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Research Papers

The Application of Flow Control to an Aft-Loaded Low Pressure Turbine Cascade With Unsteady Wakes

[+] Author and Article Information
Jeffrey P. Bons, Jon Pluim, Kyle Gompertz, Matthew Bloxham

Department of Aerospace Engineering, Ohio State University, Columbus, OH 43210

John P. Clark

Propulsion Directorate, Air Force Research Laboratory, Wright-Patterson AFB, OH 45433

J. Turbomach 134(3), 031009 (Jul 14, 2011) (11 pages) doi:10.1115/1.4000488 History: Received August 22, 2008; Revised June 26, 2009; Published July 14, 2011; Online July 14, 2011

The synchronous application of flow control in the presence of unsteady wakes was studied on a highly loaded low pressure turbine blade. At low Reynolds numbers, the blade exhibits a nonreattaching separation bubble under steady flow conditions without upstream wakes. Unsteady wakes from an upstream vane row are simulated with a moving row of bars. The separation zone is modified substantially by the presence of unsteady wakes, producing a smaller separation zone and reducing the area-averaged wake total pressure loss by more than 50%. The wake disturbance accelerates transition in the separated shear layer but stops short of reattaching the flow. Rather, a new time-averaged equilibrium location is established for the separated shear layer. The focus of this study was the application of pulsed flow control using two spanwise rows of discrete vortex generator jets. The jets were located at 59% Cx, approximately the peak cp location, and at 72% Cx. The most effective separation control was achieved at the upstream location. The wake total pressure loss decreased 60% from the wake-only level and the cp distribution fully recovered its high Reynolds number shape. The jet disturbance dominates the dynamics of the separated shear layer, with the wake disturbance assuming a secondary role only. When the pulsed jet actuation was initiated at the downstream location, synchronizing the jet to actuate between wake events was key to producing the most effective separation control. Evidence suggests that flow control using vortex generator jets (VGJs) will be effective in the highly unsteady low pressure turbine environment of an operating gas turbine, provided the VGJ location and amplitude are adapted for the specific blade profile.

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Copyright © 2012 by American Society of Mechanical Engineers
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Figures

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Figure 1

Prediction of cp for L1A, Pack B, and L1M profiles. Inset shows aft portion of blade profiles.

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Figure 2

Schematic of L1A linear cascade

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Figure 3

Measured and predicted cp values for L1A profile at three Reynolds numbers

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Figure 4

Prediction of area-averaged wake total pressure loss (γint) for L1A compared with experimental cascade measurements

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Figure 5

Time-averaged contour plots of umean/Uin (top), urms/Uin (%) (middle), and skewness (bottom) presented in wall normal axial chord coordinates for (a) L1M, (b) Pack B, and (c) L1A. All with no wakes and no VGJs at Rec=20,000.

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Figure 6

Suction surface acceleration parameter plotted against x/Cx calculated from cp predictions for the L1A, Pack B, and L1M profiles shown in Fig. 1 and for the L1A experimental data in Fig. 3(Re=60,000)

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Figure 7

cp data for baseline, wakes, and wakes+upstream VGJ cases at Re=20,000 compared with prediction for L1A

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Figure 8

Contour plots of umean/Uin and urms/Uin at 12 discrete phases of wake passing period (t/T indicated in upper right corner). Data for wake only (no VGJs). Re=20,000. Scale identical to Fig. 5.

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Figure 9

Contour plots of umean/Uin and urms/Uin at 12 discrete phases of wake passing period (t/T indicated in upper right corner). Data for wakes with upstream VGJs at 59% Cx with B=1.6. Re=20,000. VGJs are active for 0.05<t/T<0.4, corresponding to Fig. 1. Scale identical to Fig. 5.

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Figure 10

Pulsed VGJ blowing ratio plotted against dimensionless time. x/Cx=59%.

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Figure 11

Time-space plots of urms/Uin at y/Cx=0.013 and 0.038 for wake only and wakes+VGJs. The highlighted band from 0.057<x/Cx<0.59 indicates approximate separated shear layer location for baseline case (no wakes, no VGJs) taken from Fig. 5.

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Figure 12

Wake total pressure loss normalized by loss with wake only. Data for VGJ actuation at 59% Cx and 72% Cx with B=1.6, plotted against dimensionless time. Re=20,000.

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Figure 13

Contour plots of time-averaged umean/Uin. Data for baseline, wake only, upstream VGJ only, and wakes with upstream VGJs. Re=20,000.

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