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TECHNICAL PAPERS

Local Heat/Mass Transfer Characteristics on a Rotating Blade With Flat Tip in Low-Speed Annular Cascade—Part I: Near-Tip Surface

[+] Author and Article Information
Dong-Ho Rhee

Department of Mechanical Engineering, Yonsei University, Seoul 120-749, Korea

Hyung Hee Cho

Department of Mechanical Engineering, Yonsei University, Seoul 120-749, Koreahhcho@yonsei.ac.kr

J. Turbomach 128(1), 96-109 (Feb 01, 2005) (14 pages) doi:10.1115/1.2098756 History: Received October 01, 2004; Revised February 01, 2005

The present study focuses on local heat/mass transfer characteristics on the near-tip region of a rotating blade. To investigate the local heat/mass transfer on the near-tip surface of the rotating turbine blade, detailed measurements of time-averaged mass transfer coefficients on the blade surfaces were conducted using a naphthalene sublimation technique. A low speed wind tunnel with a single stage annular turbine cascade was used. The turbine stage is composed of sixteen guide plates and blades with spacing of 34 mm, and the chord length of the blade is 150 mm. The mean tip clearance is about 2.5% of the blade chord. The tested Reynolds number based on inlet flow velocity and blade chord is 1.5×105 and the rotational speed of blade is 255.8 rpm for the design condition. The result at the design condition was compared with the results for the stationary blade to clarify the rotational effect, and the effects of incoming flow incidence angle were examined for incidence angles ranging from 15 to +7deg. The off-design test condition is obtained by changing the rotational speed maintaining a fixed incoming flow velocity. Complex heat transfer characteristics are observed on the blade surface due to the complicated flow patterns, such as flow acceleration, laminarization, transition, separation bubble and tip leakage flow. The blade rotation causes an increase of the incoming flow turbulence intensity and a reduction of the tip gap flow. At off-design conditions, the heat transfer on the turbine rotor changes significantly due to the flow acceleration/deceleration and the incoming flow angle variation.

Copyright © 2006 by American Society of Mechanical Engineers
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Figures

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Figure 1

Experimental apparatus and test section. (a) Experimental apparatus; (b) test section and rotating disk with blades.

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Figure 2

Guide plate and blade. (a) Geometry; (b) velocity diagram.

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Figure 3

Schematic view of tip clearance

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Figure 4

Actual incidence angle and ReC for various incidence angles. (a) Actual incidence angle; (b) actual ReC.

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Figure 5

Circumferential distributions of velocity magnitude at the plane 10 mm downstream of guide exit for rotating blades

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Figure 6

Static pressure coefficients along the blade at the mid-span at ReC=1.5×105(N=255.8rpm)

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Figure 7

Local heat/mass transfer characteristics on the blade surface at ReC=1.5×105. (a) Mass transfer distribution; (b) classification of flow regimes on the surface.

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Figure 8

Comparison of NuC∕ReC,ex0.5 at the mid-span with other studies for stationary blade. (a) Mass transfer experiments; (b) heat transfer experiments.

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Figure 9

Local ShC distributions on the blade surface at ReC=1.5×105 and N=255.8rpm and its comparison with the stationary case. (a) Contour plot; (b) local distributions.

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Figure 10

Contour plots of ShC on the surface of blade with positive incidence angles at ReC,ex=1.8×105. (a) i=+2.9deg(N=218.8rpm); (b) i=+5deg(N=188.0rpm); (c) i=+7deg(N=154.5rpm).

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Figure 11

Local distributions of ShC at mid-span for the blade with positive incidence angles at ReC,ex=1.8×105

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Figure 12

Local distributions of ShC on the suction side surface at z∕Cx=0.4 for the blade with positive incidence angles at ReC,ex=1.8×105

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Figure 13

Contour plots of ShC on the surface of blade with negative incidence angles at ReC,ex=1.8×105. (a) i=−5deg(N=307.8rpm); (b) i=−10deg(N=349.5rpm); (c) i=−15deg(N=384.2rpm).

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Figure 14

Local distributions of ShC at mid-span for the blade with negative incidence angles at ReC,ex=1.8×105

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Figure 15

Local distributions of ShC on the suction side surface at z∕Cx=0.4 for the blade with negative incidence angles at ReC,ex=1.8×105

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Figure 16

ShC at stagnation point for various incidence angles at ReC,ex=1.8×105

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Figure 17

Spanwise averaged ShC on the blade surface for various incidence angles at ReC,ex=1.8×105

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