Topic
Rotational speed
About: Rotational speed is a research topic. Over the lifetime, 23327 publications have been published within this topic receiving 151696 citations. The topic is also known as: speed of revolution & revolution rate.
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01 Aug 2010TL;DR: In this article, an experimental investigation focusing on the upper part load vortex rope was performed on a high specific speed Francis turbine scale model installed on a test rig of the EPFL Laboratory for Hydraulic Machines.
Abstract: The swirling flow developing in Francis turbine draft tube under part load operation leads to pressure fluctuations usually in the range of 0.2 to 0.4 times the runner rotational frequency resulting from the so-called vortex breakdown. For low cavitation number, the flow features a cavitation vortex rope animated with precession motion. Under given conditions, these pressure fluctuations may lead to undesirable pressure fluctuations in the entire hydraulic system and also produce active power oscillations. For the upper part load range, between 0.7 and 0.85 times the best efficiency discharge, pressure fluctuations may appear in a higher frequency range of 2 to 4 times the runner rotational speed and feature modulations with vortex rope precession. It has been pointed out that for this particular operating point, the vortex rope features elliptical cross section and is animated of a self-rotation. This paper presents an experimental investigation focusing on this peculiar phenomenon, defined as the upper part load vortex rope. The experimental investigation is carried out on a high specific speed Francis turbine scale model installed on a test rig of the EPFL Laboratory for Hydraulic Machines. The selected operating point corresponds to a discharge of 0.83 times the best efficiency discharge. Observations of the cavitation vortex carried out with high speed camera have been recorded and synchronized with pressure fluctuations measurements at the draft tube cone. First, the vortex rope self rotation frequency is evidenced and the related frequency is deduced. Then, the influence of the sigma cavitation number on vortex rope shape and pressure fluctuations is presented. The waterfall diagram of the pressure fluctuations evidences resonance effects with the hydraulic circuit. The time evolution of the vortex rope volume is compared with pressure fluctuations time evolution using image processing. Finally, the influence of the Froude number on the vortex rope shape and the associated pressure fluctuations is analyzed by varying the rotational speed.
33 citations
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05 Jun 2014TL;DR: In this paper, a system comprising a discharge valve that allows some of the fluid generated by a fluid generating source and intended for a drive torque generating member for a rotary element of a mechanical device to be removed so as to limit the corresponding rotational speed is described.
Abstract: A system comprising a discharge valve that allows some of the fluid generated by a fluid generating source and intended for a drive torque generating member for a rotary element of a mechanical device to be removed so as to limit the corresponding rotational speed, this being done for a length of time that allows a thermal gradient to be reduced sufficiently that a phenomenon of deformation of said rotary element can be prevented.
33 citations
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TL;DR: In this paper, an experimental investigation of the influence of the applied static load and rotational speed on the behavior of a 160mm diameter cylindrical journal bearing with two axial grooves was conducted.
33 citations
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31 Jan 1994
TL;DR: A squirrel cage rotor for a high speed electric motor comprises longitudinally extending bars which are in electrical contact with, but not affixed to, conductive end rings of the rotor.
Abstract: A squirrel cage type rotor for a high speed electric motor comprises longitudinally extending bars which are in electrical contact with, but not affixed to, conductive end rings of the rotor. The bars are electrically conductive and are each affixed to the armature core at a single point located intermediate the end rings.
33 citations
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TL;DR: In this article, a study has been made to ascertain the mechanisms governing power consumption and to determine the influence of design and operating conditions on its magnitude in scraped-surface heat exchangers.
33 citations