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International journal of fluid machinery and syste...International journal of fluid machinery and systems 22건

  1. [국내논문]   Unsteady Flow with Cavitation in Viscoelastic Pipes  

    Soares, Alexandre K. (Department of Sanitary and Environmental Engineering, Federal University of Mato Grosso ) , Covas, Didia I.C. (Instituto Superior Tecnico, Technical University of Lisbon (TULisbon) ) , Ramos, Helena M. (Instituto Superior Tecnico, Technical University of Lisbon (TULisbon) ) , Reis, Luisa Fernanda R. (Sao Carlos School of Engineering, University of Sao Paulo)
    International journal of fluid machinery and systems v.2 no.4 ,pp. 269 - 277 , 2009 ,

    초록

    The current paper focuses on the analysis of transient cavitating flow in pressurised polyethylene pipes, which are characterized by viscoelastic rheological behaviour. A hydraulic transient solver that describes fluid transients in plastic pipes has been developed. This solver incorporates the description of dynamic effects related to the energy dissipation (unsteady friction), the rheological mechanical behaviour of the viscoelastic pipe and the cavitating pipe flow. The Discrete Vapour Cavity Model (DVCM) and the Discrete Gas Cavity Model (DGCM) have been used to describe transient cavitating flow. Such models assume that discrete air cavities are formed in fixed sections of the pipeline and consider a constant wave speed in pipe reaches between these cavities. The cavity dimension (and pressure) is allowed to grow and collapse according to the mass conservation principle. An extensive experimental programme has been carried out in an experimental set-up composed of high-density polyethylene (HDPE) pipes, assembled at Instituto Superior T $\acute{e}$ cnico of Lisbon, Portugal. The experimental facility is composed of a single pipeline with a total length of 203 m and inner diameter of 44 mm. The creep function of HDPE pipes was determined by using an inverse model based on transient pressure data collected during experimental runs without cavitating flow. Transient tests were carried out by the fast closure of the ball valves located at downstream end of the pipeline for the non-cavitating flow and at upstream for the cavitating flow. Once the rheological behaviour of HDPE pipes were known, computational simulations have been run in order to describe the hydraulic behaviour of the system for the cavitating pipe flow. The calibrated transient solver is capable of accurately describing the attenuation, dispersion and shape of observed transient pressures. The effects related to the viscoelasticity of HDPE pipes and to the occurrence of vapour pressures during the transient event are discussed.

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  2. [국내논문]   Uncertainty in Operational Modal Analysis of Hydraulic Turbine Components  

    Gagnon, Martin (Department of Mechanical Engineering, Ecole de technologie superieure ) , Tahan, S.-Antoine (Department of Mechanical Engineering, Ecole de technologie superieure ) , Coutu, Andre (Andritz-Hydro Ltd)
    International journal of fluid machinery and systems v.2 no.4 ,pp. 278 - 285 , 2009 ,

    초록

    Operational modal analysis (OMA) allows modal parameters, such as natural frequencies and damping, to be estimated solely from data collected during operation. However, a main shortcoming of these methods resides in the evaluation of the accuracy of the results. This paper will explore the uncertainty and possible variations in the estimates of modal parameters for different operating conditions. Two algorithms based on the Least Square Complex Exponential (LSCE) method will be used to estimate the modal parameters. The uncertainties will be calculated using a Monte-Carlo approach with the hypothesis of constant modal parameters at a given operating condition. In collaboration with Andritz-Hydro Ltd, data collected on two different stay vanes from an Andritz-Hydro Ltd Francis turbine will be used. This paper will present an overview of the procedure and the results obtained.

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  3. [국내논문]   Influence of the Francis Turbine location under vortex rope excitation on the Hydraulic System Stability  

    Alligne, S. (Laboratory for Hydraulic Machines, EPFL University ) , Nicolet, C. (Power vision engineering sarl Chemin des champs ) , Allenbach, P. (Laboratory for Electrical Machines, EPFL University ) , Kawkabani, B. (Laboratory for Electrical Machines, EPFL University ) , Simond, J.J. (Laboratory for Electrical Machines, EPFL University ) , Avellan, F. (Laboratory for Hydraulic Machines, EPFL University)
    International journal of fluid machinery and systems v.2 no.4 ,pp. 286 - 294 , 2009 ,

