Hydraulic Turbine Research Articles

Investigations of Spoilers to Mitigate Columnar Vortices in Propeller Turbines at Speed-No-Load Based On Steady and Unsteady Flow Simulations

Abstract With the introduction of an ever-larger share of renewable but intermittent energy sources on electrical grids, hydraulic turbines are more often used as network stabilizers. In such a role, they are generally operated in off-design operations like speed-no-load (SNL). No energy is extracted from the flow at SNL operation, but the runner rotates at the synchronous speed linked to the electrical grid. The flow inside the runner of low-head turbines operating at SNL is often dominated by a columnar vortex array that may induce damaging pressure fluctuations. This paper presents the study of a control device to mitigate those vortices. At SNL, the small guide vane opening leads to a high swirl in the runner generating secondary flows such as columnar vortices and backflows. The proposed concept is to move SNL operation toward a higher guide vane opening and hence lower swirl, preventing the formation of a columnar vortex array. Lowering the input swirl of SNL is accomplished by opening up the guide vanes while using a control device to limit the discharge. The control device, like a spoiler on an aircraft wing, is introduced on the guide vanes to generate added head losses, significantly decreasing the discharge. This paper compares the hydrodynamics of the flow in a propeller turbine with different spoiler geometries. The study is based on both RANS and URANS flow simulations. It highlights how such devices can successfully mitigate columnar vortices and their associated pressure fluctuations on runner blades.

Generation of Electricity From a Hydraulic Turbine in the Djonou River (Benin)

The shortage of electricity in rural areas despite the hydraulic potential they possess is becoming a challenge for Benin. To date, nearly 140,000 people spread over the 42 lakeside villages of this country live in energy inaccessibility, insecurity and poverty. To overcome this situation, the present study is therefore interested in the production of electrical energy on an experimental basis in low water periods thanks to an Archimedean screw turbine which operates at low flow rates and height of fall on the river. Djonou located in southern Benin a few kilometers from the University of Abomey-Calavi. The geometrical and hydraulic parameters of the screw were therefore determined and the device was modeled using Autocard software. A prototype was then made with local recycled materials and tested on the river. The screw specifications indicate an inside and outside radius of 0.072 m and 0.135 m. The length of the screw was set at 0.46 m for a blade radius estimated at 0.137 m. The number of screw blades is equal to 2 with a flow rate of 0.049 $ m^{3}/s $. The inclination angle of the screw is $25^{\circ}$. The device on the experimental site produces a voltage of 16 V and provides a current of about 0.12 A which can power a 2 W lamp. This performance of the prototype made on a small scale is a reliable indicator of the optimal use of this technology in the national hydraulic network of Benin to supply populations with electrical energy.

A Hybrid Algorithm Based on Social Engineering and Artificial Neural Network for Fault Warning Detection in Hydraulic Turbines

Hydraulic turbines constitute an essential component within the hydroelectric power generation industry, contributing to renewable energy production with minimal environmental pollution. Maintaining stable turbine operation presents a considerable challenge, which necessitates effective fault diagnosis and warning systems. Timely and efficient fault w arnings are particularly vital, as they enable personnel to address emerging issues promptly. Although backpropagation (BP) networks are frequently employed in fault warning systems, they exhibit several limitations, such as susceptibility to local optima. To mitigate this issue, this paper introduces an improved social engineering optimizer (ISEO) method aimed at optimizing BP networks for developing a hydraulic turbine warning system. Experimental results reveal that the ISEO-BP-based approach offers a highly effective fault warning system, as evidenced by superior performance metrics when compared to alternative methods.

