Research Papers

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

[+] Author and Article Information
M. Bloxham, D. Reimann, K. Crapo, J. Pluim, J. P. Bons

Department of Mechanical Engineering, Brigham Young University, Provo, UT 84602

J. Turbomach 131(2), 021019 (Feb 03, 2009) (9 pages) doi:10.1115/1.2952376 History: Received August 14, 2007; Revised August 29, 2007; Published February 03, 2009

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 Rec=20K 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 Cp and phase-locked velocity measurements confirm that the optimal combination of wakes and jets yields the smallest separation.

Copyright © 2009 by American Society of Mechanical Engineers
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Figure 1

Three blade linear cascade

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Figure 2

VGJ exit velocity profile and data acquisition locations (PIV). VGJ orientation and coordinate system.

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Figure 3

CAD model of wake generator and test section of tunnel. Curved white arrows indicate direction of rotation. Straight arrow represents location of optical sensor.

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Figure 4

(a) The primary PIV configuration depicting both data regions. (b) The coordinate system used to present the data. Also included are the merged camera view fields, the axial chord lines of the Pack B, and a representation of the separation bubble.

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Figure 5

The in-plane PIV configuration. The green plane is a representation of the laser sheet.

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Figure 6

Experimental Cp distributions for the Pack B compared to the VBI. Plot includes no control (no wakes or jets), wake only, VGJ only, and combined wakes/jets data.

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Figure 7

Phase-locked isovelocity surfaces (U∕Uin=1.0) for wakes/jets (Case 6) configuration. The red arrows indicate approximate jet locations.

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Figure 8

Streamwise vorticity comparison for VGJs only (Case 3). VGJ at x∕d=0 and z∕d=9 (hole center). Blowing ratio, Bmax=2.

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Figure 9

Urms∕Uin plots of the wakes/jets (Case 6) configuration. The nondimensional time is labeled in the upper right corner of each plot.

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Figure 10

Time history plots (Urms∕Uin) depicting wake/jet and wake only interaction with the separation bubble

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Figure 11

Integrated isovelocity surfaces (Cases 6 and 2) at each data acquisition time. The data were normalized by the size of the no control separation bubble.




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