Wicket Gate Research Articles

Investigation of distributor vane jets to decrease the unsteady load on hydro turbine runner blades

As the runner blades of a Francis hydroturbine pass though the wakes created from the wicket gates, they experience a significant change in absolute velocity, flow angle, and pressure. The concept of adding jets to the trailing edge of the wicket gates is proposed as a method for reducing the dynamic load on the hydroturbine runner blades. Computational experiments show a decrease in velocity variation experienced by the runner blade with the addition of the jets. The decrease in velocity variation resulted in a 43% decrease in global torque variation at the runner passing frequency. However, an increased variation was observed at the wicket gate passing frequency. Also, a 5.7% increase in average global torque was observed with the addition of blowing from the trailing-edge of the wicket gates.

Numerical study of pressure fluctuations in different guide vanes' opening angle in pump mode of a pump turbine

A numerical model based on a pumped storage power station was built to develop the numerical simulation, to analyze the pressure fluctuations in a pump turbine in different guide vanes' opening angle. The different guide vanes' opening angles were simulated using the SST k-ω turbulence model and SIMPLEC Pressure-Velocity coupling scheme. The pressure sensor were placed in mainly three positions, they are: bottom ring between runner and the wicket gates, downstream and left side in the draft tube cone below the runner. All the peak to peak values of pressure fluctuation meet signal probability of 97%. The frequency is gained by Fast Fourier Transform. The pressure fluctuations in different positions of the model in pump condition were showed when the guide vanes' opening angels were different. The simulation results confirmed the results gained in model tests. The results show that pressure fluctuations in design opening angle were much lower than those in off design opening angle. The main source of pressure fluctuations between runner and guide vanes is rotor stator interaction. While a lower frequency is the main frequency of the pressure fluctuation in draft tube.

Force Analysis of Ring Gate Based on ANSYS

Ring gate of Ahai hydropower Station is known to the highest ring gate in the world. In this paper, it is calculated to the driving loads of the Ahai ring gate by six hydraulic servomotors during a closure without automatic control (i.e. in case of a breakdown of the electrical control system), analyzed the behavior of the operating system of the ring gate closure with the water discharge and closure with three wicket gates not synchronized (i.e. three wicket gates remained accidentally in open position), and finally shown to how the 6 servomotors are synchronized on the basis of the driving loads. There are proved to The feasibility and the credibility of this system of ring gate by using ANSYS to a case.

Experimental study of the pressure fluctuations in a pump turbine at large partial flow conditions

Frequent shifts of output and operating mode require a pump turbine with excellent stability. Current researches show that large partial flow conditions in pump mode experience positive-slope phenomena with a large head drop. The pressure fluctuation at the positive slope is crucial to the pump turbine unit safety. The operating instabilities at large partial flow conditions for a pump turbine are analyzed. The hydraulic performance of a model pump turbine is tested with the pressure fluctuations measured at unstable operating points near a positive slope in the performance curve. The hydraulic performance tests show that there are two separated positive-slope regions for the pump turbine, with the flow discharge for the first positive slope from 0.85 to 0.91 times that at the maximum efficiency point. The amplitudes of the pressure fluctuations at these unstable large partial flow conditions near the first positive slope are much larger than those at stable operating condtions. A dominant frequency is measured at 0.2 times the impeller rotational frequency in the flow passage near the impeller exit, which is believed to be induced by the rotating stall in the flow passage of the wicket gates. The test results also show hysteresis with pressure fluctuations when the pump turbine is operated near the first positive slope. The hysteresis creates different pressure fluctuations for those operation points even though their flow rates and heads are similar respectively. The pressure fluctuation characteristics at large partial flow conditions obtained by the present study will be helpful for the safe operation of pumped storage units.

