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Research Papers

Heat Transfer and Film Cooling of Blade Tips and Endwalls

[+] Author and Article Information
S. Naik

 Alstom Power, 5401 Baden, Switzerlandshailendra.naik@power.alstom.com

C. Georgakis

 Alstom Power, Rugby CV21 2NH, UK

T. Hofer

 von Kármán Institute for Fluid Dynamics, B-1640 Rhode-Saint-Genése, Belgium

D. Lengani1

 von Kármán Institute for Fluid Dynamics, B-1640 Rhode-Saint-Genése, Belgium

1

Present address: Graz University of Technology, Graz, Austria.

J. Turbomach 134(4), 041004 (Jul 19, 2011) (11 pages) doi:10.1115/1.4003652 History: Received July 02, 2010; Revised August 03, 2010; Published July 19, 2011; Online July 19, 2011

This paper investigates the flow, heat transfer, and film cooling effectiveness of advanced high pressure turbine blade tips and endwalls. Two blade tip configurations have been studied, including a full rim squealer and a partial squealer with leading edge and trailing edge cutouts. Both blade tip configurations have pressure side film cooling and cooling air extraction through dust holes, which are positioned along the airfoil camber line on the tip cavity floor. The investigated clearance gap and the blade tip geometry are typical of that commonly found in the high pressure turbine blades of heavy-duty gas turbines. Numerical studies and experimental investigations in a linear cascade have been conducted at a blade exit isentropic Mach number of 0.8 and a Reynolds number of 9×105. The influence of the coolant flow ejected from the tip dust holes and the tip pressure side film holes has also been investigated. Both the numerical and experimental results showed that there is a complex aerothermal interaction within the tip cavity and along the endwall. This was evident for both tip configurations. Although the global heat transfer and film cooling characteristics of both blade tip configurations were similar, there were distinct local differences. The partial squealer exhibited higher local film cooling effectiveness at the trailing edge but also low values at the leading edge. For both tip configurations, the highest heat transfer coefficients were located on the suction side rim within the midchord region. However, on the endwall, the highest heat transfer rates were located close to the pressure side rim and along most of the blade chord. Additionally, the numerical results also showed that the coolant ejected from the blade tip dust holes partially impinges onto the endwall.

Copyright © 2012 by American Society of Mechanical Engineers
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Figures

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Figure 1

Investigated blade tip geometries: (a) full rim squealer and (b) partial double-sided squealer

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Figure 2

Location of instrumentation on tip and endwall: (a) pressure taps on the full squealer tip, (b) pressure taps on the partial squealer, (c) thin film gauges on the full squealer tip, (d) thin film gauges on the partial squealer tip, (e) pressure taps and/or thin film gauges on the endwall, and (f) endwall heat transfer model

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Figure 3

Computational grid of the full squealer geometry

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Figure 4

Experimental and numerical study pressure and temperature inlet boundary conditions

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Figure 5

Pressure profile around the airfoil tip region

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Figure 6

Predicted squealer tip and endwall pressure distribution

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Figure 7

Comparison of pressure distribution at the (a) squealer rim surfaces and (b) on the cavity bottom floor

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Figure 8

Pressure distributions on the endwall

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Figure 9

Flow structure and Mach number distribution of the full squealer geometry

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Figure 10

Flow visualization on the squealer tip and the endwall from the experimental cascade (11-12)

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Figure 11

Heat transfer coefficient on the squealer tip and endwall surface: (a) coolant ratio mc/mg=0.48 and (b) coolant ratio mc/mg=0.22

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Figure 12

Comparison of heat transfer coefficient values on (a) the squealer rim and (b) cavity bottom surfaces for a coolant flow ratio mc/mg=0.48%

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Figure 13

Measured endwall heat transfer distribution: (a) no coolant injection, (b) minimum coolant injection, and (c) maximum coolant injection

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Figure 14

Comparison of heat transfer coefficient on endwall

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Figure 15

Contours of film cooling effectiveness η (on squealer and endwall (mc/mg=0.48))

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Figure 16

Flow structure and coolant flow trajectories for the high coolant ejection ratio conditions (mc/mg=0.48)

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Figure 17

Surface mesh and geometry of the double-sided partial rim squealer tip

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Figure 18

Near blade tip and endwall predicted pressure distribution for the partial squealer

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Figure 19

Measured oil flow paths on the partial squealer tip and the endwall (11-12)

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Figure 20

Comparison of pressure distribution on (a) squealer rim, (b) the cavity floor bottom floor, and (c) endwall

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Figure 21

Contours of heat transfer coefficient on the partial squealer and endwall with a coolant flow ratio, mc/mg=0.48%

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Figure 22

Measured and predicted tip and endwall heat transfer coefficients: (a) squealer rim, (b) cavity bottom floor, and (c) tip endwall

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Figure 23

Contours of film cooling effectiveness η on partial squealer tip and endwall surface

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Figure 24

General flow structure of the partial squealer tip

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