Unsteady Aperiodic Behavior of a Periodically Disturbed Tip-Leakage Vortex

Abstract

unsteadyperiodicvorticalinflow representativeof anarrayofstator necklace vortices.Thedownstream 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 � 0:15U1 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 phaseaveraged periodic velocity field.