Research Papers

High Resolution Heat Transfer Measurement on Flat and Contoured Endwalls in a Linear Cascade

[+] Author and Article Information
Benoit Laveau

e-mail: blaveau@ethz.ch

Reza S. Abhari

Laboratory for Energy Conversion,
ETH Zurich,
Sonnegstrasse 3,
CH-8092 Zurich, Switzerland

Michael E. Crawford

Siemens Energy, Inc.,
4400 Alafaya Trail,
Orlando, FL 32826

Ewald Lutum

MTU Aero Engines,
Dachauer Str. 665,
80995 Munich, Germany

Contributed by the International Gas Turbine Institute (IGTI) of ASME for publication in the JOURNAL OF TURBOMACHINERY. Manuscript received July 26, 2012; final manuscript received September 2, 2012; published online June 5, 2013. Assoc. Editor: David Wisler.The content of this paper is copyrighted by Siemens Energy, Inc. and is licensed to ASME for publication and distribution only. Any inquiries regarding permission to use the content of this paper, in whole or in part, for any purpose must be addressed to Siemens Energy, Inc. directly.

J. Turbomach 135(4), 041020 (Jun 05, 2013) (9 pages) Paper No: TURBO-12-1155; doi: 10.1115/1.4007725 History: Received July 26, 2012; Revised September 02, 2012

In order to continue increasing the efficiency of gas turbines, a significant effort is being made to reduce losses induced by secondary flows in turbine stages. In addition to their impact on aerodynamic losses, these vortical structures are also the source of large heat transfer variations across the passage. A substantial reduction of the secondary flow losses can be achieved with a contoured endwall. However, a change in the vortical pattern can dramatically impact the thermal loads on the endwalls and lead to higher cooling requirements in those areas. This paper focuses on heat transfer measurements made in a passage with either flat or contoured endwalls. The experimental data are supplemented with numerical predictions of the heat transfer data. The measurements are carried out on an isothermal endwall equipped with symmetric airfoils. The paper presents measurements at M = 0.3, corresponding to a Reynolds number ReCax=4.6×105. An infrared camera is used to provide high-resolution surface temperature data on the endwall. The surface is equipped with an insulating layer (Kapton), allowing the calculation of heat flux through the endwall. The heat transfer quantities, namely the heat transfer coefficient and the adiabatic wall temperature, are then derived from a set of measurements at different isothermal plate temperatures. The numerical predictions clarify the link between the change in the heat transfer quantities and the changes in the flow field due to endwall contouring. Finally, numerically predicted heat transfer data are deduced from a set of adiabatic and diabatic simulations that are compared to the experimental data. The comparison focuses on the differences in the regions with endwall contouring, where a significant difference in the heat transfer coefficient between flat and contoured endwalls is measured but underpredicted numerically.

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Fig. 1

Sketch of an airfoil endwall junction including the horseshoe vortex (from Ref. [14])

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Fig. 3

Test section (opened) of the facility. Three NACA profiles mounted on the isothermal plate.

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Fig. 2

Test section configuration for heat transfer measurements

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Fig. 6

(a) Illustration of the linear fit procedure (top) to deduce the heat transfer coefficient and the adiabatic wall temperature. (b) Position of the points for the linear fit illustrated in (a).

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Fig. 5

Shape of the contoured endwall. Variation of surface height (in mm) along the passage.

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Fig. 4

Contoured endwall case. Copper insert covered with the insulating Kapton layer.

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Fig. 7

Absolute uncertainty in measured adiabatic wall temperature in the case with contoured endwall

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Fig. 13

Top—heat transfer coefficient values in the middle of the passage (Y = 0.0225 m) extracted from the measurements of the flat cases A (red–filled symbols) and B (blue–empty symbols); the CFD simulation and a boundary layer calculation performed using TEXSTAN. Bottom—Mach number variation in the middle of the passage extracted from the CFD calculation of the flat case.

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Fig. 14

Delta temperature (Eq. (4)) values in the middle of the passage (Y = 0.0225 m). The data are extracted from the measurements of the flat cases A (red–empty symbols) and B (blue–filled symbols) and results from a boundary layer calculation performed using TEXSTAN.

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Fig. 9

Heat transfer coefficient extracted along the line X = 0.065 for the different meshes

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Fig. 10

Comparison of laterally averaged measured heat transfer in a nondimensional form with correlation (Eq. (8)) and a TEXSTAN calculation

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Fig. 11

Heat transfer coefficient measured at Ma = 0.28 for the flat (bottom—case B) and contoured endwall (top—case C) configurations

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Fig. 12

Delta temperature between total inlet and adiabatic wall temperature measured at Ma = 0.28 for the flat (bottom—case B) and contoured endwall (top—case C) configurations

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Fig. 17

Endwall static pressure nondimensionalized with total inlet pressure and pressure gradient (arrows) from CFD shown for both flat (left) and contoured (right) endwalls

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Fig. 18

Isosurface of constant Q value from the CFD predictions of the flat (left) and contoured (right) cases

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Fig. 19

Axial slices of the horseshoe vortex from CFD calculations for the flat (left) and contoured (right) endwalls. Lines of isoswirling strength are displayed in perpendicular slices at the same axial positions for both cases. The endwall surface is colored with the Z coordinate.

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Fig. 15

Comparison of heat transfer measurements (top) with CFD predictions (bottom) for the flat endwall case at Ma = 0.28 and ReCax = 4.5×105

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Fig. 16

Relative heat transfer augmentation (hcontoured–hflat)/hflat in % plotted for both the experiments (top) and the numerical predictions (bottom) at Ma = 0.28. The lines represent the changes in surface altitude.




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