, numerical calculations of shroud clearance cavitation are performed on both the prototype and model using different cavitation coefficients. The results indicate that the prototype and model have a similar clearance cavitation flow regularity when the cavitation coefficient changes, but they have different energy characteristics and cavitation characteristics. In cavitation conditions, the prototype has higher energy characteristics than the model and the critical cavitation coefficient is similar to the model. When the cavitation coefficient is higher than the critical cavitation coefficient, compared to the model, the blade cavitation performance of the prototype is worse, and the clearance cavitation and runner chamber cavitation are more serious. If the cavitation coefficient decreases to the device cavitation coefficient, the runner chamber of the prototype will cavitate, even though the model has not cavitated yet. The comparison of shroud clearance cavitation between the prototype and the model can be used as a reference for the accuracy of similarity conversion results between the model and the prototype. It also has a positive impact on the design and operation of the prototype.

Simulation analysis of energy characteristics of flow field in the transition process of pump condition outage of pump-turbine

The pump-turbine is the heart of a pumped storage power plant. This study combines numerical simulations with experiments to investigate the flow stability, energy loss in the main flow area and their interconnection in the transition process of the double-row cascade and runner chamber of the pump-turbine, when the pump-turbine is operated under pumping conditions with a sudden power failure and the guide vane refuses to close. The results show that the overall flow pattern of the transition process is extremely unstable, and the flow state is presented as smooth-disturbed-smooth-disturbed, with the maximum vorticity difference(Δω) of 696756 s−1 in the neighboring working conditions; the maximum entropy production rate of the double-row cascade and runner chamber in the braking process has a similar trend in the vorticity change trend, and the rapid change of the flow pattern of the internal fluid causes the sharp change of the entropy production in the pump-turbine; The maximum entropy production rate in the runner chamber is of the order of e6, which is much higher than that in the other regions, and the poor flow phenomenon caused by the runner is the main reason for the energy loss.

Vibration Characteristics of a Tubular Turbine Prototype at Different Heads with Considering Free Surface and Water Gravity

Tubular turbines are widely used in low water head and tidal power development due to their straight flow path, simple structure, and wide efficient area. However, the severe vibration during actual operation greatly affects the safe operation of the tubular turbine. This study performs a numerical calculation of the tubular turbine, which meets the actual machine conditions considering the free surface and water gravity; compares and analyzes the flow characteristics and pressure fluctuation spectrum characteristics in the tubular turbine under different water heads; and verifies the comparison with the actual machine test results to explore the vibration characteristics and vibration mechanism of the tubular turbine. Research results show that a large pressure difference is observed between the top and bottom of the runner chamber, and the runner needs to experience large periodic pressure fluctuations during rotation due to the combined effect of hydrostatic pressure and hydrodynamic pressure. Under different water heads, obvious flow turbulence and high turbulent kinetic energy areas are observed in the runner and draft tube due to the influence of the shape of the blade wake vortex. The vibration in the tubular turbine is mainly concentrated in the runner and draft tube and influenced by the water gravity and the runner structure of the transverse cantilever beam. The amplitude of pressure fluctuation is the largest when the frequency inside the runner is the blade passing frequency at each water head, so the maximum vibration position is located at the runner. The research results serve as a guide for the design and operation of the horizontal tubular turbine.

Numerical Simulation of Flow-Induced Noise in Horizontal Axial Flow Pumps in Forward and Reverse Conditions

This paper investigates the influence of pressure pulsation and flow-induced noise using a two-way dual-purpose pump. The pressure pulsation signal is obtained from the Detached Eddy Simulation (DES) turbulent model calculation as the fan sound source, and the noise sound field distribution in the impeller is calculated. The numerical results show that the external characteristics and pressure pulsation obtained from the simulation correlate well with the experimental values. Under different working conditions, the pressure pulsation decreases with the increase in the flow rate; no evident dominant frequency occurs in the frequency spectrum at a low flow rate, and many spurious frequencies occur. The primary frequency in the runner chamber is the leaf frequency, and that in the nonblade area is the rotating frequency. The sound field distribution of the flow-induced noise has dipole characteristics, and its directivity distribution and sound pressure radiation level can reflect the pressure pulsation characteristics. It is primarily affected by the blade frequency, and the distribution with the flow rate is consistent with the pressure pulsation. Avoiding a low flow and operating in a reasonable flow area can effectively reduce pressure pulsation and flow-induced noise and ensure the stability of unit operation.

