Hydraulic Runner Research Articles

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.

Experimental Investigation of a Free Runner Concept Downstream of Francis Turbines

The main purpose of the paper is to investigate experimentally a new concept by using a free runner downstream of the main hydraulic runner turbine to increase the flexibility in operation. The free runner concept supposes that rotates at the runaway speed with vanishing mechanical torque. The main purpose is to redistribute between the shaft and the periphery the total pressure and the moment of momentum, such that the flux of total pressure and the moment of momentum are not altered. Moreover, the free runner does not modify the operating point of the main hydraulic turbine runner. The experimental investigation focuses on velocity profiles measurements with the LDV system and the unsteady pressure measurements downstream the free runner, in the draft tube cone.

Comparison of FeMnCrSi Cavitation Resistance Coatings Deposited by Twin-Wire Electric Arc and High-Velocity Oxy-Fuel Processes

The hydraulic runners and many other components are exposed to cavitation phenomena and the erosion occurs, and normally are repaired by arc welding processes. However, the heat input from the welding causes microstructural changes in the components materials. Considering the martensitic stainless steel CA6NM, the welding thermal cycle reduces its fracture toughness and consequently the structural integrity of the equipment. Thermally sprayed coatings are an alternative to repair low eroded areas of these components, since the thermal sraying processes do not change the substrate microstructure and/or mechanical properties as the welding process. Different FeMnCrSi alloys deposited by Twin-Wire Electric Arc (TWEA) or High-Velocity Oxy-Fuel (HVOF) are on development and their cavitation resistance, comparable to the substrate CA6NM, are the object of the study in this research. This work presents the comparison of the deposition characteristics and properties of different FeMnCrSi alloys chemical compositions coatings obtained by TWEA and HVOF processes, evaluating the particles in-flight, morphology, hardness, adherence, and cavitation resistance of the coatings.

Welding and Thermal Spray Processes for Maintenance of Hydraulic Turbine Runners: Case Studies

Abstract: Hydraulic runners are susceptible to failures by cracks or wear by erosion, corrosion, or cavitation. The modern runners are fabricated in carbon steel and martensitic stainless steel. Arc welding processes normally do the repair of eroded areas, or cracked parts. Each material or type of repair needs specific criteria, procedures, and precautions to guarantee their success and prevent future issues, like the recurrence of the cracks or reduction of the useful life of the runner by modifications of the original material. Wear-resistant coatings are applied by welding or by thermal spray processes, considering this last one has no metallurgical interaction with the material of the runner, keeping the original properties of the material. For several years the companies Copel GeT, Lactec, UTFPR, and UFPR collaborate on the study of different techniques, methods, and processes to repair hydraulic runners, this work aims to present a short compilation, and examples of some results obtained applied on real runners.

Fatigue assessment of high strength welded joints through the strain energy density method

AbstractThe main aim of the present work is to investigate, through the strain energy density method, the fatigue behaviour of high strength welded joints realised employed in hydraulic runner blades. The geometries, found in literature, present the welding bead machined in order to have no geometrical discontinuities in the specimen realising a wide fitting radius between the two welded plates; the only critical geometrical discontinuity in the specimen is given by the lack of penetration that leads to an internal crack‐like defect. The specimens presented failure both from the weld toe and from the weld root depending on the amount of welding penetration. The results, summarised in this work with the strain energy density method, show clearly the possibility to consider a unique master curve for this kind of joints regardless of the failure initiation point. Acquiring, through a finite element model, the strain energy density value both at the weld toe and at the weld root and comparing them, the method is proved to be adequate to detect the most critical area of the joint. A first fatigue master curve in terms of cyclic averaged strain energy density value is provided for the fatigue design of high strength welded joints.

