A tip-leakage vortex periodically disturbed by upstream vortical inflow is studied in a cascade facility. The object of this paper is an improved understanding of the time-resolved scale and form of the coherent structures of the tip-leakage flow, especially the aperiodic motion of the coherent turbulence structure within the tip-leakage vortex, which dominates the turbulence kinetic energy. This information is relevant to the understanding and prediction of broadband tip-leakage noise by the rotor blades and intermittent cavitation in propulsion pumps. The cascade facility has a moving endwall on which vortex-generator pairs are attached upstream of the blade row to generate an unsteady periodic vortical inflow representative of an array of stator necklace vortices. The downstream tip-leakage vortex is disturbed periodically by the vortical inflow shed by those vortex generators. Phase-averaged two-point correlations are measured near the trailing edge of the cascade. The measurement results clearly show that organized, intense, large-scale aperiodic motion exists at each phase time within the tip-leakage-vortex region. The aperiodic fluctuations obtained by linear stochastic estimation have a magnitude of less than plus or minus 0.15 U in all three velocity directions and appear to be organized large-scale structures. The streamwise fluctuations appear as coexisting 'rush' and 'retard' regions with different shapes, and the crossflow fluctuations appear to be clockwise/ anticlockwise or doubletlike rotating vortical structures with different strengths and center positions. These aperiodic fluctuations make the estimated instantaneous velocity field significantly different from the phase-averaged periodic velocity field.
Unsteady aperiodic behavior of a periodically disturbed tip-leakage vortex
Unstetig-aperiodisches Verhalten eines periodisch gestörten Spaltverlust-Wirbels
AIAA Journal ; 46 , 5 ; 1025-1038
2008
14 Seiten, 12 Bilder, 2 Tabellen, 9 Quellen
Article (Journal)
English
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