Test and Numerical Simulation of Pressure Pulsation under the Forward and Reverse Working Conditions of a Horizontal Axial Flow Pump

In daily operation, the flow state in the runner chamber of an axial flow pump is extremely complex, and the pressure pulsation caused by the vibration of the unit and the hydraulic excitation is also extremely complex. The pressure pulsation will also greatly damage the flow components of the unit. In this paper, a pressure pulsation test and research on an axial flow pump in a pumping station are conducted. The research results indicate that the pressure pulsation at the inlet of the runner and the inlet of the front guide vane are basically consistent with the numerical simulation results under the rated operating conditions, and the external characteristic curves are basically consistent. When running in the forward direction, the pressure pulsation at the inlet of the runner periodically changes, and the main frequency is the rotational frequency. In the reverse operation, the main frequency of the pressure pulsation at the outlet of the runner is the rotational frequency, and the main frequency of the pressure pulsation at the outlet of the movable guide vane is the pilot frequency; the pressure coefficient changes under different flow conditions. The distribution trends are consistent and decrease with the increase in flow rate; the velocity streamlines are evenly distributed near the design flow rate but are sparse and uneven under low flow conditions. Deviation from the design flow rate should be avoided during normal operation of the unit conditions to ensure safe and stable operation.

Research and Application of Neutron Detection Technology in Inspection of Void Defects in Turbine Runner Chamber

After a long-term operation of the turbine runner chamber, there may be voids between the steel lining and the concrete. If it is not discovered and treated in time, the safe and stable operation of the unit will be affected. In engineering practice, the hammering method is often used to detect hole defects, and the accuracy is low. The neutron detection technology is proposed to detect the void defects of the steel lining, quantitatively display the void location and size, and improve the accuracy of void defect detection.

Numerical Prediction of Runaway Characteristics of Kaplan Turbines Applying Cavitation Model

In case of disconnection of generator from the network and failure of the governor, the rotational speed of the rotor rapidly increases and achieves maximum value, called the runaway speed. This value depends on the turbine type, the operating condition, the turbine flow passage and the runner geometry, and for Kaplan turbines might 2.5 times surpass the nominal rotational speed of the runner. The runaway speed is important for evaluation of mechanical resistance of the generator rotor. The value of runaway speed is determined based on the results of the model tests upon completion of the design works related to the runner. Therefore, accurate computation of the runaway speed will improve the design process for the runner and the whole turbine unit. Given in this paper is the numerical computation of the runaway speed for a Kaplan turbine of 40 m head. Calculations were carried out for a series of steady-state operating conditions with different runner speeds and the speed at which the torque on the runner shaft is equal to zero was determined. Two approaches for numerical simulation were compared. In the first one, the flow in the turbine was simulated using 3-D RANS equations of incompressible fluid using k-ε model of the turbulence. In the second approach, cavitation phenomena were taken into account using two-phase Zwart-Gerber-Belamri (ZGB) cavitation model. Steady-state computations were carried out in computational domain that included one guide vane channel, one runner channel, the whole draft tube, and the clearances between the runner blade and the hub as well as between the blade and the runner chamber. When setting the boundary conditions, the turbine head, being the difference of energies in the inlet and outlet cross-sections, is pre-set as a constant value, while the discharge and the runner torque are determined in the process of computation. The computed runaway speed is compared to that obtained in the model tests. It is shown that the numerical prediction of the runaway speed using the cavitation model achieves better matching with the experimental data.

Research on tip clearance leakage flow field characteristics of tidal energy hydroelectric unit based on NACA0009 hydrofoil

In the rotor passage of tidal energy hydroelectric unit, there is a tip leakage problem between rotor and runner chamber. In order to research the flow characteristics of tidal energy hydroelectric units and explore the control method of tip leakage, based on the experimental data of NACA0009 hydrofoil, the SST-CC turbulence model was used for numerical simulation and compared with the experimental results. The characteristics of tip leakage flow and vortex were analysed under different hydrofoil shapes and gap widths. The results show that the rounded hydrofoil can effectively control the generation of tip separation vortex, but the rectangular hydrofoil has higher vortices coefficient and lower pressure coefficient in the downstream section; the tip leakage amount will increase with the increase of gap width; the tip vortex intensity will increase first and then decrease, and cavitation may occur when the vortices is maximum. The results can provide reference for studying the control method of tidal energy hydraulic machinery clearance leakage.

