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Research Papers

Aerothermal Investigations of Tip Leakage Flow in Axial Flow Turbines—Part III: TIP Cooling

[+] Author and Article Information
P. J. Newton, G. D. Lock

Department of Mechanical Engineering, University of Bath, Bath BA2 7AY, UK

S. K. Krishnababu, H. P. Hodson, W. N. Dawes

Whittle Laboratory, Department of Engineering, University of Cambridge, Cambridge CB2 1PZ, UK

J. Hannis

 Siemens Industrial Turbomachinery Ltd., Lincoln LN5 7FD, UK

C. Whitney

 Alstom Power Technology Centre, Leicester LN5 7FD, UK

J. Turbomach 131(1), 011008 (Oct 03, 2008) (12 pages) doi:10.1115/1.2950060 History: Received June 14, 2007; Revised July 05, 2007; Published October 03, 2008

Contours of heat transfer coefficient and effectiveness have been measured on the tip of a generic cooled turbine blade, using the transient liquid crystal technique. The experiments were conducted at an exit Reynolds number of 2.3×105 in a five-blade linear cascade with tip clearances of 1.6% and 2.8% chord and featuring engine-representative cooling geometries. These experiments were supported by oil-flow visualization and pressure measurements on the tip and casing and by flow visualization calculated using CFX , all of which provided insight into the fluid dynamics within the gap. The data were compared with measurements taken from the uncooled tip gap, where the fluid dynamics is dominated by flow separation at the pressure-side edge. Here, the highest levels of heat transfer are located where the flow reattaches on the tip surface downstream of the separation bubble. A quantitative assessment using the net heat flux reduction (NHFR) revealed a significant benefit of ejecting coolant inside this separation bubble. Engine-representative blowing rates of approximately 0.6–0.8 resulted in good film-cooling coverage and a reduction in heat flux to the tip when compared to both the flat tip profile and the squealer and cavity tip geometries discussed in Part 1 of this paper. Of the two novel coolant-hole configurations studied, injecting the coolant inside the separation bubble resulted in an improved NHFR when compared to injecting coolant at the location of reattachment.

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Copyright © 2009 by American Society of Mechanical Engineers
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Figures

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Figure 1

Low-speed cascade modified for heat transfer measurements

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Figure 2

Cooled blade subassembly

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Figure 3

(a) Pressure coefficient for tip and aerofoil surfaces—colored version available in Ref. 24. (b) Heat transfer coefficient (Wm−2K−1) for tip and aerofoil surfaces—colored version available in Ref. 24.

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Figure 4

((a) and (b)) Oil-flow visualization and pressure coefficient on casing—colored version available in Ref. 24. ((c) and (d)) CFX streamlines and heat transfer coefficient (Wm−2K−1) on tip—colored version available in Ref. 24.

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Figure 5

((a) and (b)) NHFR for SS squealer and cavity tips—colored version available in Ref. 24

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Figure 6

Casing Cp for first (a) and second (b) cooling configurations—colored version available in Ref. 24

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Figure 7

((a)–(c)) Pressure coefficient on casing for B=0.6, 0.8, and 1.0, second cooling configuration—colored version available in Ref. 24

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Figure 8

Oil-flow visualization on tip: first cooling geometry, xc∕C=2.2%—colored version available in Ref. 24

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Figure 12

Cooled tip xc∕C=4.4%, h, η, NHFR, and B¯=0.8—colored version available in Ref. 24

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Figure 10

Cooled tip xc∕C=2.2%, h, η, NHFR, and B¯=0.58—colored version available in Ref. 24

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Figure 9

Cooled tip xc∕C=2.2%, h, η, NHFR, and B¯=0.74—colored version available in Ref. 24

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Figure 11

Cooled tip xc∕C=2.2%, h, η, NHFR, and B¯=0.99—colored version available in Ref. 24

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