Numerical Analysis of the Flow by Using a Free Runner Downstream the Francis Turbine

The current requirements of industrialized countries require the use of as much renewable energy as possible. One significant problem with renewable energy is that the produced power fluctuates. Currently, the only method available for energy compensation in the shortest time is given by hydroelectric power plants. Instead, hydroelectric power plants (especially the plants equipped with hydraulic turbines with fixed blades) are designed to operate in the vicinity of the optimal operating point with a maximum ±10% deviation. The energy market requires that hydraulic turbines operate in an increasingly wide area between −35% to 20% from the optimum operating point. Operation of hydraulic turbines far from the optimum operating point involves the appearance downstream of the turbine of a decelerated swirling flow with hydraulic instabilities (known in the literature as the vortex rope). The main purpose of this paper is to investigate numerically a new concept by using a free runner downstream on the main hydraulic runner turbine more precisely in the draft tube cone. The free runner concept requires rotations at the runaway speed with vanishing mechanical torque. The main purpose is to redistribute the total pressure and the moment between the shaft and the periphery. In addition, the free runner does not modify the operating point of the main hydraulic turbine runner.

Research on control system for improving the grid-connected efficiency of small hydropower

Aiming at the problem of low efficiency at low flow in small hydropower stations, a permanent magnet direct-drive hydropower generation control system based on dual PWM converters is proposed to realize wide-range variable-speed constant-frequency hydropower generation of hydraulic turbine units and improve the comprehensive power generation efficiency of small hydropower stations. In this control system, the hydraulic turbine is coaxially connected to the permanent magnet synchronous generator(PMSG) through the flywheel, and the power grid is connected by back-to-back dual PWM converters, and the bidirectional energy flow is realized by the voltage space vector pulse width modulation method. The generator-side converter controls the rotating speed of hydraulic turbine units and tracks the optimal speed point of the hydraulic turbine units in real time to realize the maximum power output of hydraulic turbine units. The grid-side converter adopts active power and reactive power decomposition control method to stabilize the DC bus voltage and provide the reactive power required by the grid. Finally, the effectiveness of the proposed control system was proved by comparative experiments in a 400V/200kW/428rpm small hydropower station.

Modal decomposition of flow instabilities in a straight turbine diffuser around the best efficiency point

Hydraulic turbines sometimes exhibit a sharp efficiency drop around the best efficiency point. The drop is known to originate from large flow separations in their draft tubes, limiting their ability to recover part of the residual kinetic energy exiting the runner. While the conditions leading to the onset of these separations are not yet understood, the potentially unstable vorticity distribution at the runner exit led to the hypothesis that those separations are the result of an interaction between the flow at the center of the draft tube and the boundary layer at the walls. To study this hypothesis, the turbulent flow inside the draft tube of a bulb turbine was measured with time-resolved particle-image velocimetry (TR-PIV). In this work, coherent structures are identified from spectral proper orthogonal decomposition (SPOD) of the velocity fields to correlate changes in their topology with the efficiency drop. Special attention is given to the periodic vortical motions in the runner's wake, whose shape and energy content are found to be linked to the flow rate. Three-dimensional reconstructions of the underlying structure reveal a shift in its topology that correlates with the efficiency drop and separations at the wall. In addition, comparisons of the SPOD coefficients with the runner position show that the phase angle between the structure and the runner remains the same for each operating condition, suggesting a link with a rotating flow imbalance in the runner blade channels.

Historical Background of the Origin of the Speeddroop, Additional Control Signals and Analogic Retrofit of a Governor of a Francis Turbine, Using Operational Amplifier IC741

It is well known that governors of turbines, moving synchronous machines are responsible to maintain the rotation of the rotor of the generator constant and then the electric frequency constant, independently of the changes of electric loads connected to the power electric net. This paper treats about the origin and necessity of the permanent and transitory speedoops in the control mash of a governor. First, we develop the historical background origin of a governor. The basic controls actions are studied, and the analogic circuits related, using operational amplifiers. Then, as an easier way, the author uses an analogic generic PID governor to explain how the permanent speedroop is needed to set the power delivered by a hydraulic turbine (Francis) and then the transitory speedroop. Additional control signal as Power Joint Control and Automatic Generation Control-AGC are introduced. As a suggestion, a simple analogic Power Joint Control circuit example, using operational amplifier 741 is given, but not tested in a workbench. The using of the Automatic Control Generation-AGC, a supplementary control, is introduced because of the necessity to correct the frequency deviations. It is also given a simple circuit example of AGC, not tested in a workbench. This paper ends with an analogic retrofit of a governor of Francis turbine of decade of 1960 of 180 MW using analogic electronic. The author employs IC 741 operational amplifier. Prior simulations of the Laplace’s model of the governor were made using Matlab-Simulink. Because of the little acquisition time of the available oscilloscope, the author made a transformation in the original Laplace model that reduced the step response time by a factor of 20 but the methodology and know-how to make an analogic retrofit was conquered. The governor was built and tested in a workbench. The hydraulic circuit was simulated with 741 amp ops. The electronic simulation corresponded to the mathematics simulations showing the success of the analogic retrofit. The physical space needed by the equipment was reduced from the size of a refrigerator to a size of a shoe box. Although an analogic retrofit is considered obsolete today, the analogic retrofit has robustness, and it is cheaper.

