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  • 1
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    Prediction of pressure fluctuation of a hydraulic turbine at no-load condition (2015)
    Institute of Physics (IOP)
    Details
    Publication Date: 2015-01-16
    Description: In order to study characteristics of pressure fluctuation of a turbine during the starting period, a turbine with guide vanes device at no-load condition was investigated using RNG k- ##IMG## [http://ej.iop.org/icons/Entities/epsilon.gif] {epsilon} turbulence model. The inner flow distribution and pressure fluctuation characteristics were analyzed. Results show that the pressure fluctuations in the region between the runner and guide vanes are different around the runner inlet. The dominant frequency of pressure fluctuation in the vaneless space close to the casing outlet is the blade passing frequency, while the dominant frequency at the rest region is the twice of the blade passing frequency. The increase of amplitude of pressure fluctuation close to the casing outlet can be attribute to the large scale stall at suction side of the runner inlet.
    Print ISSN: 1757-8981
    Electronic ISSN: 1757-899X
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
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  • 2
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    Numerical investigation of performance of vane-type propellant management device by VOF methods (2015)
    Institute of Physics (IOP)
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    Publication Date: 2015-01-16
    Description: The orbital propellant management performance of the vane-type tank is so important for the propellant system and it determines the lifetime of the satellite. The propellant in the tank can be extruded by helium gas. To study the two phase distribution in the vane-type surface tension tank and the capability of the vane-type propellant management device (PMD), a large volume vane-type surface tension tank is analysed using 3-D unsteady numerical simulations. VOF methods are used to analyse the location of the interface of the two phase. Performances of the propellant acquisition vanes and propellant refillable reservoir in the tank are investigated. The flow conductivity of the propellant acquisition vanes and the liquid storage capacity of propellant refillable reservoir can be affected by the value of the gravity and the volume of the propellant in the tank. To avoid the large resistance causing by surface tension in an outflow of a small hole, the design of the vanes in a pro...
    Print ISSN: 1757-8981
    Electronic ISSN: 1757-899X
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
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  • 3
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    Pressure fluctuation prediction of a model pump turbine at no load opening by a nonlinear k-ε turbulence model (2014)
    Institute of Physics (IOP)
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    Publication Date: 2014-12-11
    Description: In this paper, a new nonlinear k-ε turbulence model based on RNG k-ε turbulence model and Wilcox's k - ω turbulence model was proposed to simulate the unsteady flow and to predict the pressure fluctuation through a model pump turbine for engineering application. Calculations on a curved rectangular duct proved that the nonlinear k - ε turbulence model is applicable for high pressure gradient flows and large curvature flows. The numerically predicted relative pressure amplitude (peak to peak) in time domain to the pump turbine head at no load condition is very close to the experimental data. It is indicated that the prediction of the pressure fluctuation is valid by the present nonlinear k-ε method. The high pressure fluctuation in this area is the main issue for pump turbine design, especially at high head condition.
    Print ISSN: 1755-1307
    Electronic ISSN: 1755-1315
    Topics: Geography , Geosciences , Physics
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  • 4
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    Numerical study of pressure fluctuations transfer law in different flow rate of turbine mode in a prototype pump turbine (2013)
    Institute of Physics (IOP)
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    Publication Date: 2013-12-22
    Description: Numerical simulation using SST k-w turbulence model was carried out, to predict pressure fluctuation transfer law in turbine mode. Three operating points with different mass flow rates are simulated. The results of numerical simulation show that, the amplitude and frequency of pressure fluctuations in different positions are very different. The transfer law of amplitude and frequency of pressure fluctuations change with different position and different mass flow rate. Blade passing frequency (BPF) is the first dominant frequency in vaneless space, while component in this frequency got smaller in the upstream and downstream of vaneless space when the mass flow is set. Furthermore triple blade passing frequency (3BPF) component obtained a different transfer law through the whole flow passage. The amplitude and frequency of pressure fluctuations is also different in different circumference position of vaneless space. When the mass flow is different, the distribution of pressure flu...
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    Electronic ISSN: 1757-899X
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
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  • 5
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    Prediction of cavitation performance of a hydrofoil in water at high temperatures (2013)
    Institute of Physics (IOP)
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    Publication Date: 2013-12-22
    Description: In this paper, the thermodynamic effects of cavitation based on the computational methodology of cavitation mass transfer has been considered in the prediction of cavitation performance of a hydrofoil in water at high temperature. A cavitation mass transfer model to study this phenomenon has been presented. The cavitation model was used to simulate the flow along a NACA0015 hydrofoil at different temperatures. The results were compared with experiments. From the distribution of the pressure coefficient, it can be seen that the simulation results with the improved model have the same trends and values comparing with the experiments. At low temperature, the length of the cavity area is nearly the same with experiment, but at high temperature, the calculated cavity length is slightly longer.