Engineering & Performance of DuoTurbo: Microturbine with Counter-Rotating Runners

Considering the nuclear phase-out strategy of several European countries and the future tendency to promote renewable energies, the exploitation of small hydropower sites (<10 MW) becomes increasingly important. In this framework DuoTurbo Turbine, a new DuoTurbo-microturbine prototype for drinking water networks has been jointly developed by the HES-SO Valais//Wallis, the EPFL-Laboratory for Hydraulic Machines and industrial partners. The modular in-line “plug & play” technology requires low investment, reaching economic feasibility with an available power between 5 kW and 25 kW. One stage of the microturbine consists of two axial counter-rotating runners that form a compact independent unit. Each runner of the turbine holds its own rim generator, the DuoTurbo-configuration involving that each hydraulic runner is integral with each electrical rotor. The possibility of stacking several stages in series enables covering quite a wide range of hydraulic power and, thus, recovering a maximum of energy dissipated in release valves of water supply systems. The present work introduces the global concept of the implemented prototype of the DuoTurbo-microturbine, to target a maximal injected power of 5 kW for a discharge of 9 l/s and a head of 24.5 m per stage. The main features of the hydraulic, the mechanical, the electrical and the electronic design are presented. The hydraulic performance is, then, assessed using CFD simulations for the expected operating range. Finally, the performance measurements of the single-stage prototype installed in the hydraulic test rig of the HES-SO Valais//Wallis are presented.

Feasibility of using PZT actuators to study the dynamic behavior of a rotating disk due to rotor-stator interaction.

In this paper, PZT actuators are used to study the dynamic behavior of a rotating disk structure due to rotor-stator interaction excitation. The disk is studied with two different surrounding fluids—air and water. The study has been performed analytically and validated experimentally. For the theoretical analysis, the natural frequencies and the associated mode shapes of the rotating disk in air and water are obtained with the Kirchhoff-Love thin plate theory coupled with the interaction with the surrounding fluid. A model for the Rotor Stator Interaction that occurs in many rotating disk-like parts of turbomachinery such as compressors, hydraulic runners or alternators is presented. The dynamic behavior of the rotating disk due to this excitation is deduced. For the experimental analysis a test rig has been developed. It consists of a stainless steel disk (r = 198 mm and h = 8 mm) connected to a variable speed motor. Excitation and response are measured from the rotating system. For the rotating excitation four piezoelectric patches have been used. Calibrating the piezoelectric patches in amplitude and phase, different rotating excitation patterns are applied on the rotating disk in air and in water. Results show the feasibility of using PZT to control the response of the disk due to a rotor-stator interaction.

Multi-fidelity design optimization of Francis turbine runner blades

A robust multi-fidelity design algorithm has been developed, focusing to efficiently handle industrial hydraulic runner design considerations. The computational task is split between low- and high-fidelity phases in order to properly balance the CFD cost and required accuracy in different design stages. In the low-fidelity phase, a derivative-free optimization method employs an inviscid flow solver to obtain the major desired characteristics of a good design in a relatively fast iterative process. A limited number of candidates are selected among feasible optimization solutions by a newly developed filtering process. The main function of the filtering process is to select some promising candidates to be sent into the high-fidelity phase, which have significantly different geometries, and also are dominant in their own territories. The high-fidelity phase aims to accurately evaluate those promising candidates in order to select the one which is closest to design targets. A low-head runner case study has shown the ability of this methodology to identify an optimized blade through a relatively low computational effort, which is significantly different from the base geometry.

Hydraulic Runner Design Method for Lifetime

Quest for reliability of hydraulic runners is a concern for all mature electricity producers. The fatigue damage caused by dynamics loads is frequently the root cause of runner failure. This paper presents the damage tolerance approach based on fracture mechanics as the method chosen by Alstom and Hydro-Qu<TEX>$\acute{e}$</TEX>bec to predict effects of damage on runner lifetime and consequently to be use as a design method. This is sustained by a research on fracture mechanics properties of runner materials and by recommendations on the strategy to define a safety margin for design. The acquired knowledge permits to identify potential improvement of the runner lifetime without significant cost increase, like being more specific on some chemical composition or heat treatment.

