Research Papers

The Effects of Trailing Edge Thickness on the Losses of Ultrahigh Lift Low Pressure Turbine Blades

[+] Author and Article Information
Chao Zhou

State Key Laboratory for Turbulence
and Complex Systems,
College of Engineering,
Peking University,
Beijing 100871, China
e-mail: czhou@pku.edu.cn

Howard Hodson, Christoph Himmel

Whittle Laboratory,
Department of Engineering,
University of Cambridge,
Cambridge CB3 0DY, UK

1Corresponding author.

Contributed by the International Gas Turbine Institute (IGTI) of ASME for publication in the JOURNAL OF TURBOMACHINERY. Manuscript received July 6, 2013; final manuscript received December 14, 2013; published online February 12, 2014. Editor: Ronald Bunker.

J. Turbomach 136(8), 081011 (Feb 12, 2014) (9 pages) Paper No: TURBO-13-1136; doi: 10.1115/1.4026456 History: Received July 06, 2013; Revised December 14, 2013

Experimental, numerical and analytical methods were used to investigate the effects of the blade trailing edge thickness on the profile loss of ultrahigh-lift low-pressure turbine blades. Two cascades, the T106C and the T2, were studied. The loss obtained based on the data at the blade trailing edge plane and the plane 0.3 Chord downstream of the trailing edge agree with each other for T106C blade with and without upstream wakes at different Reynolds numbers. The blade profile losses were broken down as the suction surface boundary loss, the pressure side boundary loss and the mixing loss downstream of the trailing edge for six Reynolds numbers. Trailing edge thicknesses varying from 1.4% to 4.7% pitch were investigated at a Reynolds number of 210,000. It was found that the flow distributions across the passage at the trailing edge planes were highly nonuniform. In particular, and as a result, the trailing edge base pressure was higher than the mixed-out static pressure, so the contribution of the base pressure to the mixing loss downstream of the trailing edge plane was to reduce the loss. When the trailing edge thickness increases, there are three main effects: (1) the area with high base pressure region increases, which tends to reduce the downstream mixing loss; (2) the base pressure reduces, which tends to increase the loss; and (3) the flow diffusion downstream of the trailing edge, which tends to increase the loss. The overall result is the combined effect. For the T106C cascade, increasing the trailing edge thickness from 1.9% pitch to 2.8% pitch has a small effect on the loss. Further increasing the trailing edge thickness increases the loss. The T2 blade has a higher lift than the T106C blade, so the effects of the base pressure in reducing the mixing loss downstream of the trailing edge is more evident. The experimental results show that the profile loss first decreases and then increases as the trailing edge thickness increases. CFD, using the transition k-ω SST model and the k-ω SST model, provides good predictions of the aerodynamic performance. It was used to study the cases with trailing edge thicknesses of 1.4% pitch and 2.9% pitch. The profile loss is almost the same for these two trailing edge thickness. The results show that it is possible to use thicker blade trailing edges in low pressure turbines without aerodynamic penalty. This can lead to benefits in terms of mechanical integrity and manufacturing cost reductions.

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Fig. 1

Layout of cascade (Zhang [9])

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Fig. 2

Schematic of the T106C blade passage and measurement planes

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Fig. 3

Schematic of the Naptune probe

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Fig. 4

Changing the thickness of blade trailing edge

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Fig. 5

Midspan Cp distribution of T106C blade, Re = 210,000, exp.

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Fig. 6

Trailing edge plane normalized static pressure distribution of T106C, TE = 1.9% s

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Fig. 7

Comparison of the mixed-out loss (Yp) calculated from measurements in the trailing edge plane and in a plane 0.3 C downstream of the trailing edge

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Fig. 8

Base pressure coefficient (Cpb) development based on mixed-out reference values

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Fig. 9

Loss break down of T106C, Re = 50,000, exp.

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Fig. 10

Effects of TE thickness on Cpb, T106C, Re = 210,000, exp.

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Fig. 11

Effects of TE thickness on mixed-out profile loss, T106C, Re = 210,000

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Fig. 12

Cp distribution, T2, TE = 1.4%s, Re = 210,000

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Fig. 13

Cp distribution, T2, CFD, Re = 210,000

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Fig. 14

Pressure distribution at trailing edge plane of T2 blade (normalized as Cpb), Re = 210,000

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Fig. 15

Effects of trailing edge thickness on the mixed-out profile loss, T2 blade, Re = 210,000

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Fig. 16

Effect of trailing edge thickness on base pressure coefficient of T2 blade, exp., Re = 210,000

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Fig. 17

Sensitivity of mixing loss prediction to variations in Cpb for T2 blade, mixing calculation based on measured data at trailing edge plane, Re = 210,000

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Fig. 18

Effects of trailing edge thickness on exit angle of the T2 blade, exp., Re = 210,000




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