Polar gridline transformation method on nearly uniform cell areas and line spacing inside circular geometries

A novel derivation to transfer an actual domain with circular geometries to the computational domain, which is competent for application to computational fluid dynamics, is derived. Outcome formulas could be employed in cases of gridline transformation in the method of linearized, two dimensional fluid transients, as well. In addition, hydraulic parameters can be computed and handled to achieve high precision results, which is called the polar gridline transformation method. This method is used in cases of other kinds of non-prismatic sections or complex shaped domains, such as the turbine spiral case or the specific shape around wicket gates, and the turbine runner. A real example is also illustrated to verify the necessity and validity of the derived formulas, and logical conclusions are included.

NUMERICAL SIMULATION OF HIGH REYNOLDS NUMBER TURBULENT FLOW IN A VANE PASSAGE

The numerical simulations of two-dimensional high Reynolds number turbulent flow in a guide vane passage of a Francis hydro turbine are performed successfully by using the unstructured dynamic mesh model for moving body. The standard K – ε turbulence model is employed for the simulation of turbulence. The pressure-velocity coupling method is realized with the SIMPLEC algorithm. The temporal distributions of the pressure and turbulent viscosity in a passage were obtained in the closing of wicket gate on a platform of the software ANSYS FLUENT. The results show that the evolution of the flow field is unsteady with decrease of the geometrical opening of the gate. The details of the flow changes are obtained in the moving rigid body domain. The method can be used to simulate the high Reynolds number incompressible turbulent flow with moving boundary. The calculation provides some references for vortex-induced vibration of the structure in a complex turbulent flow.

The possibility to increase the rated output as a result of index tests performed in Iron Gates II- Romania

The Index Tests have been used for many years to obtain the optimized cam corellation between wicket gates and runner blades for double regulated turbines (Kaplan, bulb). The cam is based on homologous model tests and is verified by site measurements, as model tests generally do not reproduce the exact intake configuration. Index Tests have also a considerable importance for checking of the relative efficiency curve of all type of turbines and can demonstrate if the prototype efficiency curve at plant condition has the shape expected from the test of the homologues model. During the Index Tests measurements the influence of all losses at multiple points of turbine operation can be proved. This publication deals with an overview on the Index Tests made after modernization of large bulb units in Iron Gates II – Romania. These field tests, together with the comparative, fully homologous tests for the new hydraulic shape of the runner blades have confirmed the smooth operational behavior and the guaranteed performance. Over the whole "guaranteed operating range" for H = 8m, the characteristic of the Kaplan curve (enveloping curve to the proppeler curves), agreed very well to the predicted efficiency curve from the hydraulic prototype hill chart. The new cam correlation have been determined for different head and realised in the governor, normally based on model tests. The guaranteed, maximum turbine output for H = 7,8m is specified with 32, 5 MW. The maximum measured turbine output during the Index Tests on cam operation was 35,704 MW at the net head of 7,836 m. This coresponds to 35,458 MW for the specified head H= 7, 8 m. All these important improvements ensure a significant increase of annual energy production without any change of the civil construction and without increasing the runner diameter. Also the possibility to increase the turbine rated output is evident.

High-speed flow visualization in a pump-turbine under off-design operating conditions

The flow hydrodynamics in a low specific speed radial pump-turbine reduced scale model is experimentally investigated under off-design operating conditions in generating mode. Wall pressure measurements, in the stator, synchronized with high-speed flow visualizations in the vaneless space between the impeller and the guide vanes using air bubbles injection are performed. When starting from the best efficiency point and increasing the runner speed, a significant increase of the pressure fluctuations is observed mainly in channels between wicket gates. The spectral analysis shows a rise of one stall cell, rotating with about 70% of the impeller frequency, at runaway, which further increases as the zero discharge condition is approached. Then a specific image processing technique is detailed and applied to create a synthetic instantaneous view of the flow pattern on the entire guide vanes circumference for an operating point in turbine-brake mode, where backflow and vortices accompany the stall passage.

