Measurements of the tip leakage vortex structures and turbulence in the meridional plane of an axial water-jet pump |
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Authors: | Huixuan Wu Rinaldo L Miorini Joseph Katz |
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Institution: | 1.Department of Mechanical Engineering,The Johns Hopkins University,Baltimore,USA;2.Department of Industrial Engineering,Università degli Studi di Bergamo,Dalmine,Italy |
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Abstract: | Particle image velocimetry (PIV) measurements at varying resolutions focus on the flow structures in the tip region of a water-jet
pump rotor, including the tip-clearance flow and the rollup process of a tip leakage vortex (TLV). Unobstructed views of these
regions are facilitated by matching the optical refractive index of the transparent pump with that of the fluid. High-magnification
data reveal the flow non-uniformities and associated turbulence within the tip gap. Instantaneous data and statistics of spatial
distributions and strength of vortices in the rotor passage reveal that the leakage flow emerges as a wall jet with a shear
layer containing a train of vortex filaments extending from the tip of the blade. These vortices are entrained into the TLV,
but do not have time to merge. TLV breakdown in the aft part of the blade passage further fragments these structures, increasing
their number and reducing their size. Analogy is made between the circumferential development of the TLV in the blade passage
and that of the starting jet vortex ring rollup. Subject to several assumptions, these flows display similar trends, including
conditions for TLV separation from the shear layer feeding vorticity into it. |
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Keywords: | |
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