New parameters influencing hydraulic runner lifetime

Traditionally, hydraulic runner mechanical design is based on calculation of static stresses. Today, validation of hydraulic runner design in terms of reliability requires taking into account the fatigue effect of dynamics loads. A damage tolerant approach based on fracture mechanics is the method chosen by Alstom and Hydro-Québec to study fatigue damage in runners. This requires a careful examination of all factors influencing material fatigue behavior. Such material behavior depends mainly on the chemical composition, microstructure and thermal history of the component, and on the resulting residual stresses. Measurement of fracture mechanics properties of various steels have demonstrated that runner lifetime can be significantly altered by differences in the manufacturing process, although remaining in accordance with agreed practices and standards such as ASTM. Carbon content and heat treatment are suspected to influence fatigue lifetime. This will have to be investigated by continuing the current research.

Modelling and simulation of the electric slag remelting guide vane casting (ESRC) process and its application

Modelling and experiment work is carried out for a large stainless steel casting with variable cross-section and a curved surface which is produced by the electric slag remelting casting process. The casting is part of a hydraulic runner generator at a power station of a big river.Mathematical models of the heat transfer and melted rate from an expendable metallic electrode were established. The melted rate is related to some important parameters, such as electric current and voltage, temperature and the flow rate of the cooling water in a crystallizer. Electrode melting, the moving pattern of the melted pool and the slag pool and the melt solidification in the metal pool were simulated.In order to make the enmeshment of the variable curved surface of the casting, a co-operation method of extended constructive solid geometry (CSG) from 9 to 21 uniform geometry with B-Spline surface functions is developed. By this method the guide vane casting is enmeshed. The boundary condition between the steel casting and the crystallizer cooled by water was measured.Based on the above new content the solidification simulation software ESRC3D is developed. Using it to simulate the whole process of ESRC with different parameters, instead of exploring the technological parameters of casting production by the trail-and-error method, the optimized parameters from the simulation for production of the large stainless steel castings with variable cross-section and a curved surface, such as the guide vane castings, have been used to produce them. Economic benefit and good quality of castings are obtained. Guide vane castings are widely applied to the hydraulic runner generator at numerous river power stations.

Turbulent Flow Simulation of a Runner for Francis Hydraulic Turbines Using Pseudo-Compressibility

A three-dimensional Navier-Stokes code with pseudo-compressibility, an implicit formulation of finite difference, and a k – ε two-equation turbulence model has been developed for the Francis hydraulic runner. The viscous flow in the rotating field can be simulated well in the design flow operating condition as well as in the off-design conditions in which a strong vortex occurs due to the separation near the leading edge. Because the code employs an implicit algorithm and a wall function near the wall, it does not require a large CPU time. It can therefore be used on a small computer such as the desk-top workstation, and is available for use as a design tool. The same kind of algorithm that is used for compressible flows has been found to be appropriate for the simulation of complex incompressible flows in the field of turbomachinery.

Static and dynamic calculation of a Francis turbine runner with some remarks on accuracy

The work presented in this paper describes both the static deformation under centrifugal forces and water pressure, and the natural vibrations of a hydraulic runner of the Francis type. First, the method of calculation is described; it uses finite elements and considers only one sector of the structure with appropriate boundary conditions. Second, preliminary test calculations with two simple bodies are shown; these tests were performed in order that we might familiarise ourselves with the method, in particular with the plane and curved shell elements used, and they had to provide information about the accuracy that could be expected from the results. Finally, several calculations of the Francis runner are presented and their main features are discussed.

水車ランナー用17Cr-5Ni-1Mo鋳鋼の耐食性と機械的性質

水車ランナー用17Cr-5Ni-1Mo鋳鋼の耐食性と機械的性質

A NEW “SHEET FLOW” HYDRAULIC RUNNER

The efficiency of hydraulic rotors depends upon accurate design and precise production of geometric surfaces. Compromise contours to promote strength are required for high speed rotors. In this article Mr. Schmidt describes a method of accomplishing these criteria. In addition he offers a welcome simplicity of procedure.