Simulation of Transient Flow in Hydroelectric Power Plants Using Unsteady Friction

In this paper the influence of surge tanks on transient flow generated by changing turbine gate opening has been numerically studied. For this purpose, the governing equations of transient flow are solved using the method of characteristics and considering unsteady friction. The surge tank and the hydraulic turbine are considered as internal boundary conditions. Comparison of transient results for pressure oscillations with the available experimental data shows good agreement. The surge tanks lower down the pressure levels at the upstream side of turbine and stabilize the pressure at the downstream side. Also, surge tanks delay the time occurrence of the maximum and minimum pressure. Finally, the effect of wicket gate closing followed by wicket gate opening on the so called speed no load operation (SNLO) on the transient flow is investigated and transient conditions improved by this sequence are found.

Bending fatigue of stainless steel shear pins belonging to a hydroelectric plant

Coaracy Nunes was the first hydroelectric power plant in the Amazon region, being located in Araguari River, Amapá State, Brazil. The plant operates since 1976, presenting now a nominal capacity of 78 MW. The shear pins, which are installed in the turbine hydraulic arms to control the wicket gate and regulate the water flow into the turbine blades, suffered several breakdowns since 2004. These shear pins are made of an ASTM 410 stainless steel and were designed to break by a shear overload of 120 kN. Fractographic investigation of the pins, however, revealed two types of fracture topographies: a region of stable crack propagation area, with non-pronounced striation and secondary cracks; and a region of unstable propagation, featuring elongated dimples. These results indicated that the stable crack propagation occurred by fatigue (bidirectional bending), which was nucleated at machining marks under high nominal load. Finite element analysis was carried out using two loading conditions (pure shear and a combination of shear and bending) and the results indicated that the presence of a bending stress strongly increased the stress concentration factor (85% rise in the shear stress and 130% rise in the Von Mises stress). Misalignment during shear pins assembly associated with vibration might have promoted the premature failure of the shear by bending fatigue.

Efforts to Reduce Mortality to Hydroelectric Turbine-Passed Fish: Locating and Quantifying Damaging Shear Stresses

Severe fluid forces are believed to be a source of injury and mortality to fish that pass through hydroelectric turbines. A process is described by which laboratory bioassays, computational fluid dynamics models, and field studies can be integrated to evaluate the significance of fluid shear stresses that occur in a turbine. Areas containing potentially lethal shear stresses were identified near the stay vanes and wicket gates, runner, and in the draft tube of a large Kaplan turbine. However, under typical operating conditions, computational models estimated that these dangerous areas comprise less than 2% of the flow path through the modeled turbine. The predicted volumes of the damaging shear stress zones did not correlate well with observed fish mortality at a field installation of this turbine, which ranged from less than 1% to nearly 12%. Possible reasons for the poor correlation are discussed. Computational modeling is necessary to develop an understanding of the role of particular fish injury mechanisms, to compare their effects with those of other sources of injury, and to minimize the trial and error previously needed to mitigate those effects. The process we describe is being used to modify the design of hydroelectric turbines to improve fish passage survival.

Development and Evaluation of a New Helical Fish-Friendly Hydroturbine

A new hydroturbine was developed to improve fish survival during their downstream migration. This turbine includes a normal scroll case, few but relatively long wicket gates, a streamlined downturn before the runne rinlet, a runner with only three helical blades attached to a tapered hub and a rotating shroud attached to the outside edges of the blades. After design of the turbine using analytical methods and construction of a 1:3.25 scale pilot turbine and flow loop, engineering studies and tests with live fish were conducted at full-scale heads and velocities. Resulting test data indicated that the full-scale turbine would have an efficiency of about 90% and that fish survival would be about 98% for fish 100 mm (4 in.) long. Survival would be greater for smaller fish and less for larger fish. Various improvements to the turbine design were identified prior to full-scale field application.