Experimental investigation of an adjustable guide vane system in a Francis turbine draft tube at part load operation

Hydraulic turbines are increasingly used to regulate the electrical grid. They thus have to operate more often at off-design conditions where instabilities may develop leading to large pressure pulsations decreasing the life of the machines. In the present study, an adjustable guide vane system in the draft tube of a single regulated hydraulic turbine is developed. The aim is to mitigate the pressure pulsations when the turbine operates at part load operational regimes without significantly compromising the hydraulic efficiency of the turbine. The draft tube guide vane system, named DTGV, is composed of three guide vanes. Each guide vanes comprise two individual hydrofoils. The upper hydrofoil can rotate around an axis up to ±45°, and the lower is fixed. Therefore, the guide vanes are adjustable. The rotating vortex rope mitigation was investigated at two part-load operational regimes at a 12 m turbine head, a) Q/QBEP = 0.59, and b) Q/QBEP = 0.71. The results indicate that the DTGV system significantly mitigates the pressure pulsations, thereby improving the flexible operation of the turbine. The best mitigation outcome was for 0 GV configuration at both part-load operating conditions. The mitigation effects are better when the operating condition approaches BEP, and the rotating mode of the pressure pulsations tends to go towards the runner frequency (f/f0 = 1). The hydraulic efficiency is found to be marginally affected by the guide vane system at part load operations and is improved at the best efficiency point (Q/QBEP = 1) and high load Q/QBEP = 1.21.

Cavitation Hydrodynamic Performance of 3-D Printed Highly Skewed Stainless Steel Tidal Turbine Rotors

Hydraulic turbines contribute to 60% of renewable energy in the world; however, they also entail some adverse effects on the aquatic ecology system. One such effect is their excessive noise and vibration. To minimize this effect, one of the most effective and feasible solutions is to modify the design of the turbine rotor blade by introducing a skew. In this study, two 0.3-meter tidal turbines with 0-degree (no-skewness) and positive 90-degree skewness made of stainless steel 316L were designed and printed using a 3-D printing powder bed fusion technique. These rotors were then tested at the Emerson Cavitation Tunnel (ECT) at Newcastle University, UK, and the variation in the skewness of the blades of the turbines as a function of the power coefficient on a given tip speed ratio (TSR) value was ascertained. Results showed that the highly skewed rotor had significantly lower drag and torque fluctuations, with a slight decrease in efficiency compared to the non-skewed one, which warrants further investigation on the effect of added skew to reduce vibration and noise. Numerical simulations were also performed for verification and validation of the experimental tests, using the H45 dynamometer at the ECT. A comprehensive software code for propellers and tidal turbines, ROTORYSICS, was used to examine the cavitation effect of the two rotors; a comparison was made for both, with and without cavitation. The results indicate that for a high immersion depth of tidal turbine rotors, cavitation rarely occurs, but for hydrokinetic turbines that are installed on dams in rivers and falls, cavitation could be a serious concern. It was concluded that the 0-degree skewed rotor is more hydrodynamically efficient than the 90-degree skewed rotor.

