Research Papers

Endwall Loss and Mixing Analysis of a High Lift Low Pressure Turbine Cascade

[+] Author and Article Information
M. Eric Lyall

Aerospace Systems Directorate,
Air Force Research Laboratory,
1950 Fifth Street,
Wright Patterson AFB, OH 45433
e-mail: michael.lyall@wpafb.af.mil

Paul I. King

Air Force Institute of Technology,
2950 Hobson Way, Bldg. 641,
Wright Patterson AFB, OH 45433
e-mail: paul.king@afit.edu

Rolf Sondergaard

Aerospace Systems Directorate,
Air Force Research Laboratory,
1950 Fifth Street,
Wright Patterson AFB, OH 45433
e-mail: rolf.sondergaard@wpafb.af.mil

Contributed by the International Gas Turbine Institute (IGTI) of ASME for publication in the JOURNAL OF TURBOMACHINERY. Manuscript received April 18, 2012; final manuscript received September 19, 2012; published online June 26, 2013. Editor: David Wisler.

J. Turbomach 135(5), 051006 (Jun 26, 2013) (10 pages) Paper No: TURBO-12-1033; doi: 10.1115/1.4007801 History: Received April 18, 2012; Revised September 19, 2012

A high lift low pressure turbine (LPT) profile designated L2A is used as a test bed for studying the origin of endwall mixing loss and the role of vortical structures in loss development. It is shown analytically and experimentally that the mixing forces within the endwall wake can be decoupled into either mean flow or turbulent forces and can be further classified as either reversible or irreversible. Among the irreversible forces, mean flow shear is negligible compared to turbulent shear, suggesting that turbulence dissipation is the dominant cause of loss generation. As a result, the mean flow components of the vortical structures do not generate significant mixing losses. Rather than mixing effects, the mean flow of the vortices causes the suction surface boundary layer to separate inside the passage, thereby generating the large low energy regions typical of endwall flows. Losses are generated as the low energy regions mix out. This vortex separation effect is demonstrated with an experiment using a profile fence and pressure surface modification near the endwall. The findings in this paper suggest that profile modifications near the endwall that suppress flow separation may provide loss reductions additive to modifications aimed at weakening vortical structures, such as endwall contouring.

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Fig. 1

Schematic of AFRL low speed wind tunnel test section

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Fig. 2

Schematic depicting the cascade and secondary flow (primed) coordinate system definitions

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Fig. 3

Pressure loading of the L2A profile, taken from Lyall et al. [12]

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Fig. 5

Secondary vorticity, total pressure loss coefficients (ΔY = 0.05 for contours), and secondary velocity vectors within the measurement plane (see Fig. 2)

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Fig. 6

Decomposition of the mixing forces at 20% span in the measurement plane (see Fig. 2)

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Fig. 4

Mechanical work and loss coefficients at 20% span in the measurement plane (see Fig. 2)

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Fig. 8

Mean flow and viscous effects for various spanwise positions

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Fig. 9

Sketch demonstrating the effect of a suction surface boundary layer fence on the boundary layer flow

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Fig. 10

Diagram of experimental setup using fences and putty

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Fig. 11

Flood plots of secondary vorticity, Y contours, and secondary velocity vectors with and without fences and putty

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Fig. 7

Flood plots of mixing force variables overlaid with Y contours and secondary velocity vectors




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