    초록

    Hydroelectric power plants are known for their ability to cover variations of the consumption in electrical power networks. In order to follow this changing demand, hydraulic machines are subject to off-design operation. In that case, the swirling flow leaving the runner of a Francis turbine may act under given conditions as an excitation source for the whole hydraulic system. In high load operating conditions, vortex rope behaves as an internal energy source which leads to the self excitation of the system. The aim of this paper is to identify the influence of the full load excitation source location with respect to the eigenmodes shapes on the system stability. For this, a new eigenanalysis tool, based on eigenvalues and eigenvectors computation of the nonlinear set of differential equations in SIMSEN, has been developed. First the modal analysis method and linearization of the set of the nonlinear differential equations are fully described. Then, nonlinear hydro-acoustic models of hydraulic components based on electrical equivalent schemes are presented and linearized. Finally, a hydro-acoustic SIMSEN model of a simple hydraulic power plant, is used to apply the modal analysis and to show the influence of the turbine location on system stability. Through this case study, it brings out that modeling of the pipe viscoelastic damping is decisive to find out stability limits and unstable eigenfrequencies.

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  4. [국내논문]   Axisymmetric Swirling Flow Simulation of the Draft Tube Vortex in Francis Turbines at Partial Discharge   피인용횟수: 1

    Susan-Resiga, Romeo (Department of Hydraulic Machinery, "Politehnica" University of Timisoara ) , Muntean, Sebastian (Center for Advanced Research in Engineering Science, Romanian Academy - Timisoara Branch ) , Stein, Peter (VA TECH HYDRO ) , Avellan, Francois (Laboratory for Hydraulic Machines, Ecole Polytechnique Federale de Lausanne)
    International journal of fluid machinery and systems v.2 no.4 ,pp. 295 - 302 , 2009 ,

    초록

    The flow in the draft tube cone of Francis turbines operated at partial discharge is a complex hydrodynamic phenomenon where an incoming steady axisymmetric swirling flow evolves into a three-dimensional unsteady flow field with precessing helical vortex (also called vortex rope) and associated pressure fluctuations. The paper addresses the following fundamental question: is it possible to compute the circumferentially averaged flow field induced by the precessing vortex rope by using an axisymmetric turbulent swirling flow model? In other words, instead of averaging the measured or computed 3D velocity and pressure fields we would like to solve directly the circumferentially averaged governing equations. As a result, one could use a 2D axi-symmetric model instead of the full 3D flow simulation, with huge savings in both computing time and resources. In order to answer this question we first compute the axisymmetric turbulent swirling flow using available solvers by introducing a stagnant region model (SRM), essentially enforcing a unidirectional circumferentially averaged meridian flow as suggested by the experimental data. Numerical results obtained with both models are compared against measured axial and circumferential velocity profiles, as well as for the vortex rope location. Although the circumferentially averaged flow field cannot capture the unsteadiness of the 3D flow, it can be reliably used for further stability analysis, as well as for assessing and optimizing various techniques to stabilize the swirling flow. In particular, the methodology presented and validated in this paper is particularly useful in optimizing the blade design in order to reduce the stagnant region extent, thus mitigating the vortex rope and expending the operating range for Francis turbines.

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  5. [국내논문]   Dynamic Analysis of Francis Runners - Experiment and Numerical Simulation   피인용횟수: 1

    Lais, Stefan (ANDRITZ HYDRO Ltd. ) , Liang, Quanwei (ANDRITZ HYDRO Ltd. ) , Henggeler, Urs (ANDRITZ HYDRO Ltd. ) , Weiss, Thomas (ANDRITZ HYDRO Ltd. ) , Escaler, Xavier (Technical University of Catalonia (CDIF-UPC) ) , Egusquiza, Eduard (Technical University of Catalonia (CDIF-UPC))
    International journal of fluid machinery and systems v.2 no.4 ,pp. 303 - 314 , 2009 ,

    초록

    The present paper shows the results of numerical and experimental modal analyses of Francis runners, which were executed in air and in still water. In its first part this paper is focused on the numerical prediction of the model parameters by means of FEM and the validation of the FEM method. Influences of different geometries on modal parameters and frequency reduction ratio (FRR), which is the ratio of the natural frequencies in water and the corresponding natural frequencies in air, are investigated for two different runners, one prototype and one model runner. The results of the analyses indicate very good agreement between experiment and simulation. Particularly the frequency reduction ratios derived from simulation are found to agree very well with the values derived from experiment. In order to identify sensitivity of the structural properties several parameters such as material properties, different model scale and different hub geometries are numerically investigated. In its second part, a harmonic response analysis is shown for a Francis runner by applying the time dependent pressure distribution resulting from an unsteady CFD simulation to the mechanical structure. Thus, the data gained by modern CFD simulation are being fully utilized for the structural design based on life time analysis. With this new approach a more precise prediction of turbine loading and its effect on turbine life cycle is possible allowing better turbine designs to be developed.