Experimental and numerical investigation on the dynamic behavior of two partially overlapped identical plates submerged in water

Partially overlapped plates submerged in water are of interest in some industrial applications such as in blade-adjustable hydraulic turbine runners, where the neighboring blades become closer and partially overlapped for certain operating conditions. To know the influence of partially overlapped structures on their dynamic behavior is of great importance to avoid resonances and therefore to extend their lifetime. In this paper, the dynamic behavior of two identical rectangular plates with a partially overlapped area in water has been studied experimentally and numerically. An experimental test rig has been constructed, which consists of two identical rectangular plates in a tank full of water. The distance and the overlapped area between the two plates can be changed to investigate their influence on the added mass, added damping and mode shapes. A finite element method model based on acoustic fluid-structure interaction was used to simulate the added mass effect of the plates from the surrounding water. A theoretical equation used to calculate the damping ratios of submerged structures has also been proposed. Theoretical, experimental and numerical results have been compared and analyzed.

Influence of Installation Deviation of Thrust Bearing on Oil Film Flow of 1000 MW Hydraulic Turbine Unit

The thrust bearing, as the only part bearing the axial load, is extremely important in vertical hydroelectric generating units. Its working condition directly affects the safe and reliable operation of the hydroelectric generating unit. However, during operation, the oil film is easily damaged under the influence of complex factors. Installation deviation is a key point that can cause temperature and pressure changes in the oil film, affecting the force on the bearing. This article takes the thrust bearing model of the 1000 MW Francis turbine unit of the Baihetan Power Station as the research object. Based on the fluid–solid coupling theory and CFD technology, the oil film characteristics of thrust bearings are analyzed, and the influence of inclination angles and installation deviation on the oil film flow performance of thrust bearings is discussed. The results show that as the inclination angle changes from 0.0030° to 0.0048°, the axial force changes from 856 t to 368 t, and there is an approximate linear correlation between them. The radial installation deviation has an effect on the axial force. Under the optimal working condition of an inclination angle of 0.0039°, when the radial deviation of the pad changes from 0 mm to 1 mm, the axial force changes from 1573 t to 1275 t. In the process of unit installation, it is necessary to pay attention to the installation deviation of the pad. The results provide guidance for the installation of the bearing, which helps to ensure the safe and stable operation of the station.

Common Failures in Hydraulic Kaplan Turbine Blades and Practical Solutions.

Kaplan turbines, as one of the well-known hydraulic turbines, are generally utilized worldwide for low-head and high-flow conditions. Any failure in each of the turbine components can result in long-term downtime and high repair costs. In a particular case, if other parts are damaged due to the impact of the broken blades (e.g., the main shaft of the turbine), the whole power plant may be shut down. On the other hand, further research on the primary causes of failures in turbines can help improve the present failure evaluation methodologies in power plants. Hence, the main objective of this paper is to present the major causes of Kaplan turbine failures to prevent excessive damage to the equipment and provide practical solutions for them. In general, turbines are mainly subjected to both Internal Object Damage (IOD) and Foreign Object Damage (FOD). Accordingly, this paper presents a state-of-the-art review of Kaplan turbine failures related to material and physical defects, deficiencies in design, deficits in manufacturing and assembly processes, corrosion failures, fatigue failure, cavitation wear, types of cavitation in hydro turbines, hydro-abrasive problems, and hydro-erosion problems. Eventually, the authors have attempted to discuss practical hints (e.g., nanostructured coatings) to prevent damages and improve the performance of Kaplan turbines.

Reconstruction of integrated hydraulic turbine characteristics curve based on classification weight neural network

To address the shortcomings in the drawing and processing of comprehensive characteristic curves of hydraulic turbines and the problems in the operation and management of small hydropower stations, this paper proposes a method for reconstructing the comprehensive characteristic curves based on classification weight neural network. Firstly, this study discretizes the comprehensive characteristic curve of the target turbine factory package to obtain multiple sets of discrete data points, and compares them with the actual operating data of small hydropower plants, and then pre-processes the operating data by the type and operating characteristics of the unit. Next, this paper uses XGBoost to classify the two types of data to obtain the leaf node optimal scores and uses the scores as the prediction weights of the deep neural network to grid the discrete points of the hydraulic turbine for prediction, and finally obtains the specific integrated characteristic graph of the unit. The method based on classification weight neural network can substantially improve the accuracy and reliability of composite characteristic curves while avoiding multivariate nonlinear mathematical problems, which provides a new method and idea for the reconstruction and expansion of the hydraulic turbine characteristic curve, and also provides a theoretical basis for the safe and economic operation of hydropower units.

