Heat Transfer and Aerodynamics of Turbine Blade Tips in a Linear Cascade

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

Department of Mechanical Engineering, University of Bath, Bath, UK

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

Department of Engineering, University of Cambridge, Cambridge, UK

J. Hannis

 Siemens Industrial Turbomachinery Ltd., Lincoln, UK

C. Whitney

 Alstom Power Technology Centre, Leicester, UK

J. Turbomach 128(2), 300-309 (Mar 01, 2004) (10 pages) doi:10.1115/1.2137745 History: Received October 01, 2003; Revised March 01, 2004

Local measurements of the heat transfer coefficient and pressure coefficient were conducted on the tip and near tip region of a generic turbine blade in a five-blade linear cascade. Two tip clearance gaps were used: 1.6% and 2.8% chord. Data was obtained at a Reynolds number of 2.3×105 based on exit velocity and chord. Three different tip geometries were investigated: A flat (plain) tip, a suction-side squealer, and a cavity squealer. The experiments reveal that the flow through the plain gap is dominated by flow separation at the pressure-side edge and that the highest levels of heat transfer are located where the flow reattaches on the tip surface. High heat transfer is also measured at locations where the tip-leakage vortex has impinged onto the suction surface of the aerofoil. The experiments are supported by flow visualization computed using the CFX CFD code which has provided insight into the fluid dynamics within the gap. The suction-side and cavity squealers are shown to reduce the heat transfer in the gap but high levels of heat transfer are associated with locations of impingement, identified using the flow visualization and aerodynamic data. Film cooling is introduced on the plain tip at locations near the pressure-side edge within the separated region and a net heat flux reduction analysis is used to quantify the performance of the successful cooling design.

Copyright © 2006 by American Society of Mechanical Engineers
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Figure 10

Uncooled tip NHFR for H∕C=1.6%

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Figure 11

(a)–(c). Cooled Tip h, η and NHFR

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Figure 12

CFD predictions of h(W∕m2K) for plain tip, H∕C=1.6%

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Figure 9

Heat transfer coefficient for plain (top pair), squealer (middle) and cavity (bottom) geometries (W∕m2K)

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Figure 8

Heat transfer coefficients for plain tip geometry: Top H∕C 1.6%, bottom H∕C=2.8%

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Figure 7

CFX flow visualization

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Figure 6

Cross-chord measurements of Cp and h at x∕C=50%H∕C=1.6%

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Figure 5

Cp Contours as measured on the casing

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Figure 4

Cp Contours as measured on the blade and tip

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Figure 2

Definition of blade parameters

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Figure 1

Low speed cascade modified for heat transfer measurements



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