Synchronizing Separation Flow Control With Unsteady Wakes in a Low-Pressure Turbine Cascade

Particle image velocimetry (PIV) measurements were made on a highly loaded low-pressure turbine blade in a linear cascade. The Pack B blade has a design Zweifel coefficient of 1.15 and a peak Cp at 63% axial chord on the suction surface. Data were taken at Re_c = 20K with 3% inlet freestream turbulence and a wake passing flow coefficient of 0.8. Without unsteady wakes, a non-reattaching separation bubble exists on the suction surface of the blade beginning at 68% axial chord. The time averaged separation zone is reduced in size by approximately 35% in the presence of unsteady wakes. Phase-locked hot-wire and PIV measurements were used to document the dynamics of this separation zone when subjected to synchronized, unsteady forcing from a spanwise row of vortex generator jets (VGJs) in addition to the unsteady wakes. The phase difference between VGJ actuation and the wake passing was optimized. Both steady state Cp and phase-locked velocity measurements confirm that the optimal combination of wakes and jets yields the smallest separation.