Modeling and Control Design for Governing Hydroelectric Turbines With Leaky Wicket Gates

This paper examines a problem of governor control on a set of hydroelectric turbines that suffer from severe wicket gate leakage. Modeling of the system and steady-state behavior of each turbine is used to determine the best means of speed control. The results show that secondary water control devices may be used with the wicket gates to alleviate the effects of leakage in synchronizing the generators to the power system. The control method developed results in two distinct modes of turbine operation, one in the offline mode and the other in the online mode. A digital speed droop governor scheme is considered in the two operating modes by gain scheduling. The results of the implementation of the algorithms in a PLC are presented.

Fitness for purpose assessment after an over pressure incident at Arapuni Power Station

In December 2000 the wicket gates of Arapuni Unit G7 closed rapidly when a control arm separated from a shaft and the wickets were free to move. The unit had been operating under normal conditions at the time. The resulting overpressure pulse caused the lower portion of the penstock to become barrel shaped, and a longitudinal riveted joint partially failed. A significant amount of cracking was visible in the cast steel stay vanes and deformation had occurred at the rivets in the scroll case. A program of work was instigated to determine the cause of the failure, and its consequences, i.e. the pressures reached and what work was required to ensure that the unit was fit for reuse. The root cause of the failure was the design and fabrication of a control arm installed when the wicket gate control system had been modified. This control arm had two segments which clamped around a shaft. The clamping bolts used had seen a high residual bending load and cyclic loading. They failed in fatigue. The coating on the inside of the penstock and scroll casing was brittle and an assessment of the degree of craze cracking in the coating on tensile test specimens allowed an accurate method of determining the plastic strain that had occurred in the penstock, and hence the stress and applied pressure that occurred during the incident. The major issue was the condition of the stay vanes and the rivet holes in the scroll casing. The cracking in them was quantified by NDT inspection. Most of the cracks seen in the stay vanes were original casting defects that had not propagated during the overpressure. An engineering critical assessment was carried out in accordance with recognized international standards to determine the effects of defects under brittle fracture and overload conditions for a range of pressure conditions. An initial assessment was performed using conservative estimated values for the applied stresses and materials properties. The initial calculation indicated that the units were probably fit for purpose. Mechanical testing on samples taken from the stay vane casting and strain gauging during a proof pressure test was carried out. This allowed the calculations to be refined and the confidence in the result to be increased. A fatigue assessment was then carried out in accordance with the standards. The stay vanes and the scroll in the unit were shown to be fit for purpose without any modification and fatigue was not predicted to be a major problem. The unit was returned to service without any modification to the cracked stay vanes. An inspection procedure and regime was also defined to ensure the unit remains fit for purpose.

Comparison of computed water hammer pressures with test results for the Çatalan power plant in Turkey

The closure of a flow control mechanism at the end of a penstock may cause significant transient pressures. The governing equations of this unsteady flow phenomenon, the conservation of mass and conservation of momentum, are solved by the method of characteristics using various computational schemes. A study was carried out to compare the computational results of the transient pressures with measured prototype data for the Çatalan Power Plant in Turkey. Prototype data were collected during the closure of the wicket gates of a Francis turbine from the test procedures of "load rejection", "emergency shut down", and "quick stop". The numerical results for the transient pressures just upstream of the turbine are compared with the measured data. The general agreement between the theoretical and experimental results is found to be quite reasonable.Key words: transient pressure, water hammer, power plant, Francis turbine, penstock, method of characteristics.

Design optimization of axial flow hydraulic turbine runner: Part I—an improved Q3D inverse method

AbstractWith the aim of constructing a comprehensive design optimization procedure of axial flow hydraulic turbine, an improved quasi‐three‐dimensional inverse method has been proposed from the viewpoint of system and a set of rotational flow governing equations as well as a blade geometry design equation has been derived. The computation domain is firstly taken from the inlet of guide vane to the far outlet of runner blade in the inverse method and flows in different regions are solved simultaneously. So the influence of wicket gate parameters on the runner blade design can be considered and the difficulty to define the flow condition at the runner blade inlet is surmounted. As a pre‐computation of initial blade design on S2m surface is newly adopted, the iteration of S1 and S2m surfaces has been reduced greatly and the convergence of inverse computation has been improved. The present model has been applied to the inverse computation of a Kaplan turbine runner. Experimental results and the direct flow analysis have proved the validation of inverse computation. Numerical investigations show that a proper enlargement of guide vane distribution diameter is advantageous to improve the performance of axial hydraulic turbine runner. Copyright © 2002 John Wiley & Sons, Ltd.

