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Research Papers

Winglets for Improved Aerothermal Performance of High Pressure Turbines

[+] Author and Article Information
John D. Coull

Whittle Laboratory,
University of Cambridge,
1 J. J. Thomson Avenue,
Cambridge CB3 0DY, UK
e-mail: jdc38@cam.ac.uk

Nick R. Atkins

Whittle Laboratory,
University of Cambridge,
1 J. J. Thomson Avenue,
Cambridge CB3 0DY, UK
e-mail: nra27@cam.ac.uk

Howard P. Hodson

Whittle Laboratory,
University of Cambridge,
1 J. J. Thomson Avenue,
Cambridge CB3 0DY, UK
e-mail: hph1000@cam.ac.uk

In addition, the pressure surface edge tends to become rounded, but this has not been considered in the current analysis.

Contributed by the International Gas Turbine Institute (IGTI) of ASME for publication in the JOURNAL OF TURBOMACHINERY. Manuscript received October 10, 2013; final manuscript received February 10, 2014; published online May 2, 2014. Editor: Ronald Bunker.

J. Turbomach 136(9), 091007 (May 02, 2014) (11 pages) Paper No: TURBO-13-1229; doi: 10.1115/1.4026909 History: Received October 10, 2013; Revised February 10, 2014

This paper investigates the design of winglet tips for unshrouded high pressure turbine rotors considering aerodynamic and thermal performance simultaneously. A novel parameterization method has been developed to alter the tip geometry of a rotor blade. A design survey of uncooled, flat-tipped winglets is performed using Reynolds-averaged Navier–Stokes (RANS) calculations for a single rotor at engine representative operating conditions. Compared to a plain tip, large efficiency gains can be realized by employing an overhang around the full perimeter of the blade, but the overall heat load rises significantly. By employing an overhang on only the early suction surface, significant efficiency improvements can be obtained without increasing the overall heat transfer to the blade. The flow physics are explored in detail to explain the results. For a plain tip, the leakage and passage vortices interact to create a three-dimensional impingement onto the blade suction surface, causing high heat transfer. The addition of an overhang on the early suction surface displaces the tip leakage vortex away from the blade, weakening the impingement effect and reducing the heat transfer on the blade. The winglets reduce the aerodynamic losses by unloading the tip section, reducing the leakage flow rate, turning the leakage flow in a more streamwise direction, and reducing the interaction between the leakage fluid and end wall flows. Generally, these effects are most effective close to the leading edge of the tip where the leakage flow is subsonic.

Copyright © 2014 by ASME
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References

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Harvey, N. W., 2004, “Aerothermal Implications of Shroudless and Shrouded Blades,” Turbine Blade Tip Design and Tip Clearance Treatment (VKI Lecture Series 2004-02), von Karman Institute, Sint-Genesius-Rode, Belgium.
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Zhang, Q., O'Dowd, D. O., He, L., Oldfield, M. L. G., and Ligrani, P. M., 2011, “Transonic Turbine Blade Tip Aerothermal Performance With Different Tip Gaps—Part I: Tip Heat Transfer,” ASME J. Turbomach.133(4), p. 041027. [CrossRef]
O'Dowd, D. O., Zhang, Q., Usandizaga, I., He, L., and Ligrani, P. M., 2010, “Transonic Turbine Blade Tip Aero-Thermal Performance With Different Tip Gaps—Part II: Tip Aerodynamic Loss,” ASME Paper No. GT2010-22780. [CrossRef]
Booth, T. C., Dodge, P. R., and Hepworth, H. K., 1981, “Rotor-Tip Leakage Part 1—Basic Methodology,” ASME Paper No. 81-GT-71.
Schabowski, Z., Hodson, H. P., Giacche, D., Power, B., and Stokes, M. R., 2010, “Aeromechanical Optimisation of a Winglet-Squealer Tip for an Axial Turbine,” ASME Paper No. GT2010-23542. [CrossRef]
Zhou, C., Hodson, H. P., and Tibbott, I., 2011, “The Aero-Thermal Performance of a Cooled Winglet Tip in a High Pressure Turbine Cascade,” ASME Paper No. GT2011-46369. [CrossRef]
O'Dowd, D. O., Zhang, Q., He, L., Oldfield, M. L. G., and Ligrani, P. M., 2011, “Aerothermal Performance of a Winglet at Engine Representative Mach and Reynolds Numbers” ASME J. Turbomach., 133(4), p. 041026. [CrossRef]
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Figures

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Fig. 3

NURB representation of a sample geometry, showing the three-dimensional blending

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Fig. 4

Domain and mesh, datum plain tip, 1% tip gap

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Fig. 2

Parameterization of the winglet tip shape

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Fig. 1

Left: control volume for a section of the tip gap; right: cross section normal to the local pressure surface

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Fig. 5

Dependency of heat load and efficiency on mesh density for a tip gap of 1% of span

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Fig. 6

High-speed cascade heat transfer at three tip gaps: top, experiments [10]; bottom, computations

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Fig. 7

Efficiency and heat load ΔH* for a tip gap of 1% of span

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Fig. 8

Variation of efficiency with tip gap size

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Fig. 12

Surface heat flux contours for the plain tip (top), low-H winglet (middle), and high-η winglet (bottom)

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Fig. 14

Surface static pressure presented as isentropic Mach number for the plain tip (top), low-H winglet (middle), and high-η winglet (bottom). The dashed lines indicate Mach number = 1.

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Fig. 13

Distributions of isentropic Mach numbers at varying spanwise height, tip gap of 1% of span

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Fig. 20

Default and fully resolved inlet boundary conditions: total pressure (left), total temperature (center), and whirl angle (right, 5 deg increments)

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Fig. 9

Variation of heat load with tip gap size

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Fig. 10

Tip heat load versus tip area for 1% tip gap

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Fig. 11

Blade heat load versus blade area for 1% tip gap, excluding the tip surface

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Fig. 15

Radially averaged leakage mass flow vectors; from left: plain tip, low-H winglet, high-η winglet. The dashed lines indicate 5% leakage mass fractions.

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Fig. 16

Discharge coefficients versus tangential coordinate; from left: plain tip, low-H winglet, high-η winglet. Dashed lines indicate 5% leakage mass fractions.

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Fig. 17

Slices of total pressure losses in the relative frame, with surface heat flux contours: plain tip (top), low-H winglet (center), and high-η winglet (bottom)

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Fig. 18

Circumferentially averaged whirl angle at domain exit, 10 deg increments

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Fig. 19

Circumferentially averaged absolute total pressure at domain exit

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