The effect of Ni201 transition layer on the corrosion, wear and synergetic cavitation erosion-corrosion behavior of CMT-Monel K500 coating

The Monel K500 modified coating with Ni201 as the transition layer was prepared on the 304 stainless steel substrate by cold metal transfer (CMT) technology. Different from the Monel K500 coatings with direct deposition, the Ni201 transition layer can effectively block the diffusion of Fe and other elements in the substrate and avoid the deterioration of corrosion resistance of Monel K500 coating caused by galvanic corrosion in artificial seawater, which showed the highest polarization resistance and the strongest passivation tendency. In addition, the diffusion of Ni atoms in the transition layer compensated and stabilized the alloy element composition of the Monel K500 coating, making it have a finer microstructure and show higher microhardness and wear resistance. After 10 h- cavitation erosion (CE), the Monel K500 coating with transition layer showed the lowest mean depth erosion rates (MDER) of 2.2 ± 0.09 μm/h as it maintains the highest self-healing ability and integrity of passive film during the long-term synergistic effect of cavitation erosion and corrosion (SCEC). The introduce of the Ni201 transition layer can effectively improve the corrosion-cavitation and wear properties of CMT-Monel K500 surface modified coating, and then effectively prolong the service life of seawater overflow components such as butterfly valves, pump bodies, hydraulic turbines and heat exchangers, which has great application potential in the field of tribo-corrosion in ocean engineering.

Nonlinear controller design for hydraulic turbine regulating systems via immersion and invariance

This paper proposes a nonlinear controller strategy for the frequency regulation of a hydraulic turbine regulating system (HTRS). An immersion and invariance (I&I) technique is utilised to develop the desired control law. The derived control method is used to guarantee that the equilibrium point is asymptotically stable. Furthermore, it can ensure that all overall closed-loop system trajectories are bounded. The feasibility and effectiveness of the technique are demonstrated using a nonlinear dynamical system of an HTRS connected to a single-machine infinite bus (SMIB) power system. The simulation results demonstrate that the technique is capable of regulating the frequency and improving dynamic performance despite large disturbances. It is capable of rapidly reducing oscillations and surpasses two known nonlinear controllers, namely the synergetic control and the backstepping control techniques. Additionally, despite the fact that the HTRS's parameters vary, the proposed technique is capable of providing consistent control performance. As a result, the presented controller is insensitive to variations in the system's parameters.

Hamiltonian Additional Damping Control for Suppressing Power Oscillation Induced by Draft Tube Pressure Fluctuation

The power oscillation induced by pressure fluctuation in the draft tube of the hydraulic turbine is one of the limiting factors preventing the Francis turbine from operating in the vibration zone. At the present power grid with a high proportion of renewable energy resources, we try to improve the load regulation ability of the hydropower units by extending the stable operation zone to the vibration zone. By the mathematical modelling of pressure fluctuation, this paper gives an analytical expression of the power oscillation. We derive the extended Hamiltonian model of the hydropower unit where power oscillation is external excitation. Secondly, the damping injection method introduces some desired interconnection and damping matrices as the Hamiltonian damping factor into the additional damping control. Finally, through theoretical analysis and experimental simulation, this research discusses the resonance characteristics of pressure fluctuation and power oscillation, the equivalent analysis between the damping factor and equivalent damping coefficient, and the control design of vibration zone crossing during the start-up. Simulation results show that when r25 = 1.3, the minimum power oscillation amplitude is 0.5466, which is equivalent to an increase in D by 20. The maximum oscillation amplitude decreases by 4.6%, and the operation limited zone is reduced by 10.1%. The proposed additional damping control can effectively suppress the power oscillation and expand the regulation range.

