Research Papers

Film Cooling on Highly Loaded Blades With Main Flow Separation—Part I: Heat Transfer

[+] Author and Article Information
Reinaldo A. Gomes

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

Reinhard Niehuis

e-mail: reinhard.niehuis@unibw.de
Institute of Jet Propulsion,
University of the German Federal
Armed Forces Munich,
85577 Neubiberg, 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), 011043 (Oct 31, 2012) (9 pages) Paper No: TURBO-11-1187; doi: 10.1115/1.4006568 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 objectives 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 reattach at about half of the axial chord. In this zone, film cooling rows are placed among others for a 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 the main flow separation. Film cooling can contribute to a reduction of the size of the separation bubble reducing aerodynamic losses, however, in general, it increases heat transfer due to turbulent mixing. The reduction of the size of the separation bubble might also be twofold, since it acts like a thermal insulator on the blade and reducing the size of the bubble might lead to a stronger heating of the blade. Film cooling should, therefore, take both into account: first, a proper protection of the surface and second, reducing aerodynamic losses, diminishing the extension of the main flow separation. While experimental results of the adiabatic film cooling effectiveness were shown in previous publications, the local heat transfer is analyzed in this paper. Emphasis is also placed upon analyzing, in detail, the flow separation process. Furthermore, the tests comprise the analysis of the effect of different outlet Mach and Reynolds numbers and film cooling. In part two of this paper, the overall film cooling effectiveness is addressed. Local heat transfer is still difficult to predict with modern numerical tools and this is especially true for complex flows with flow separation. Some numerical results with the Reynolds averaged Navier-Stokes (RANS) and large eddy simulation (LES) show the capability of a commercial solver in predicting the heat transfer.

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Fig. 1

The high-speed cascade wind tunnel

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Fig. 2

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

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Fig. 3

Definition of the geometric data on the T120C cascade and 3D-view on the PS (not to scale)

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Fig. 4

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

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Fig. 5

Back side view of the heating foil

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Fig. 6

Sideview on the mesh for the LES

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Fig. 7

Detail view on the mesh for the LES

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Fig. 8

Isentropic Mach number on the blade

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Fig. 9

Scaled Nusselt number for nominal flow conditions without film cooling; measured and from simulation

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Fig. 10

Streamlines in the separation zone predicted by the RANS simulation and traverse lines for boundary layer measurements

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Fig. 11

Contours of the spanwise component of the vorticity and velocity vectors for timesteps of 0, 0.36, 0.66, and 1.07 ms

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Fig. 12

Velocity profiles of the boundary layer compared to the RANS and LES

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Fig. 13

Turbulent kinetic energy profiles of the boundary layer compared to the RANS and LES

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Fig. 14

Energy density spectrum in the boundary layer at xax/cax = 0.1

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Fig. 15

Scaled Nusselt number for the three operating points without film cooling

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Fig. 16

Scaled Nusselt number for the design operating points with film cooling



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