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Research Papers

Hot-Film Measurements on a Low Pressure Turbine Linear Cascade With Bypass Transition

[+] Author and Article Information
Reinaldo A. Gomes

Mem. ASME
Institute of Jet Propulsion,
University of the German
Federal Armed Forces Munich,
Neubiberg 85577, Germany
e-mail: reinaldo.gomes@unibw.de

Stephan Stotz

Institute of Jet Propulsion,
University of the German
Federal Armed Forces Munich,
Neubiberg 85577, Germany
e-mail: stephan.stotz@unibw.de

Franz Blaim

Institute of Jet Propulsion,
University of the German
Federal Armed Forces Munich,
Neubiberg 85577, Germany
e-mail: franz.blaim@unibw.de

Reinhard Niehuis

Professor
Mem. ASME
Institute of Jet Propulsion,
University of the German
Federal Armed Forces Munich,
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 January 21, 2015; final manuscript received January 26, 2015; published online March 24, 2015. Editor: Ronald Bunker.

J. Turbomach 137(9), 091007 (Sep 01, 2015) (11 pages) Paper No: TURBO-15-1016; doi: 10.1115/1.4029967 History: Received January 21, 2015; Revised January 26, 2015; Online March 24, 2015

Transition of the state of the boundary layer from laminar to turbulent plays an important role in the aerodynamic loss generation on turbine airfoils. An accurate simulation of the transition process and of the state of the boundary layer is therefore crucial for prediction of the aerodynamic efficiency of components in rotating machines. A lot of the research in the past years dealt with the transition over laminar separation bubbles, especially concerning flows in low pressure turbines (LPTs) of air jet engines. Nevertheless, bypass transition is also frequent in turbomachines at higher Reynolds numbers as well as for properly designed profiles. Compared with transition over a laminar separation bubble, a bypass transition is experimentally much more difficult to detect with standard measurement techniques. In such cases it becomes necessary to use more sophisticated techniques, such as hot-film anemometry, hot wires, or Preston probes in order to obtain accurate information on the state of the boundary layer. The study presented is carried out using a linear cascade with a LPT blade profile with strong front loading and gentle flow deceleration at the rear suction side of the blade. Measurements were performed at the high-speed cascade wind tunnel of the Institute of Jet Propulsion at engine relevant Mach and Reynolds numbers. Emphasis is put on the evaluation of the different transition processes at midspan and its influence on profile losses. The data postprocessing was adapted for compressible flows, which allows a more accurate determination of the transition area as well as qualitatively better distributions of the wall shear stress. Finally, comparisons with simulations, using computational fluid dynamics (CFD) tools, are performed and fields for improvement of the turbulence and transition models are identified.

Copyright © 2015 by ASME
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Figures

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Fig. 1

The high-speed cascade wind tunnel

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Fig. 2

Typical histograms of the voltage deviation for laminar, transitional, and turbulent boundary layer flow

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Fig. 3

Static pressure distribution on the suction side at different Reynolds numbers

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Fig. 4

Scaled QWSS on the suction side for all Reynolds numbers

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Fig. 5

QWSSc, rms(e), and skew(e) on the suction side for Re2,s=40,000

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Fig. 6

QWSSc, rms(e), and skew(e) on the suction side for Re2,s = 400,000

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Fig. 7

Intermittency in the transition zone for all investigated Reynolds numbers

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Fig. 8

Relative velocity in boundary layer on suction side at trailing edge

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Fig. 9

Energy density spectrum on different positions for Re2,s = 400,000

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Fig. 10

Energy density spectrum on different positions for Re2,s=40,000

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Fig. 11

Comparison of CFD with experiments of the static pressure distribution on the suction side

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Fig. 12

QWSS and numerically evaluated wall shear stress at Re2,s = 400,000

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Fig. 13

rms(e) from experiment and turbulence kinetic energy at the wall from CFD at Re2,s = 400,000

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Fig. 14

QWSS and numerically evaluated shear stress at Re2,s=40,000

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Fig. 15

rms(e) from experiment and turbulence kinetic energy at the wall from CFD at Re2,s=40,000

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Fig. 16

Profile loss normalized by values at Re2,s = 400,000 as function of the Reynolds number

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