HYDRODYNAMIC STUDY OF THE OLMSTED WICKET GATE USING A 1:25-SCALE MODEL

This paper discusses scale-model tests and analytical procedures for investigating structural vibration problems induced by flow-pressure fluctuations. The structure under study is a 1:25-scale model of a curved wicket gate of the Olmsted Locks and Dam. A simplified technique, based on the added-mass concept assuming an incompressible fluid. was developed to incorporate the hydrodynamic effects of the surrounding fluid in the dynamic analysis of this gate. In order to develop a fundamental understanding of the effects of hydrodynamic interaction, the study concentrated on the hypothesis that the fluid–structure interaction involves only the first structural mode of vibration of the gate. Data from the shaft load and upstream pressure, obtained from the experimental tests of the wicket gate, were analysed in order or validate this assumption. The analysis of the data validated the hypothesis. i.e. that the pressure fluctuation and the induced transient dynamic response observed during the experimental tests are related to the first natural frequency of the wicket gate.

Forces on Edge-Hinged Panels in Gradually Varied Flow

This paper describes a mathematical model leading to experimental analysis to estimate the hydraulic forces on a prototype edge-hinged panel (wicket gate) in gradually varied flow. The two-dimensional potential theory of hydrodynamics is used to model the effect of the mean water flow approaching a gate aperture controlled by a hydraulic wicket in a locks-and-dam system. The mean pressure against a typical wicket partially blocking the aperture is then modeled using conformal mapping. The elastic reaction at the supporting shaft of the gate is derived from equilibrium considerations. The effect of the fluctuations of the pressure field about the mean is obtained through an application of the theory of stationary random processes. The total design reaction at the shaft of the wicket is cast in a first-order second-moment format. The theoretical model is compared to experiments on a 1/25-scale physical model. The application of the model in hydraulic design of wicket gates is illustrated by means of a practical example.

Comportement dynamique d'une turbine Kaplan lors d'un arrêt d'urgence - Application au cas de Fessenheim

Following rupture of a blade of the Fessenheim Kaplan turbine, investigations have heen carried out to identify the probable causes, and protective solutions to be implemented. This research has led to modification of the blades and wicket gate movement laws during the release phase, in order to limit the risks linked to: exceeding the maximum speed and pressure allowed, lifting the group, appearance of impacts on the runner and draft tube wall.

Neuro-fuzzy controller of low head hydropower plants using adaptive-network based fuzzy inference system

This paper presents an attempt of nonlinear, multivariable control of low-head hydropower plants, by using adaptive-network based fuzzy inference system (ANFIS). The new design technique enhances fuzzy controllers with self-learning capability for achieving prescribed control objectives in a near optimal manner. The controller has flexibility for accepting more sensory information, with the main goal to improve the generator unit transients, by adjusting the exciter input, the wicket gate and runner blade positions. The developed ANFIS controller whose control signals are adjusted by using incomplete on-line measurements, can offer better damping effects to generator oscillations over a wide range of operating conditions, than conventional controllers. Digital simulations of hydropower plant equipped with low-head Kaplan turbine are performed and the comparisons of conventional excitation-governor control, state-feedback optimal control and ANFIS based output feedback control are presented. To demonstrate the effectiveness of the proposed control scheme and the robustness of the acquired neuro-fuzzy controller, the controller has been implemented on a complex high-order nonlinear hydrogenerator model.