Application test of a Detection Method for the Enclosed Turbine Runner Chamber

At present, for the existing problems of the testing methods for the key hidden metal components of the turbine runner chamber, such as the poor reliability, the inaccurate locating and the larger detection blind spots of the detection device, under the downtime without opening the cover of the hydropower turbine runner chamber, an automatic detection method based on real-time image acquisition and simulation comparison techniques was proposed. By using the permanent magnet wheel, the magnetic crawler which carry the real-time image acquisition device, could complete the crawling work on the inner surface of the enclosed chamber. Then the image acquisition device completed the real-time collection of the scene image of the enclosed chamber. According to the obtained location by using the positioning auxiliary device, the position of the real-time detection image in a virtual 3D model was calibrated. Through comparing of the real-time detection images and the computer simulation images, the defects or foreign matter fall into could be accurately positioning, so as to repair and clean up conveniently.

Analyzing hydro abrasive erosion in Kaplan turbine: A case study from India

Sediment flow through hydro turbine causes erosion of hydraulic components resulting in drop of turbine efficiency, particularly in hydropower plants of the Himalayan region. The measurement of erosion and monitoring of sediment flow in turbine are major concerns in erosion study. Attempts have been made to study erosion mainly in Pelton and Francis turbines. In this study, a simple and effective method has been presented to measure erosion in a Kaplan turbine of a run-of-river scheme Chilla hydropower plant in foothills of Himalaya. Recent techniques were used to measure sediment parameters like concentration, size, shape and mineral content. A standard erosion model is applied to estimate the erosion in Kaplan turbine blade, runner chamber and draft tube cone. A calibration factor has been proposed to apply the erosion model for site specific conditions. It has been found that the outer trailing edges of the turbine blade and upper runner chamber are most erosion prone zones. Sediment analysis revealed that effective operation can reduce erosion in turbine components. The estimated erosion values from model are found to be consistent with measured values. Finally, suggestions for design improvements and effective operation of erosion affected hydropower plants are given.

Effect of Air Layer on the Performance of an Open Ducted Cross Flow Turbine

Recently, the cross flow turbines attract more attention for their good performance over a large operating regime at off design point. This study employs a very low head cross flow turbine, which has open inlet duct and has barely been studied before, to investigate the performance of the cross flow turbine with air suction from the rear part of the runner. Unlike conventional cross flow turbines, a draft tube is attached to the outlet of runner to improve the turbine performance. Water level and pressure in the draft tube are monitored to investigate the influence of air suction. Torque at local blade passage of three parts of runner is examined in detail under the conditions of different air suction. Consequently, it is found that with proper air suction in the runner chamber, the water level in the draft tube gradually drops to Stage 2 of the runner and the efficiency of the turbine can be raised by 10%. Overall, the effect of air-layer on the performance of the turbine is considerable.

Modal Analysis on a Runner Chamber for a Large Hydraulic Bulb Tubular Turbine

The vibration was severe for a runner chamber of a large hydraulic bulb tubular turbine, which caused some cracks. The PRO/E software was adopted to establish a 3D model of the runner chamber. Based on ANSYS Workbench V14.5, a modal analysis was done. Its natural frequencies and modal shapes were obtained. The influence on modal characteristics with the runner chamber’s structure was discussed. The study shows that the reinforce stiffener’s thickness, the circumferential endlessband and their thicknesses have few effect on the modal characteristics of the runner chamber, the latticed reinforce stiffener has more effect on the modal characteristics. These results will provide the basis for product optimum design, so that its natural frequencies stagger these frequencies of field vibration, the resonance and the crack do not occur in the runner chamber.

