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Research Papers

Film Cooling on Highly Loaded Blades With Main Flow Separation—Part II: Overall Film Cooling Effectiveness

[+] Author and Article Information
Reinaldo A. Gomes

Research Assistant
e-mail: reinaldo.gomes@unibw.de

Reinhard Niehuis

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

1Corresponding author.

Contributed by the International Gas Turbine Institute (IGTI) of ASME for publication in the JOURNAL OF TURBOMACHINERY. Manuscript received August 18, 2011; final manuscript received August 25, 2011; published online October 31, 2012. Editor: David Wisler.

J. Turbomach 135(1), 011044 (Oct 31, 2012) (9 pages) Paper No: TURBO-11-1188; doi: 10.1115/1.4006569 History: Received August 18, 2011; Revised August 25, 2011

Film cooling experiments were run at the high speed cascade wind tunnel of the University of the Federal Armed Forces Munich. The investigations were carried out with a linear cascade of highly loaded turbine blades. The main targets of the tests were to assess the film cooling effectiveness and the heat transfer in zones with main flow separation. Therefore the blades were designed to force the flow to detach on the pressure side shortly downstream of the leading edge and it reattaches at about half of the axial chord. In this zone, film cooling rows are placed among others for reduction of the size of the separation bubble. The analyzed region on the blade is critical due to the high heat transfer present at the leading edge and at the reattachment line after main flow separation. Film cooling can contribute to a reduction of the size of the separation bubble reducing aerodynamic losses but increases in general heat transfer due to turbulent mixing. The reduction of the size of the separation bubble might also be two-fold since it acts like a thermal insulator on the blade and reducing the size of the bubble might lead to stronger heating of the blade. Film cooling should therefore take into account both: firstly, a proper protection of the surface, and secondly, reduce aerodynamic losses diminishing the extension of the main flow separation. The overall effectiveness of film cooling for a real engine has to combine heat transfer with film cooling effect. In this paper, the overall effectiveness of film cooling, combining results from measurements of the adiabatic film cooling effectiveness and the local heat transfer coefficient are shown. The tests comprise the analysis of the effect of different outlet Mach and Reynolds numbers at engine relevant values and film cooling ratio. A new parameter is introduced which allows for the evaluation of the effect of film cooling accounting at the same time for the change of local heat transfer coefficient. To the authors’ opinion this parameter allows a better, physically based assessment than the strategy using the so-called heat flux ratio. A parameter study is carried out in order to benchmark the effect of changes of the blade design.

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References

Figures

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Fig. 3

Definition of the geometric data on the T120C cascade (not to scale)

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Fig. 4

T120C blade and detail of film cooling (not to scale)

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Fig. 2

Schematic of the test section and cascade instrumentation (not to scale)

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Fig. 1

The high-speed cascade wind tunnel

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Fig. 5

One-dimensional heat flux in the blade

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Fig. 7

Isentropic Mach number on the blade

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Fig. 8

Adiabatic film cooling effectiveness for Ma2,s = 0.87, Re2,s = 390,000

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Fig. 9

TDR for Ma2,s = 0.87, Re2,s = 390,000, ptc/pt1 = 1.03, r = 1 and ξ = 1; variation of K1

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Fig. 10

TDR for Ma2,s = 0.87, Re2,s = 390,000, ptc/pt1 = 1.03, r = 1 and K1 = 8000 W/(m2 K); variation of ξ

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Fig. 6

Blade with finite extension in spanwise direction

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Fig. 12

TDR for Ma2,s = 0.95, Re2,s = 390,000, ptc/pt1 = 1.09, r = 1 and K1 = 8000 W/(m2 K) compared to heat flux ratio

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Fig. 13

ϕ for Ma2,s = 0.95, Re2,s = 390,000, ptc/pt1 = 1.09, r = 1 and K1 = 8000 W/(m2 K)

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Fig. 14

TDR for Ma2,s = 0.87, Re2,s = 390,000

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Fig. 15

TDR for ptc/pt1 = 1.09

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Fig. 11

TDR for Ma2,s = 0.87, Re2,s = 390,000, ptc/pt1 = 1.03, r = 1 and K1 = 8000 W/(m2 K) compared to heat flux ratio

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