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 C p at 63% axial chord on the suction surface. Data were taken at Re c =20 K with 3% inlet freestream turbulence and a wake-passing flow coefficient of 0.8. Without unsteady wakes, a nonreattaching 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 C p and phase-locked velocity measurements confirm that the optimal combination of wakes and jets yields the smallest separation.