| 1. |
- Karlsson, Martin, et al.
(author)
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Influence of inlet boundary conditions in the prediction of rotor dynamic forces and moments for a hydraulic turbine using CFD
- 2008
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In: ISROMAC-12. - Honolulu.
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Conference paper (peer-reviewed)abstract
- The rotordynamic behavior of a hydraulic turbine is influenced by fluid-rotor interactions at the turbine runner. In this paper computational fluid dynamics (CFD) is used to numerically predict the rotordynamical excitation forces due to the flow through a hydraulic turbine runner. The simulations are carried out for three different boundary conditions. One axi-symmetric inlet boundary condition, and two axi-periodic boundary conditions. The two latter are obtained from separate simulations of wicket gate and spiral casing flow. It is found that the inlet boundary condition significantly affects the rotordynamical forces and moments.
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| 2. |
- Karlsson, Martin, et al.
(author)
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Numerical estimation of torsional dynamic coefficients of a hydraulic turbine
- 2009
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In: International Journal of Rotating Machinery. - : Hindawi Limited. - 1023-621X .- 1542-3034.
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Journal article (peer-reviewed)abstract
- The rotordynamic behavior of a hydraulic turbine is influenced by fluid-rotor interactions at the turbine runner. In this paper computational fluid dynamics (CFDs) are used to numerically predict the torsional dynamic coefficients due to added polar inertia, damping, and stiffness of a Kaplan turbine runner. The simulations are carried out for three operating conditions, one at about 35% load, one at about 60% load (near best efficiency), and one at about 70% load. The runner rotational speed is perturbed with a sinusoidal function with different frequencies in order to estimate the coefficients of added polar inertia and damping. It is shown that the added coefficients are dependent of the load and the oscillation frequency of the runner. This affect the system's eigenfrequencies and damping. The eigenfrequency is reduced with up to 65% compared to the eigenfrequency of the mechanical system without the fluid interaction. The contribution to the damping ratio varies between 30-80% depending on the load. Hence, it is important to consider these added coefficients while carrying out dynamic analysis of the mechanical system.
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| 3. |
- Muntean, S., et al.
(author)
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Mathematical, numerical and experimental analysis of the swirling flow at a Kaplan runner outlet
- 2012
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In: 26th IAHR Symposium on Hydraulic Machinery and Systems. - : IOP Publishing Ltd. ; 15:Part 3, s. Art. no. 032001-
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Conference paper (peer-reviewed)abstract
- The paper presents a novel mathematical model for a-priori computation of the swirling flow at Kaplan runners outlet. The model is an extension of the initial version developed by Susan-Resiga et al [1], to include the contributions of non-negligible radial velocity and of the variable rothalpy. Simple analytical expressions are derived for these additional data from three-dimensional numerical simulations of the Kaplan turbine. The final results, i.e. velocity components profiles, are validated against experimental data at two operating points, with the same Kaplan runner blades opening, but variable discharge
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| 4. |
- Nilsson, Håkan, 1971, et al.
(author)
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Effects of inlet boundary conditions, on the computed flow in the Turbine-99 draft tube, using OpenFOAM and CFX
- 2012
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In: 26th IAHR Symposium on Hydraulic Machinery and Systems. - : IOP Publishing Ltd. ; 15:PART 3, s. Art. no. 032002-
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Conference paper (peer-reviewed)abstract
- The flow in the Turbine-99 Kaplan draft tube was thoroughly investigated at three workshops (1999, 2001, 2005), which aimed at determining the state of the art of draft tube simulations. The flow is challenging due to the different flow phenomena appearing simultaneously such as unsteadiness, separation, swirl, turbulence, and a strong adverse pressure gradient. The geometry and the experimentally determined inlet boundary conditions were provided to the Turbine-99 workshop participants. At the final workshop, angular resolved inlet velocity boundary conditions were provided. The rotating non-axi-symmetry of the inlet flow due to the runner blades was thus included. The effect of the rotating angular resolution was however not fully investigated at that workshop. The first purpose of this work is to further investigate this effect. Several different inlet boundary conditions are applied – the angular resolved experimental data distributed at the Turbine-99 workshop, the angular resolved results of a runner simulation with interpolated values using different resolution in the tangential and radial directions, and an axi-symmetric variant of the same numerical data. The second purpose of this work is to compare the results from the OpenFOAM and CFX CFD codes, using as similar settings as possible. The present results suggest that the experimental angular inlet boundary conditions proposed to the workshop are not adequate to simulate accurately the flow in the T-99 draft tube. The reason for this is that the experimental phase-averaged data has some important differences compared to the previously measured time-averaged data. Using the interpolated data from the runner simulation as inlet boundary condition however gives good results as long as the resolution of that data is sufficient. It is shown that the difference between the results using the angular-resolved and the corresponding symmetric inlet data is very small, suggesting that the importance of the angular resolution is small. The results from OpenFOAM and CFX are very similar as long as the inlet data resolution is fine enough. CFX seems to be more sensitive to that resolution.
