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Research Papers

Overtip Shock Wave Structure and Its Impact on Turbine Blade Tip Heat Transfer

[+] Author and Article Information
Q. Zhang, D. O. O’Dowd, L. He, P. M. Ligrani

Department of Engineering Science, University of Oxford, Osney Mead, Oxford, OX2 0ES, UK

A. P. S. Wheeler

School of Engineering and Materials Science, Queen Mary, University of London, Mile End Road, London E1 4NS, UK

B. C. Y. Cheong

Turbine Systems (FH-3), Rolls-Royce plc., Bristol BS34 7QE, UK

J. Turbomach 133(4), 041001 (Apr 19, 2011) (8 pages) doi:10.1115/1.4002949 History: Received July 22, 2009; Revised May 21, 2010; Published April 19, 2011; Online April 19, 2011

In this paper, the transonic flow pattern and its influence on heat transfer on a high-pressure turbine blade tip are investigated using experimental and computational methods. Spatially resolved heat transfer data are obtained at conditions representative of a single-stage high-pressure turbine blade (Mexit=1.0, Reexit=1.27×106, gap=1.5% chord) using the transient infrared thermography technique within the Oxford high speed linear cascade research facility. Computational fluid dynamics (CFD) predictions are conducted using the Rolls-Royce HYDRA/PADRAM suite. The CFD solver is able to capture most of the spatial heat flux variations and gives prediction results, which compare well with the experimental data. The results show that the majority of the blade tip experiences a supersonic flow with peak Mach number reaching 1.8. Unlike other low-speed data in the open literature, the turbine blade tip heat transfer is greatly influenced by the shock wave structure inside the tip gap. Oblique shock waves are initiated near the pressure-side edge of the tip, prior to being reflected multiple times between the casing and the tip. Supersonic flow within the tip gap is generally terminated by a normal shock near the exit of the gap. Both measured and calculated heat transfer spatial distributions illustrate very clear stripes as the signature of the multiple shock structure. Overall, the supersonic part of tip experiences noticeably lower heat transfer than that near the leading-edge where the flow inside the tip gap remains subsonic.

Copyright © 2011 by American Society of Mechanical Engineers
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Figures

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Figure 6

Computational domain and mesh employed in the present study

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Figure 7

Isentropic Mach number distribution along the blade midspan and near tip region

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Figure 8

Local Mach number distribution along a cut plane in the middle of the tip gap clearance (HYDRA )

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Figure 9

Experimentally measured contours of heat transfer coefficient on a blade (W/m2 K)

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Figure 10

Tip leakage flow streamlines on a contour of tip surface pressure distribution (HYDRA ) (Pa)

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Figure 11

Experimentally obtained Contours of (a) adiabatic wall temperature and (b) tip surface temperature 8 s after heater mesh is turned on (°C)

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Figure 12

Contours of heat transfer coefficient on a blade tip predicted by HYDRA (W/m2 K)

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Figure 13

Comparisons of circumferential averaged heat transfer coefficient between experiment and HYDRA

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Figure 14

Heat flux contour obtained from (a) HYDRA and (b) experiment (W/m2)

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Figure 15

Tip surface heat flux (W/m2) and X-components of density gradient (kg/m2) distributions on four cut planes (HYDRA prediction)

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Figure 16

(a) Mach number, (b) pressure, and (c) turbulence-to-laminar viscosity ratio contours on a cut plane over the tip (HYDRA prediction)

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Figure 1

Schematic of the Oxford high speed linear cascade facility

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Figure 2

Schematic of the test section and instrumentation

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Figure 3

Inlet casing wall boundary-layer profile measured one axial chord upstream of the test blade

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Figure 4

Infrared camera in situ calibration during a blow-down run

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Figure 5

An example of heat flux versus temperature history at one location on the tip surface

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