Unsteady Periodic Behaviorof a Disturbed Tip-Leakage Flow

The unsteady periodic behavior of a tip-leakage flow downstream of a simulated axial compressor rotor has been studied. A linear cascade wind tunnel has been adapted to model this situation. The wind tunnel' features a moving endwall to simulate the relative motion between the rotor and casing and vortex generators attached to the moving end wall that produce an idealized periodic unsteady vortical inflow simulating the flow shed by the casing junctions of a row of inlet guide vanes. Detailed three-component mean-velocity and turbulence measurements have been made just downstream of the blade trailing edges and phase averaged with respect to the relative position of the blades and vortex generator wakes. The comparison between the disturbed and undisturbed tip-leakage flows shows that on time average the vortical inflow does not change the flowfield much, except for a slight decrease in streamwise velocity deficit and a small increase in turbulence kinetic energy in the tip-leakage vortex region. However, phase-averaged measurements reveal that the inflow vortices produce significant fluctuations in the size, strength, structure, and position of the tip-leakage vortex, despite the fact that they are about two orders weaker than the tip-leakage vortex. It is hypothesized that the unsteady vortical inflow influences the tip-leakage vortex at its formation, by periodically disturbing the shedding of vorticity from the blade tip.