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  • 1
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    Photophoretic force on microparticles in complex plasmas (2017)
    Institute of Physics (IOP)
    Details
    Publication Date: 2017-07-11
    Description: Experimental observations are presented of unusual (‘abnormal’) microparticles, having trajectories very different from those of the majority of microparticles in the particle cloud in PK-3 Plus chamber (on board the International Space Station). To quantitatively study the mechanism driving this ‘irregular’ motion, we performed a series of experiments with quasi-two-dimensional complex plasmas in a modified GEC RF reference cell in a ground-based laboratory. The results show that the average particle velocity increases with illumination laser power, particularly for the ‘abnormal’ particles. We suggest that the photophoretic force provides an important contribution to the drive, and briefly discuss the mechanism leading to this effect. Optical microscopy results indicate that the ‘abnormal’ particles could be those having deformations or defects on their surface.
    Electronic ISSN: 1367-2630
    Topics: Physics
    Published by Institute of Physics (IOP)
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  • 2
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    On the physical mechanisms governing self-excited pressure surge in Francis turbines (2014)
    Institute of Physics (IOP)
    Details
    Publication Date: 2014-12-11
    Description: The required operating range for hydraulic machines is continually extended in an effort to integrate renewable energy sources with unsteady power outputs into the existing electrical grid. The off-design operation however brings forth unfavorable flow patterns in the machine, causing dynamic problems involving cavitation, which may represent a limiting factor to the energy production. In Francis turbines it is observed that the self-excited oscillation of a vortex rope in the draft tube cone prevents the delivery of maximum power when required. This phenomenon is referred to as full load pressure surge and has been the object of extensive research during the past decades. Several contributions deepened its understanding through measurement and simulation of the local flow properties and the global stability parameters. The draft tube pressure level and the runner outlet swirl are identified as key variables in the modelling of the vortex rope dynamics. Recently, a cyclic appear...
    Print ISSN: 1755-1307
    Electronic ISSN: 1755-1315
    Topics: Geography , Geosciences , Physics
    Published by Institute of Physics (IOP)
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  • 3
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    Pressure measurements and high speed visualizations of the cavitation phenomena at deep part load condition in a Francis turbine (2014)
    Institute of Physics (IOP)
    Details
    Publication Date: 2014-12-11
    Description: In a hydraulic power plant, it is essential to provide a reliable, sustainable and flexible energy supply. In recent years, in order to cover the variations of the renewable electricity production, hydraulic power plants are demanded to operate with more extended operating range. Under these off-design conditions, a hydraulic turbine is subject to cavitating swirl flow at the runner outlet. It is well-known that the helically/symmetrically shaped cavitation develops at the runner outlet in part load/full load condition, and it gives severe damage to the hydraulic systems under certain conditions. Although there have been many studies about partial and full load conditions, contributions reporting the deep part load condition are limited, and the cavitation behaviour at this condition is not yet understood. This study aims to unveil the cavitation phenomena at deep part load condition by high speed visualizations focusing on the draft tube cone as well as the runner blade channel...
    Print ISSN: 1755-1307
    Electronic ISSN: 1755-1315
    Topics: Geography , Geosciences , Physics
    Published by Institute of Physics (IOP)
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  • 4
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    Numerical and experimental evidence of the inter-blade cavitation vortex development at deep part load operation of a Francis turbine (2016)
    Institute of Physics (IOP)
    Details
    Publication Date: 2016-12-13
    Description: Francis turbines are subject to various types of the cavitation flow depending on the operating conditions. In order to compensate for the stochastic nature of renewable energy sources, it is more and more required to extend the operating range of the generating units, from deep part load to full load conditions. In the deep part load condition, the formation of cavitation vortices in the turbine blade to blade channels called inter-blade cavitation vortex is often observed. The understanding of the dynamic characteristics of these inter-blade vortices and their formation mechanisms is of key importance in an effort of developing reliable flow simulation tools. This paper reports the numerical and experimental investigations carried out in order to establish the vortex characteristics, especially the inception and the development of the vortex structure. The unsteady RANS simulation for the multiphase flow is performed with the SST- SAS turbulence model by using the commercial f...
    Print ISSN: 1755-1307
    Electronic ISSN: 1755-1315
    Topics: Geography , Geosciences , Physics
    Published by Institute of Physics (IOP)
    Location Call Number Limitation Availability
    BibTip Others were also interested in ...
    PAPER CURRENT
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