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  6. [국내논문]   Overload Surge Investigation Using CFD Data  

    Flemming, Felix (Voith Hydro, Inc. ) , Foust, Jason (Voith Hydro, Inc. ) , Koutnik, Jiri (Voith Hydro Holding GmbH & Co. KG ) , Fisher, Richard K. (Voith Hydro, Inc.)
    International journal of fluid machinery and systems v.2 no.4 ,pp. 315 - 323 , 2009 ,

    초록

    Pressure oscillations triggered by the unstable interaction of dynamic flow features of the hydraulic turbine with the hydraulic plant system - including the electrical design - can at times reach significant levels and could lead to damage of plant components or could reduce component lifetime significantly. Such a problem can arise for overload as well as for part load operation of the turbine. This paper discusses an approach to analyze the overload high pressure oscillation problem using computational fluid dynamic (CFD) modeling of the hydraulic machine combined with a network modeling technique of the hydraulic system. The key factor in this analysis is the determination of the overload vortex rope volume occurring within the turbine under the runner which is acting as an active element in the system. Two different modeling techniques to compute the flow field downstream of the runner will be presented in this paper. As a first approach, single phase flow simulations are used to evaluate the vortex rope volume before moving to more sophisticated modeling which incorporates two phase flow calculations employing cavitation modeling. The influence of these different modeling strategies on the simulated plant behavior will be discussed.

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  7. [국내논문]   Unstable Operation of Francis Pump-Turbine at Runaway: Rigid and Elastic Water Column Oscillation Modes  

    Nicolet, Christophe (Power Vision Engineering sarl, 1 ch. des Champs-Courbes ) , Alligne, Sebastien (Laboratory for Hydraulic Machines, Ecole Polytechnique Federale de Lausanne, EPFL ) , Kawkabani, Basile (Laboratory of Electrical Machines, Ecole Polytechnique Federale de Lausanne, EPFL ) , Simond, Jean-Jacques (Laboratory of Electrical Machines, Ecole Polytechnique Federale de Lausanne, EPFL ) , Avellan, Francois (Laboratory for Hydraulic Machines, Ecole Polytechnique Federale de Lausanne, EPFL)
    International journal of fluid machinery and systems v.2 no.4 ,pp. 324 - 333 , 2009 ,

    초록

    This paper presents a numerical simulation study of the transient behavior of a $2{\times}340MW$ pump-turbine power plant, where the results show an unstable behavior at runaway. First, the modeling of hydraulic components based on equivalent schemes is presented. Then, the 2 pump-turbine test case is presented. The transient behavior of the power plant is simulated for a case of emergency shutdown with servomotor failure on Unit 1. Unstable operation at runaway with a period of 15 seconds is properly simulated using a 1-dimensional approach. The simulation results points out a switch after 200 seconds of the unstable behavior between a period of oscillations initially of 15 seconds to a period of oscillation of 2.16 seconds corresponding to the hydraulic circuit first natural period. The pressure fluctuations related to both the rigid and elastic water column mode are presented for oscillation mode characterization. This phenomenon is described as a switch between a rigid and an elastic water column oscillation mode. The influence of the rotating inertia on the switch phenomenon is investigated through a parametric study.

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  8. [국내논문]   Dynamic Simulation of Pump-Storage Power Plants with different variable speed configurations using the Simsen Tool  

    Kruger, Klaus (Voith Hydro Holding GmbH & Co. KG ) , Koutnik, Jiri (Voith Hydro Holding GmbH & Co. KG)
    International journal of fluid machinery and systems v.2 no.4 ,pp. 334 - 345 , 2009 ,

    초록

    Pumped storage power plants are playing a significant role in the contribution to the stabilization of an electrical grid, above all by stable operation and fast reaction to sudden load respectively frequency changes. Optimized efficiency and smooth running characteristics both in pump and turbine operation, improved stability for synchronization in turbine mode, load control in pump mode operation and also short reaction times may be achieved using adjustable speed power units. Such variable speed power plants are applicable for high variations of head (e.g. important for low head pump-turbine projects). Due to the rapid development of power semiconductors and frequency converter technology, feasible solutions can be provided even for large hydro power units. Suitable control strategies as well as clear design criteria contribute significantly to the optimal usage of the pump turbine and motor-generators. The SIMSEN tool for dynamic simulations has been used for comparative investigations of different configurations regarding the power converter topology, types of semiconductors and types of motor-generators including the coupling to the hydraulic system. A brief overview of the advantages & disadvantages of the different solutions can also be found in this paper. Using this approach, a customized solution minimizing cost and exploiting the maximum usage of the pump-turbine unit can be developed in the planning stage of new and modernization pump storage projects.

