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Research Papers

# Separated Flow Transition on an LP Turbine Blade With Pulsed Flow Control

[+] Author and Article Information
Jeffrey P. Bons, Daniel Reimann, Matthew Bloxham

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

J. Turbomach 130(2), 021014 (Mar 21, 2008) (8 pages) doi:10.1115/1.2751149 History: Received September 01, 2006; Revised November 14, 2006; Published March 21, 2008

## Abstract

Flow measurements were made on a highly loaded low pressure turbine blade in a low-speed linear cascade facility. The blade has a design Zweifel coefficient of 1.34 with a peak pressure coefficient near 47% axial chord (midloaded). Flow and surface pressure data were taken for $Rec=20,000$ with 3% inlet freestream turbulence. For these operating conditions, a large separation bubble forms over the downstream portion of the blade suction surface, extending from 59% to 86% axial chord. Single-element hot-film measurements were acquired to clearly identify the role of boundary layer transition in this separated region. Higher-order turbulence statistics were used to identify transition and separation zones. Similar measurements were also made in the presence of unsteady forcing using pulsed vortex generator jets just upstream of the separation bubble (50% $cx$). Measurements provide a comprehensive picture of the interaction of boundary layer transition and separation in this unsteady environment. Similarities between pulsed flow control and unsteady wake motion are highlighted.

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## Figures

Figure 1

Linear cascade facility (not actual L1M profiles)

Figure 2

VGJ exit velocity profile (inset of jet configuration)

Figure 3

Data processing flowchart for phase-locked unsteady velocity data

Figure 4

Experimental L1M cp distribution for Rec=20,000 compared to MISES prediction (experimental data for B=0 and 5Hz pulsed)

Figure 5

No control (B=0) at Rec=20,000. Horizontal axis is axial direction from leading edge normalized by cx. Vertical axis is pitchwise direction normalized by cx. Close-up of region 0.64<x∕cx<0.78.

Figure 6

ũ∕Uin contour plots at ten different phases in unsteady VGJ cycle (phase number is in top right corner)

Figure 7

Ensemble-averaged urms∕Uin contour plots at ten different phases in unsteady VGJ cycle

Figure 8

Ensemble-averaged contour plots of various turbulence parameters at ten different phases in unsteady VGJ cycle

Figure 9

Time history plots of turbulence and intermittency at y=6mm(y∕cx=0.027)

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