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Research Papers

Mach Number Distribution and Profile Losses for Low-Pressure Turbine Profiles With High Diffusion Factors

[+] Author and Article Information
Roland Brachmanski

Institute of Jet Propulsion,
Universität der Bundeswehr München,
Neubiberg 85577, Germany
e-mail: roland.brachmanski@unibw.de

Reinhard Niehuis

Institute of Jet Propulsion,
Universität der Bundeswehr München,
Neubiberg 85577, Germany
e-mail: reinhard.niehuis@unibw.de

1Corresponding author.

Contributed by the International Gas Turbine Institute (IGTI) of ASME for publication in the JOURNAL OF TURBOMACHINERY. Manuscript received August 7, 2016; final manuscript received March 5, 2017; published online May 9, 2017. Assoc. Editor: Guillermo Paniagua.

J. Turbomach 139(10), 101002 (May 09, 2017) (10 pages) Paper No: TURBO-16-1187; doi: 10.1115/1.4036436 History: Received August 07, 2016; Revised March 05, 2017

The results of this investigation come from two linear cascades at high diffusion factors (DFs). The measurements presented for each low-pressure turbine (LPT) profile were conducted at midspan under a range of Reynolds- and exit Mach numbers. The exit Mach number was varied in a range covering low subsonic up to values where a transonic flow regime on the suction side of the blade could be expected. This work focuses on two profiles with a diffusion factor in a range of 0.18DF0.22, where values in this range are considered as a comparable for the two cascades. Profile A is a front-loaded design and has shown no obvious flow separation on the suction side of the blade. Compared to the design A, design B is a more aft-loaded profile which exhibits flow separation on the suction side for all Reynolds numbers investigated. The integral total pressure losses were evaluated by wake traverses downstream of the airfoil. To determine the isentropic Mach numbers and the character of the boundary layer along the suction side of the profile, the static pressure measurements and traverses with a flattened Pitot probe were carried out. A correlation between the position of maximum Mach number on the suction side and the integral total pressure losses has been successfully established. The results show that the optimum location of peak Mach number to minimize integral total pressure losses is significantly dependent on the Reynolds number. However, the correlation presented in this paper, which is based on the data of the integral total pressure losses of an attached boundary layer, is not able to predict the integral total pressure loss or the location of the maximum Mach number on the suction side of the blade when an open separation bubble occurs.

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Figures

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Fig. 1

The high-speed cascade wind tunnel

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Fig. 2

Schematic of the cascade co-ordinate system (geometry not to scale)

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Fig. 3

Mach number distribution of profile B

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Fig. 4

Mach number distribution of profile A

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Fig. 5

Wake traverses of profile B

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Fig. 6

Wake traverses of profile A

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Fig. 7

Integral total pressure losses as a function of maximum Mach number location

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Fig. 8

Derivatives of the parabola

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Fig. 9

Integral total pressure losses as a function of maximumMach number location for high DF and variation of Tu intensities

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Fig. 10

Mach number distribution of profile B at Re2th=125,000 and variation of Tu intensities

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Fig. 11

Wake traverses of profile B at Re2th=125,000 for different Tu intensities

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Fig. 12

Dynamic pressure distribution of design B at Re2th=125,000 and with variation of Tu intensities

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Fig. 13

Trailing edge profiles of design B at Re2th=125,000 and with variation of Tu intensities

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Fig. 14

Mach number distributions of the profile B at Re2th=125,000 at high Tu intensities

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Fig. 15

Mach number distributions of the profile B at Re2th=125,000 at low Tu intensities

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Fig. 16

Friction factors of design B at Re2th=125,000 and variation of Tu intensities

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