Internal Flow Analysis on an Open Ducted Cross Flow Turbine with Very Low Head

Recently, the cross flow turbine attracts more and more attention for its good performance over a large operating regime at off design point. This study adopts a very low head cross flow turbine that has barely been studied before, and investigates the effect of air layer on the performance of the cross flow turbine. As open duct is applied in this study and free surface model is used between the air layer and water, an engineering definition of efficiency, instead of traditional definition of efficiency, is used. As torque at the runner fluctuates up and down at a reasonable limit, statistical method is used. Pressure and water volume fraction contours are shown to present the characteristics of air-water flow. With constant air suction in the runner chamber, the water level gradually drops below the runner and efficiency of the turbine can be raised by 10 percent. All considered, the effect of air layer on the performance of turbine is considerable.

Vibration Frequency Spectrum Measurement on a Hydraulic Turbine Runner Chamber for a Large Bulb Hydraulic Generator Set

The vibration is severe for a hydraulic turbine runner chamber of a large bulb hydraulic generator set. A measurement and analysis system is composed of an acceleration transducer, a charge amplifier, and a dynamic data collecting & analyzing system. It is used to test the frequency spectrum, which provide a basis for the optimization design based on the modal analysis, so that its natural frequencies can stagger these frequencies of vibration sources, the resonance does not occur and the vibration is reduced.

Hydraulic performance improvement of the bidirectional pit pump installation based on CFD

At present, the efficiency of bidirectional pit pump installation with lift under 2m is still low because of lack of research on it in the past. In the paper, the CFD numerical method and experimental test were applied to study flow characteristic of bidirectional pit pump installation under positive and reverse condition. Through changing airfoil type and position of blade and stay vane, the comprehensive performance of improved model were obtained by calculating many different models. The results showed that when improved model is obtained with type A runner with 4 blades that is 0.7D away from pit exit and unsymmetrical guide vane 0.25dh which away from the impeller outlet, and the flow pattern of the improved solution is steady with high efficiency. Compared with the original scheme, the efficiency of positive and reverse design condition reach to 67.23% and 58.32% respectively, which is increased 6% more than original model on the design condition and 5% on the optimum operating condition, and it achieved the purpose of improvement. According to the runner blade angle of the optimization solution, model synthetic characteristic curve was drawn and internal flow field characteristics was analyzed under optimal positive and reverse conditions. The numerical calculation shows that owing to the lack of stay vane to recycle the energy in outlet runner chamber, the water flow regime is not steady enough in the outlet passage, and that is the main reason for lower efficiency at reverse condition than that at positive condition.

Electrical braking of synchronous generators for combined generator and water turbine bearings as well as stray‐load losses determination

This study describes a new method for determining combined synchronous generator and water turbine bearings losses as well as stray-load losses of a generator, based on measurement of the speed change during electrical braking. In the electrical braking regime, the total braking torque of a hydrogenerator is made up of the torques defined by losses in the runner chamber of the hydraulic turbine, ventilation losses in the hydraulic-turbine generator, bearings losses in the generator and the water turbine, as well as electromagnetic and stray-load losses in the short-circuit. In this study, the torque–speed curve is represented by the corresponding equations which describe all the torques occurring during electrical braking. By applying these equations to the measured results and using some numerical calculations, combined generator and water turbine bearings losses as well as stray-load losses can be obtained. The proposed method is applied on a 190 MW generator at the Hydro Power Plant (HPP) Djerdap (in Serbia). The obtained results demonstrated a very high level of accuracy when compared with the values found in the manufacturer's technical documentation (Electrosila). The proposed method has the best and most economical use in large synchronous generators and generators in older power plants.

Kaplan turbine tip vortex cavitation – analysis and prevention

The work is focused on one type of Kaplan turbine runner cavitation – a tip vortex cavitation. For detailed description of the tip vortex, the CFD analysis is used. On the basis of this analysis it is possible to estimate the intensity of cavitating vortex core, danger of possible blade surface and runner chamber cavitation pitting. In the paper, the ways how to avoid the pitting effect of the tip vortex are described. In order to prevent the blade surface against pitting, the following possibilities as the change of geometry of the runner blade, dimension of tip clearance and finally the installation of the anti-cavitation lips are discussed. The knowledge of the shape and intensity of the tip vortex helps to design the anti-cavitation lips more sophistically. After all, the results of the model tests of the Kaplan runner with or without anti-cavitation lips and the results of the CFD analysis are compared.