Research Papers

Aerodynamics of a Low-Pressure Turbine Airfoil at Low Reynolds Numbers—Part I: Steady Flow Measurements

[+] Author and Article Information
Brian R. McAuliffe

Institute for Aerospace Research,
National Research Council of Canada,
Ottawa, ON, K1A 0R6, Canada

Steen A. Sjolander

Department of Mechanical and Aerospace Engineering,
Carleton University,
Ottawa, ON, K1S 5B6, Canada

Aerodynamics Group United Technologies, Pratt & Whitney
East Hartford, CT, 06118

1Corresponding author. e-mail: ali.mahallati@nrc-cnrc.gc.ca.

Contributed by the International Gas Turbine Institute (IGTI) of ASME for publication in the JOURNAL OF TURBOMACHINERY. Manuscript received July 8, 2011; final manuscript received August 4, 2011 published online November 6, 2012. Editor: David Wisler.

J. Turbomach 135(1), 011010 (Nov 06, 2012) (9 pages) Paper No: TURBO-11-1102; doi: 10.1115/1.4006319 History: Received July 08, 2011; Revised August 04, 2011

This two-part paper presents a detailed experimental investigation of the laminar separation and transition phenomena on the suction surface of a high-lift low-pressure turbine airfoil, PakB. The first part describes the influence of Reynolds number, freestream turbulence intensity and turbulence length scale on the PakB airfoil under steady inflow conditions. The present measurements are distinctive in that a closely-spaced array of hot-film sensors has allowed a very detailed examination of the suction surface boundary layer behavior. In addition, this paper presents a technique for interpreting the transition process in steady, and periodically unsteady, separated flows based on dynamic and statistical properties of the hot-film measurements. Measurements were made in a low-speed linear cascade facility at Reynolds numbers between 25,000 and 150,000 at three freestream turbulence intensity levels of 0.4%, 2%, and 4%. Two separate grids were used to generate turbulence intensity of 4% with integral length scales of about 10% and 40% of the airfoil axial chord length. While the higher levels of turbulence intensity promoted earlier transition and a shorter separation bubble, turbulence length scale did not have a noticeable effect on the transition process. The size of the suction side separation bubble increased with decreasing Reynolds number, and under low freestream turbulence levels the bubble failed to reattach at low Reynolds numbers. As expected, the losses increased with the length of the separation bubble, and increased significantly when the bubble failed to reattach.

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Fig. 1

Variable incidence linear cascade test section

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Fig. 2

Static pressure coefficient distributions

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Fig. 3

Time histories of hot-film signals at Rei = 100,000 at FSTI = 0.4% (height of separation bubble exaggerated)

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Fig. 4

Suction surface loading and hot-film data at Rei = 50,000 and Rei = 100,000 - FSTI

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Fig. 5

Normalized mixed-out pressure losses

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Fig. 6

Suction surface loading and hot-film data at Rei = 50,000 and Rei = 100,000 - integral length scale




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