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Research Papers

Unsteady Effects on Transonic Turbine Blade-Tip Heat Transfer

[+] Author and Article Information
Nicholas R. Atkins1

Whittle Laboratory,Department of Engineering,  University of Cambridge, Cambridge CB3 0DY, United Kingdomnra27@cam.ac.uk

Steven J. Thorpe

Department of Aeronautical and Automotive Engineering,  University of Loughborough, Leicestershire LE11 3TU, United Kingdoms.j.thorpe@lboro.ac.uk

Roger W. Ainsworth

Department of Engineering Science,  University of Oxford, Oxford OX1 3PJ, United Kingdomrog.ainsworth@stcatz.ox.ac.uk

1

Previous address: Department of Engineering Science, University of Oxford, Oxford OX1 3PJ, United Kingdom.

J. Turbomach 134(6), 061002 (Aug 27, 2012) (11 pages) doi:10.1115/1.4004845 History: Received July 11, 2011; Revised August 02, 2011; Published August 27, 2012; Online August 27, 2012

In a gas turbine engine the blade tips of the high-pressure turbine are exposed to high levels of convective heat transfer, because of the so-called tip-leakage phenomenon. The blade-lift distribution is known to control the flow distribution in the blade–tip gap. However, the interaction between upstream nozzle guide vanes and the rotor blades produces a time-varying flow field that induces varying flow conditions around the blade and within the tip gap. Extensive measurements of the unsteady blade-tip heat transfer have been made in an engine representative transonic turbine. These include measurements along the mean camber line of the blade tip, which have revealed significant variation in both time-mean and time-varying heat flux. The influences of potential interaction and the vane trailing edge have been observed. Numerical calculations of the turbine stage using a Reynolds-averaged-Navier-Stokes-based computational fluid dynamics code have also been conducted. In combination with the experimental results, these have enabled the time-varying flow field to be probed in the blade-relative frame of reference. This has allowed a deeper analysis of the unsteady heat-transfer data, and the quantification of the impact of vane potential field and vane trailing edge interaction on the tip-region flow and heat transfer. In particular, the separate effects of time-varying flow temperature and heat-transfer coefficient have been established.

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Copyright © 2012 by American Society of Mechanical Engineers
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Figures

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Figure 1

The Oxford Rotor Stage

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Figure 2

Schematic of the ORF stage geometry

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Figure 3

(a) Instrumented blade tip with 17 thin-film gauges positioned along the mean camber line, and (b) CFD blade-tip surface nodes superimposed onto the instrumented blade tip to show the position of the virtual gauge points

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Figure 4

The computational domain

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Figure 5

Detail of the tip-gap mesh topology

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Figure 6

Comparison of measured and predicted unsteady blade-tip heat flux across three vane periods at 13 gauge locations distributed along the mean camberline

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Figure 7

Instantaneous snapshots of the blade-tip flow field across two vane passing cycles. Contours of: heat-flux, q· (first row), static-pressure, p (second row), recovery temperature, Trec (third row), and Nusselt number (fourth row). NB vane spacing not to scale for clarity.

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Figure 8

(top) Unsteady heat flux at gauge position 2, (middle) variation of unsteady driver temperature and Nusselt number with vane phase, and (bottom) isentropic component of Trec modulation, based on surface static pressure changes

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Figure 9

(upper) Unsteady heat flux at gauge position 5, and (lower) variation of unsteady driver temperature and Nusselt number with vane phase

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Figure 10

(upper) Unsteady heat flux at gauge position 7, and (lower) variation of unsteady driver temperature and Nusselt number with vane phase

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Figure 11

Static pressure contours showing the variation of temporal pressure gradient adjacent to the early PS

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Figure 12

Time points for each of the instantaneous snapshots in Fig. 1

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Figure 13

Static pressure contours showing the variation of temporal pressure gradient as the blade passes the vane TE

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Figure 14

Time points for each of the instantaneous snapshots in Fig. 1

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