Proper Orthogonal Decomposition of Pressure Fields in a Draft Tube Cone of the Francis (Tokke) Turbine Model

Štefan, David; Rudolf, Pavel

doi:10.1088/1742-6596/579/1/012002

Cited by 14 publications

(17 citation statements)

References 7 publications

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“…It means that the resulting vortex rope is wrapped around the low velocity zone, Fig.3. The corkscrew vortex in turbine diffuser is also called a precessing vortex core (PVC) due to its kinematics [1,2]. Precessing motion of the vortex rope is a source of pressure pulsations both in radial and axial direction.…”

Section: Vortex Rope In Hydraulic Turbine Diffusermentioning

confidence: 99%

Manipulation of the swirling flow instability in hydraulic turbine diffuser by different methods of water injection

et al. 2018

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Abstract. Vortex rope, which induces substantial pressure pulsations, arises in the draft tube (diffuser) of Francis turbine for off-design operating conditions. Present paper focuses on mitigation of those pulsations using active water jet injection control. Several modifications of the original Susan-Resiga's idea were proposed. All modifications are driven by manipulation of the shear layer region, which is believed to play important role in swirling flow instability. While some of the methods provide results close to the original one, none of them works in such a wide range. Series of numerical experiments support the idea that the necessary condition for vortex rope pulsation mitigation is increasing the fluid momentum along the draft tube axis.

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Section: Vortex Rope In Hydraulic Turbine Diffusermentioning

confidence: 99%

Manipulation of the swirling flow instability in hydraulic turbine diffuser by different methods of water injection

et al. 2018

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“…Comprehensive study of the cavitating spiral vortex within the elbow draft tube was done by Štefan et al [10]. The POD analysis of the HS video capturing cavitation cloud over NACA profile was done by Rudolf et al [11].…”

Section: Proper Orthogonal Decomposition Of the High Speed Recordsmentioning

confidence: 99%

Transition of cavitating flow to supercavitation within Venturi nozzle – hysteresis investigation

et al. 2017

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Abstract. Cavitation is usually considered as undesirable phenomena. On the other hand, it can be utilized in many applications. One of the technical applications is using cavitation in water treatment, where hydrodynamic cavitation seems to be effective way how to reduce cyanobacteria within large bulks of water. The main scope of this paper is investigation of the cavitation within Venturi nozzle during the transition from fully developed cavitation to supercavitation regime and vice versa. Dynamics of cavitation was investigated using experimental data of pressure pulsations and analysis of high speed videos, where FFT of the pixel intensity and Proper Orthogonal Decomposition (POD) of the records were done to identify dominant frequencies connected with the presence of cavitation. The methodology of the high speed (HS) records semiautomated analysis using the FFT was described. Obtained results were correlated and above that the possible presence of hysteresis was discussed.

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“…A non-linear harmonic technique was applied for the simulation and this technique is explained in Section 7, including their advantages and limitations. Spectral analysis and the obtained amplitude spectra at the three operating points, PL, BEP, and PL, are shown in Figures 17-19 [20]. A comparison of two difference codes, FLUENT and OpenFOAM, with the provided experimental data is conducted.…”

Section: Pressurementioning

confidence: 99%

“…Thus, the pressure amplitudes were found to be sensitive to the mesh density, time step sizing, turbulence modeling, discretization order, and boundary conditions [6, 8,9,11,13,16,20]. Spectral analysis and the obtained amplitude spectra at the three operating points, PL, BEP, and PL, are shown in Figures 17-19 [20]. A comparison of two difference codes, FLUENT and OpenFOAM, with the provided experimental data is conducted.…”

Section: Pressurementioning

confidence: 99%

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Experimental and Numerical Studies of a High-Head Francis Turbine: A Review of the Francis-99 Test Case

2016

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Hydraulic turbines are widely used to meet real-time electricity demands. Computational fluid dynamic (CFD) techniques have played an important role in the design and development of such turbines. The simulation of a complete turbine requires substantial computational resources. A specific approach that is applied to investigate the flow field of one turbine may not work for another turbine. A series of Francis-99 workshops have been planned to discuss and explore the CFD techniques applied within the field of hydropower with application to high-head Francis turbines. The first workshop was held in December 2014 at the Norwegian University of Science and Technology, Norway. The steady-state measurements were conducted on a model Francis turbine. Three operating points, part load, best efficiency point, and high load, were investigated. The complete geometry, meshing, and experimental data concerning the hydraulic efficiency, pressure, and velocity were provided to the academic and industrial research groups. Various researchers have conducted extensive numerical studies on the high-head Francis turbine, and the obtained results were presented during the workshop. This paper discusses the presented numerical results and the important outcome of the extensive numerical studies on the Francis turbine. The use of a wall function assuming equilibrium between the production and dissipation of turbulence is widely used in the simulation of hydraulic turbines. The boundary layer of hydraulic turbines is not fully developed because of the continuously-changing geometry and large pressure gradients. There is a need to develop wall functions that enable the estimation of viscous losses under boundary development for accurate simulations. Improved simulations and results enable reliable estimation of the blade loading. Numerical investigations on leakage flow through the labyrinth seals were conducted. The volumetric efficiency and losses in the seals were determined. The seal leakage losses formulated through analytical techniques are sufficient.

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Proper Orthogonal Decomposition of Pressure Fields in a Draft Tube Cone of the Francis (Tokke) Turbine Model

Cited by 14 publications

References 7 publications

Manipulation of the swirling flow instability in hydraulic turbine diffuser by different methods of water injection

Manipulation of the swirling flow instability in hydraulic turbine diffuser by different methods of water injection

Transition of cavitating flow to supercavitation within Venturi nozzle – hysteresis investigation

Experimental and Numerical Studies of a High-Head Francis Turbine: A Review of the Francis-99 Test Case

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