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  9. [국내논문]   Large Eddy Simulation of a High Reynolds Number Swirling Flow in a Conical Diffuser  

    Duprat, Cedric (LEGI INPG CNRS - Modelisation et Simulation de la Turbulence (MoST) ) , Metais, Olivier (LEGI INPG CNRS - Modelisation et Simulation de la Turbulence (MoST) ) , Laverne, Thomas (Alstom HYDRO FRANCE)
    International journal of fluid machinery and systems v.2 no.4 ,pp. 346 - 352 , 2009 ,

    초록

    The objective of the present work is to improve numerical predictions of unsteady turbulent swirling flows in the draft tubes of hydraulic power plants. We present Large Eddy Simulation (LES) results on a simplified draft tube consisting of a straight conical diffuser. The basis of LES is to solve the large scales of motion, which contain most of the energy, while the small scales are modeled. LES strategy is here preferred to the average equations strategies (RANS models) because it resolves directly the most energetic part of the turbulent flow. LES is now recognized as a powerful tool to simulate real applications in several engineering fields which are more and more frequently found. However, the cost of large-eddy simulations of wall bounded flows is still expensive. Bypass methods are investigated to perform high-Reynolds-number LES at a reasonable cost. In this study, computations at a Reynolds number about 2 $10^5$ are presented. This study presents the result of a new near-wall model for turbulent boundary layer taking into account the streamwise pressure gradient (adverse or favorable). Validations are made based on simple channel flow, without any pressure gradient and on the data base ERCOFTAC. The experiments carried out by Clausen et al. [1] reproduce the essential features of the complex flow and are used to develop and test closure models for such flows.

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  10. [국내논문]   Surface Roughness Impact on Francis Turbine Performances and Prediction of Efficiency Step Up   피인용횟수: 1

    Maruzewski, Pierre (Ecole polytechnique federale de Lausanne, Laboratory of Hydraulic Machines ) , Hasmatuchi, Vlad (Ecole polytechnique federale de Lausanne, Laboratory of Hydraulic Machines ) , Mombelli, Henri-Pascal (Ecole polytechnique federale de Lausanne, Laboratory of Hydraulic Machines ) , Burggraeve, Danny (British Columbia Hydro Generating Engineering Country ) , Iosfin, Jacob (British Columbia Hydro Generating Engineering Country ) , Finnegan, Peter (British Columbia Hydro Generating Engineering Country ) , Avellan, Francois (Ecole polytechnique federale de Lausanne, Laboratory of Hydraulic Machines)
    International journal of fluid machinery and systems v.2 no.4 ,pp. 353 - 362 , 2009 ,

    초록

    In the process of turbine modernizations, the investigation of the influences of water passage roughness on radial flow machine performance is crucial and validates the efficiency step up between reduced scale model and prototype. This study presents the specific losses per component of a Francis turbine, which are estimated by CFD simulation. Simulations are performed for different water passage surface roughness heights, which represents the equivalent sand grain roughness height. As a result, the boundary layer logarithmic velocity profile still exists for rough walls, but moves closer to the wall. Consequently, the wall friction depends not only on roughness height but also on its shape and distribution. The specific losses are determined by CFD numerical simulations for each component of the prototype, taking into account its own specific sand grain roughness height. The model efficiency step up between reduced scale model and prototype value is finally computed by the assessment of specific losses on prototype and by evaluating specific losses for a reduced scale model with smooth walls. Furthermore, surveys of rough walls of each component were performed during the geometry recovery on the prototype and comparisons are made with experimental data from the EPFL Laboratory for Hydraulic Machines reduced scale model measurements. This study underlines that if rough walls are considered, the CFD approach estimates well the local friction loss coefficient. It is clear that by considering sand grain roughness heights in CFD simulations, its forms a significant part of the global performance estimation. The availability of the efficiency field measurements provides an unique opportunity to assess the CFD method in view of a systematic approach for turbine modernization step up evaluation. Moreover, this paper states that CFD is a very promising tool for future evaluation of turbine performance transposition from the scale model to the prototype.

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논문관련 이미지