Multi-objective optimization of an axial flow hydraulic turbine with a collection device to be installed in an open channel

In this study, a multi-objective optimization design method was developed by combining, among other methods, single-phase flow analysis and the optimization method to simultaneously optimize the runner and collection device of an axial-flow hydraulic turbine with a collection device, using the power coefficient and axial thrust coefficient as objective functions. To verify the effectiveness of this design method, the characteristics of the optimized turbine were investigated through verification experiments and multiphase flow analysis, and were compared with the results of single-phase flow analysis. The results of single-phase flow analysis showed that the axial thrust coefficient of the optimized turbine was equivalent to that of the original turbine, while the power coefficient improved dramatically. However, the results of the multiphase flow analysis showed that although the axial thrust coefficient of the optimized turbine was increased compared to that of the original turbine, the power coefficient was significantly higher than that of the results in the single-phase flow analysis, due to a significant increase in the efficiency of the turbine, as well as an increase in the loading coefficient and the inlet velocity ratio, unlike the single-phase flow analysis. This indicates that this design method is effective in terms of output improvement.

Hydrogenerator early fault detection: Sparse Dictionary Learning jointly with the Variational Autoencoder

Monitoring the continuous health status of a Hydraulic Turbine Generator Unit (HTGU) is a strategic task to prevent any unexpected downtime. In addition to the loss of energy production following a prolonged shutdown, the various maintenance costs represent an undesirable effect due to unanticipated failure. One of the main functions of a condition-based maintenance (CBM), is the early detection of any unexpected changes in a machine behavior. Indeed, being able to detect any drift or change in behavior compared to a reference behavior represents a major challenge in the monitoring of complex machines like a HTGU. In this paper, an early anomaly detection model for HTGU using Variational Autoencoders (VAEs) and Sparse Dictionary Learning (SDL) is proposed. The combined reconstruction error thus obtained from the VAE-SDL model is used as an early fault detection. Experimental tests on vibratory signals show that the two models thus joined increase the sensitivity as well as the robustness of the anomaly detection.

Ultrasonic in-situ measurement method and error analysis of wear of PEEK water-lubricated bearing materials

Water-lubricated polymer bearing is the key component to guarantee the function of ship propulsion systems, nuclear main pumps, hydraulic turbines and other important equipment. Abnormal wear of the water-lubricated polymer thrust bearing is a common failure under harsh working conditions such as low speed, heavy load, and sediment. Accurate acquisition of bearing wear is of great value for revealing the bearing wear mechanism and evaluating the bearing service life. Therefore, this paper proposes an in-situ measurement method of bearing wear based on ultrasound and parameter inversion. The objective function is defined as the correlation coefficient of the ultrasonic reflection coefficient amplitude spectrum. Different parameters, such as thickness, acoustic velocity, density and attenuation factor, are inverted by the particle swarm algorithm. Simulations are performed to analyze the influence of single-parameter to multi-parameter inversions on the objective function and the inversion of thickness. Taking the PEEK material as the subject, the experiment shows that the parameter inversion of thickness, density and attenuation factor has the highest accuracy, with errors within 0.15%, 2% and 95%, and the maximum absolute error of wear is 20 μm. If the amplitude of the reflected signal is small, the intensity of the transmission signal will affect the identification result of thickness.

Establishment of correlation for the pressure fluctuations on the low-head Francis turbine in the draft tube cone from the model test

Pressure fluctuation is an essential metric for assessing the effectiveness of the functioning of a hydraulic turbine. During the operation of the hydraulic turbine, pressure fluctuations occur under varied load conditions. An advanced data acquisition system and measurement setup were designed to investigate the pressure fluctuation characteristics in the Francis turbine model with three pressure heads. The operating points for pressure fluctuations investigations ranged from lower part load to overload condition. The plant sigma condition is studied extensively under three different heads, i.e. 30.45 m, 31.98 m and 38.78 m. The miniature-type pressure transducers are used for the investigations. Three pressure sensors, one in the inlet of the spiral case, second and third in the draft tube upstream and downstream respectively, are installed. The measurements were conducted in different operating conditions considering the prototype output power of 16.7 MW, 20.3 MW, 27.8 MW, 34.3 MW and 40.4 MW. A correlation has been developed to represent the variation of draft tube cone pressure fluctuations concerning head and output power.