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Research Papers

Aerothermal Investigation of a Single Row Divergent Narrow Impingement Channel by Particle Image Velocimetry and Liquid Crystal Thermography

[+] Author and Article Information
Alexandros Terzis

Group of Thermal Turbomachinery (GTT),
École Polytechnique Fédérale
de Lausanne (EPFL),
Lausanne CH-1015, Switzerland
e-mail: alexandros.terzis@me.com

Christoforos Skourides

Interdisciplinary Aerodynamics Group (IAG),
École Polytechnique Fédérale
de Lausanne (EPFL),
Lausanne CH-1015, Switzerland

Peter Ott

Group of Thermal Turbomachinery (GTT),
École Polytechnique Fédérale
de Lausanne (EPFL),
Lausanne CH-1015, Switzerland

Jens von Wolfersdorf, Bernhard Weigand

Institute of Aerospace Thermodynamics (ITLR),
University of Stuttgart,
Pfaffenwaldring 31,
Stuttgart D-70569, Germany

Manuscript received July 12, 2015; final manuscript received December 18, 2015; published online January 20, 2016. Assoc. Editor: David G. Bogard.

J. Turbomach 138(5), 051003 (Jan 20, 2016) (9 pages) Paper No: TURBO-15-1141; doi: 10.1115/1.4032328 History: Received July 12, 2015; Revised December 18, 2015

Integrally cast turbine airfoils with wall-integrated cooling cavities are greatly applicable in modern turbines providing enhanced heat exchange capabilities compared to conventional cooling passages. In such arrangements, narrow impingement channels can be formed where the generated crossflow is an important design parameter for the achievement of the desired cooling efficiency. In this study, a regulation of the generated crossflow for a narrow impingement channel consisting of a single row of five inline jets is obtained by varying the width of the channel in the streamwise direction. A divergent impingement channel is therefore investigated and compared to a uniform channel of the same open area ratio. Flow field and wall heat transfer experiments are carried out at engine representative Reynolds numbers using particle image velocimetry (PIV) and liquid crystal thermography (LCT). The PIV measurements are taken at planes normal to the target wall along the centerline for each individual jet, providing quantitative flow visualization of jet and crossflow interactions. The heat transfer distributions on the target plate of the channels are evaluated with transient techniques and a multilayer of liquid crystals (LCs). Effects of channel divergence are investigated combining both the heat transfer and flow field measurements. The applicability of existing heat transfer correlations for uniform jet arrays to divergent geometries is also discussed.

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Figures

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Fig. 1

Turbine airfoil with near wall integrated microcooling channels. Adopted from Ref. [2].

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Fig. 2

Wall-integrated narrow impingement cooling cavities. Adopted from Ref. [11].

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Fig. 3

The impingement cooling test rig of EPFL-GTT

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Fig. 4

Schematic representation of the test models

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Fig. 5

Schematic of PIV setup

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Fig. 6

(a) Jet massflow distribution and (b) crossflow development at ReD = 36,950

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Fig. 7

Time-averaged velocity fields for the uniform and divergent impingement channel, y = 0, ReD = 36,950

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Fig. 8

Location of the jet upstream vortex as a function of Gcf/Gj for both channels

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Fig. 9

PIV obtained velocity profiles in the streamwise direction for various vertical positions: (a) jet 1, (b) jet 4, and (c) jet 5

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Fig. 10

Surface contour of NuD/(ReD0.7Pr1/3) for the uniform (top) and the divergent (bottom) impingement channel at ReD = 36,950. Flow direction from left to right.

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Fig. 11

Spanwise-averaged NuD for ReD = 36,950

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Fig. 12

Applicability of Florschuetz et al. [13] and Terzis et al. [23] heat transfer correlations for divergent channel geometries. X/D = 6.6, Y¯/D=5.5, and Z/D = 2. Mean value of NuD,j/(ReD,j0.7Pr1/3) over the full range of ReD (14,730–45,270): (a) uniform channel and (b) divergent channel.

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Fig. 13

Step-changed heat transfer area considered prediction of divergent channel area-averaged Nu¯¯D

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Fig. 14

Relative TP for the two channels

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