Research Papers

Improving Intermediate Pressure Turbine Performance by Using a Nonorthogonal Stator

[+] Author and Article Information
Sungho Yoon

e-mail: sungho.yoon@cantab.net

Graham Pullan

Whittle Laboratory,
Cambridge University,
Cambridge, UK

1Currently, GE Global Research Center, Munich, Germany.

Contributed by the International Gas Turbine Institute (IGTI) of ASME for publication in the Journal of Turbomachinery. Manuscript received February 2, 2013; final manuscript received February 9, 2013; published online September 26, 2013. Editor: David Wisler.

J. Turbomach 136(2), 021012 (Sep 26, 2013) (8 pages) Paper No: TURBO-13-1015; doi: 10.1115/1.4023941 History: Received February 02, 2013; Revised February 09, 2013

Intermediate pressure (IP) turbines in high bypass ratio civil aeroengines are characterized by a significant increase in radius and a low aspect ratio stator. Conventional aerodynamic designs for the IP turbine stator have had leading and trailing edges orthogonal to the hub and casing end walls. The IP turbine rotor, however, is stacked radially due to stress limits. These choices inevitably lead to a substantial gap between the IP stator and rotor at the outer diameter in a duct that is generally diffusing the flow due to the increasing radius. In this low Mach number study, the IP stator is redesigned, incorporating compound sweep so that the leading and trailing edges are no longer orthogonal to the end walls. Computational investigations showed that the nonorthogonal stator reduces the flow diffusion between the stator and rotor, which yields two benefits: The stator trailing edge velocity was reduced, as was the boundary layer growth on the casing end wall within the gap. Experimental measurements confirm that the turbine with the nonorthogonal stator has an increased efficiency by 0.49%, while also increasing the work output by 4.6%, at the design point.

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Fig. 5

Meridional plane of the IP turbine with orthogonal (datum) and nonorthogonal (linear swept) stators

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Fig. 6

The effect of linear sweep on the calculated efficiency of the IP turbine

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Fig. 4

Estimated ratio of profile loss for a swept blade to an orthogonal blade at the same loading (Pullan and Harvey, [7])

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Fig. 3

The effect of sweep on streamlines and blade loading (Potts [4] and Denton and Xu [5])

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Fig. 2

Illustration of how an orthogonal stator and radially stacked rotor in a high flare annulus leads to large diffusion in the region towards the casing (marked “A”)

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Fig. 1

A three-shaft civil aeroengine (Cumpsty [6])

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Fig. 7

The calculated pitchwise area-averaged pressure contours of the IP turbine with the orthogonal and nonorthogonal linear swept stator

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Fig. 8

The calculated pitchwise mass-averaged Mach number near the casing for the orthogonal and nonorthogonal linear swept stator

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Fig. 9

Calculated contours of pitchwise averaged normalized lost efficiency of the IP turbine with the orthogonal, linear sweep and compound sweep stators

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Fig. 10

Meridional view showing datum orthogonal stator and optimized nonorthogonal (compound sweep)

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Fig. 14

Measured efficiency curve of the IP turbine with the orthogonal and nonorthogonal stators

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Fig. 11

Calculated pitchwise averaged normalized lost efficiency at the stage exit for the different stator blades

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Fig. 12

The IP turbine rig with an orthogonal stator at the Whittle Laboratory

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Fig. 13

Traverse planes in the IP turbine stage

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Fig. 16

Contours of measured stagnation pressure coefficient at the stator exit traverse plane

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Fig. 15

Calculated and measured absolute meridional yaw angle distributions at the stator exit

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Fig. 17

Calculated contours of pressure for a high-speed IP turbine on the blade to blade surface at midspan



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