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Research Papers

A Comparison of Three Low Pressure Turbine Designs

[+] Author and Article Information
Christian T. Wakelam

Institut fuer Strahlantriebe,
Universitaet der Bundeswehr,
Munich, Germany

Martin Hoeger

MTU Aero Engines,
Munich, Germany

Reinhard Niehuis

Institut fuer Strahlantriebe,
Universitaet der Bundeswehr, Munich, Germany

Contributed by the International Gas Turbine Institute (IGTI) of ASME for publication in the JOURNAL OF TURBOMACHINERY. Manuscript received October 14, 2012; final manuscript received October 20, 2012; published online June 28, 2013. Editor: David Wisler.

J. Turbomach 135(5), 051026 (Jun 28, 2013) (10 pages) Paper No: TURBO-12-1207; doi: 10.1115/1.4023017 History: Received October 14, 2012; Revised October 20, 2012

As part of the current research, three low pressure turbine (LPT) geometries—which were designed with a common pitch, axial chord, inlet angle, and exit Mach number and to create the same nominal level of turning—are compared. Each of the LPT cascades was investigated under a range of Reynolds numbers, exit Mach numbers, and under the influence of a moving bar wake generator. Profile static pressure distributions, wake traverses at 5% and 40% axial chord downstream of the trailing edge, and suction side boundary layer traverses were used to compare the performance of the three designs. The total pressure losses are strongly dependent on both the maximum velocity location as well as the diffusion on the suction surface. The importance of the behavior of the pressure surface boundary layer turned out to be negligible in comparison. Cases with equivalent operating Reynolds number and suction side diffusion level are compared in terms of the total pressure losses that are generated. It is shown that a relationship between loss and suction side maximum velocity location exists. An optimum suction side maximum velocity location depends on the Reynolds number, diffusion factor, and wake passing frequency.

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Figures

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Fig. 1

Schematic of the High Speed Cascade Wind Tunnel

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Fig. 2

Mach distribution from inviscid calculations

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Fig. 3

Integral total pressure loss variation with Reynolds number (steady inlet conditions)

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Fig. 4

Measured Mach number distribution for Re2th (a) 60,000, (b) 150,000, and (c) 400,000

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Fig. 5

(a) Trailing edge profiles and (b) near field wake measurements for Re2th 60,000

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Fig. 6

Near field wake measurements for Re2th 150,000

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Fig. 7

Near field wake measurements for Re2th 400,000

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Fig. 8

Measured Mach number distribution for design B at Re2th 60,000 and a range of exit Mach number

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Fig. 9

Total pressure loss as a function of suction side maximum velocity location

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Fig. 10

Trailing edge boundary layer profiles with and without moving bar wake generator for (a) design A and (b) design B at Re2th 60,000

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Fig. 11

Integral total pressure loss variation with Reynolds number (unsteady inlet conditions)

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Fig. 12

Effect of unsteady inflow on the optimal maximum velocity location at Re2th 60,000

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Fig. 13

Effect of wake passing frequency on the optimal maximum velocity location

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