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| 5. |
- Petit, Olivier, 1980, et al.
(author)
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Comparison of numerical and experimental results of the flow in the U9 Kaplan turbine model
- 2010
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In: 25th IAHR Symposium on Hydraulic Machinery and Systems. - London : IOP Publishing Ltd. ; , s. 12024-
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Conference paper (peer-reviewed)abstract
- The present work compares simulations made using the OpenFOAM CFD code with experimental measurements of the flow in the U9 Kaplan turbine model. Comparisons of the velocity profiles in the spiral casing and in the draft tube are presented. The U9 Kaplan turbine prototype located in Porjus and its model, located in Älvkarleby, Sweden, have curved inlet pipes that lead the flow to the spiral casing. Nowadays, this curved pipe and its effect on the flow in the turbine is not taken into account when numerical simulations are performed at design stage. To study the impact of the inlet pipe curvature on the flow in the turbine, and to get a better overview of the flow of the whole system, measurements were made on the 1:3.1 model of the U9 turbine. Previously published measurements were taken at the inlet of the spiral casing and just before the guide vanes, using the laser Doppler anemometry (LDA) technique. In the draft tube, a number of velocity profiles were measured using the LDA techniques. The present work extends the experimental investigation with a horizontal section at the inlet of the draft tube. The experimental results are used to specify the inlet boundary condition for the numerical simulations in the draft tube, and to validate the computational results in both the spiral casing and the draft tube. The numerical simulations were realized using the standard k-e model and a block-structured hexahedral wall function mesh.
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| 6. |
- Petit, Olivier, 1980, et al.
(author)
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Numerical and experimental investigations of a hydraulic pipe during a gate closure at high Reynolds number
- 2015
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In: 6th IAHR meeting of the Working Group Cavitation and dynamic problems. - : Faculty of technologies and systems.
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Conference paper (peer-reviewed)abstract
- The role of hydropower to provide regulated power is important to the Swedish power system. This becomes even more accentuated with the expansion of intermittent renewable electricity sources, such as wind power. The variation of hydropower operation ranges over a large spectrum of time scales, from seconds to years. For scales larger than a minute, the flow may be considered as quasi-steady from a hydrodynamic point of view. The present work addresses the shorter time scales. Such scales are manifested mainly as pressure transients, which is an issue of concern in design and operation of hydropower plants.The objective of the study is to address rapid pressure transients with a special focus on detailed 3D processes interacting with transients travelling in an essentially 1D geometry. The test case is a gate closing in a long rectangular pipe, where a high-Reynolds number flow is driven by a pressure difference between upper and lower water levels. Experimental time-resolved static pressure and PIV data are gathered for validation of the numerical results.In a first stage the computational domain is modelled in 3D with an incompressible volume of fluid method that includes the prediction of the free surfaces. The domain includes the upper and lower water tanks with free water surfaces, a pipe in-between and a closing and opening gate. The gate movement is modelled with a dynamic mesh that removes the cells as the gate closes. The block-structured mesh is generated in ICEM CFD, and parallel simulations are performed using the OpenFOAM open source software. The numerical results are compared with the experimental data, and it is shown that the experimentally observed pressure fluctuations after gate closure are not an effect of the free surfaces.In a second stage, the upper tank and the pipe are modelled using a compressible 1D code based on the method of characteristics (MOC). A comparison with the experimental data shows that the correct unsteady behavior of the system is captured by the 1D approach if the losses and the gate characteristics are correctly accounted for, at the same time as the compressibility is adapted to the air contents of the water and flexibility of the structure.
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