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Mitigation Of Pressure Fluctuations În A Conical Diffuser With Precessing Vortex Rope Using Axial Jet Control Method
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Proceedings of the 24th IAHR Symposium on Hydraulic Machinery and Systems, Foz do Iguassu, Paper #80, ISBN: 978-85-60858-13-1, Brazilia, Oct.
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ABSTRACT
Operating Francis turbines at partial discharge is often hindered by the development of the
helical vortex (so-called vortex rope) downstream the runner, in the draft tube cone. The unsteady
pressure field induced by the precessing vortex rope leading to pressure fluctuations. In this paper a
simple and robust method to mitigate the vortex rope by using an axial water jet is evaluated. The
vortex rope mitigation using jet control method is investigated experimentally on the test rig
developed at the Politehnica University of Timisoara (UPT) – National Center for Engineering
Systems with Complex Fluids (NCESCF). The swirling flow with precessing vortex rope is
developed in test section of the test rig. The unsteady pressure is measured with two transducers
flush mounted on the conical diffuser wall of the test section. The Fourier spectra of the unsteady
pressure measured in S1 and S2 sections are obtained without and with axial jet control. The
pressure recovery coefficient and relative root-means-square pressure fluctuation coefficient are
computed in order to evaluate the jet control method. Consequently, the pressure fluctuation on
cone wall associated with the precessing vortex rope are mittigated or completely eliminated.
According to our experimental investigations a 10% jet discharge is required in order to operate
with maximum pressure recovery and without pressure fluctuations. As a result, in order to
efficiently apply the jet control technique to hydraulic turbines a flow-feedback approach must be
taken into account.
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2008
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| conical diffuser, swirling flow, precessing vortex rope, pressure fluctuation, axial jet control method |
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MUNTEAN Sebastian
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SUSAN-RESIGA Romeo
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BOSIOC Ilie Alin
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STUPARU Adrian
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BAYA Alexandru
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ANTON Liviu Eugen
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International Conference Proceedings
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http://acad-tim.tm.edu.ro/iSMART-flow/pdf/MunteanIAHR2008_Brazilia.pdf
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Numerical Simulation and Parallel Computing Laboratory
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UPT
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