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    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
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  • 6
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    Numerical analysis of unsteady cavitation shedding dynamics around NACA66 hydrofoil by large-eddy simulation (2013)
    Institute of Physics (IOP)
    Details
    Publication Date: 2013-12-22
    Description: Large-Eddy simulation (LES) coupling with mass transfer cavitation model was used to resolve the turbulent flow structure with cavitation. The results will focus on the cavitation shedding dynamics around NACA66 hydrofoil. The predicted results compare well with the experimental measurements for steady/unsteady partial cavitating flows. Numerical visualizations of cloud cavity evolution and surface pressure signals show relatively good agreement with the experimental data.
    Print ISSN: 1757-8981
    Electronic ISSN: 1757-899X
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
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  • 7
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    Numerical evaluations of the effect of leading-edge protuberances on the static and dynamic stall characteristics of an airfoil (2013)
    Institute of Physics (IOP)
    Details
    Publication Date: 2013-12-22
    Description: Wavy leading edge modifications of airfoils through imitating humpback whale flippers has been considered as a viable passive way to control flow separation. In this paper, flows around a baseline 63 4 -021 airfoil and one with leading-edge sinusoidal protuberances were simulated using S-A turbulence model. When studying the static stall characteristics, it is found that the modified airfoil does not stall in the traditional manner, with increasing poststall lift coefficients. At high angles of attack, the flows past the wavy leading edge stayed attached for a distance, while the baseline foil is in a totally separated flow condition. On this basis, the simulations of pitch characteristic were carried out for both foils. At high angles of attack mild variations in lift and drag coefficients of the modified foil can be found, leading to a smaller area of hysteresis loop. The special structure of wavy leading edge can help maintain high consistency of the flow field in dy...
    Print ISSN: 1757-8981
    Electronic ISSN: 1757-899X
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
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  • 8
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    3-D Simulation of a prototype pump-turbine during starting period in turbine model (2013)
    Institute of Physics (IOP)
    Details
    Publication Date: 2013-12-22
    Description: Three dimensional (3-D), unsteady flows in a prototype pump-turbine during a transient process of start-up at no load condition were studied using the computational fluid dynamics method. The fluid coupling and DM method were used to calculate the rotational speed for each time step. The dynamic mesh (DM) method and remeshing method were applied to simulate the rotation of guide vanes. Calculations were performed based on the ##IMG## [http://ej.iop.org/icons/Entities/barv.gif] {bar v} 2 − f turbulence model, and the calculation results were compared and verified by experimental data. Transient explicit characteristics such as the flow-rate, head, torque of the runner etc., as well as the internal flow during the start-up were analyzed. The amplitude of pressure fluctuation was larger as the rotational speed of runner increased. The pump-turbine was more unstable with the decrease of th...
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    Electronic ISSN: 1757-899X
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
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  • 9
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    A new nonlinear turbulence model based on Partially-Averaged Navier-Stokes Equations (2013)
    Institute of Physics (IOP)
    Details
    Publication Date: 2013-12-22
    Description: Partially-averaged Navier-Stokes (PANS) Model was recognized as a Reynolds-averaged Navier-Stokes (RANS) to direct numerical simulation (DNS) bridging method. PANS model was purported for any filter width-from RANS to DNS. PANS method also shared some similarities with the currently popular URANS (unsteady RANS) method. In this paper, a new PANS model was proposed, which was based on RNG k-ε turbulence model. The Standard and RNG k-ε turbulence model were both isotropic models, as well as PANS models. The sheer stress in those PANS models was solved by linear equation. The linear hypothesis was not accurate in the simulation of complex flow, such as stall phenomenon. The sheer stress here was solved by nonlinear method proposed by Ehrhard. Then, the nonlinear PANS model was set up. The pressure coefficient of the suction side of the NACA0015 hydrofoil was predicted. The result of pressure coefficient agrees well with experimental result, which proves that the nonlinear PANS mode...
    Print ISSN: 1757-8981
    Electronic ISSN: 1757-899X
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
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  • 10
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    Study of unsteady cavitation flow of a pump-turbine at pump mode (2013)
    Institute of Physics (IOP)
    Details
    Publication Date: 2013-12-22
    Description: Three dimensional, unsteady, cavitating flows in a pump-turbine at pump mode were numerically studied using SST k - ω turbulence model and the mixture model. The unsteady cavitating flow and pressure fluctuations at different positions were analysed with two openings of guide vanes. Calculation results are in good agreement with experimental data. Results show that the opening of guide vanes has great effect on the cavitation phenomenon. The cavitating region gradually decreases with the increase of the relative opening, and it locates at the inlet of the suction side. The amplitude of the pressure fluctuation reduces as the cavitating region decreases. The numerical study of unsteady cavitating flow can provide a basic understanding for the improvement of stable operation of a pump-turbine.
    Print ISSN: 1757-8981
    Electronic ISSN: 1757-899X
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
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