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Research Papers

Computational Modeling of Tip Heat Transfer to a Superscale Model of an Unshrouded Gas Turbine Blade

[+] Author and Article Information
Brian M. T. Tang

Department of Engineering Science, University of Oxford, Parks Road, Oxford OX1 3PJ, UKbrian.tang@eng.ox.ac.uk

Pepe Palafox1

Department of Engineering Science, University of Oxford, Parks Road, Oxford OX1 3PJ, UK

Brian C. Y. Cheong

Rolls-Royce plc., Turbine Systems (FH-3), Bristol BS34 7QE, UKbrian.cheong@rolls-royce.com

Martin L. G. Oldfield

Department of Engineering Science, University of Oxford, Parks Road, Oxford OX1 3PJ, UKmartin.oldfield@eng.ox.ac.uk

David R. H. Gillespie

Department of Engineering Science, University of Oxford, Parks Road, Oxford OX1 3PJ, UKdavid.gillespie@eng.ox.ac.uk

1

Present address: GE Corporate Research, Schnectady, NY 12309.

J. Turbomach 132(3), 031023 (Apr 07, 2010) (8 pages) doi:10.1115/1.3153307 History: Received March 02, 2009; Revised March 16, 2009; Published April 07, 2010; Online April 07, 2010

Control of over-tip leakage flow between turbine blade tips and the stationary shroud is one of the major challenges facing gas turbine designers today. The flow imposes large thermal loads on unshrouded high pressure (HP) turbine blades and is significantly detrimental to turbine blade life. This paper presents results from a computational study performed to investigate the detailed blade tip heat transfer on a sharp-edged, flat tip HP turbine blade. The tip gap is engine representative at 1.5% of the blade chord. Nusselt number distributions on the blade tip surface have been obtained from steady flow simulations and are compared with experimental data carried out in a superscale cascade, which allows detailed flow and heat transfer measurements in stationary and engine representative conditions. Fully structured, multiblock hexahedral meshes were used in the simulations performed in the commercial solver FLUENT . Seven industry-standard turbulence models and a number of different tip gridding strategies are compared, varying in complexity from the one-equation Spalart–Allmaras model to a seven-equation Reynolds stress model. Of the turbulence models examined, the standard k-ω model gave the closest agreement to the experimental data. The discrepancy in Nusselt number observed was just 5%. However, the size of the separation on the pressure side rim was underpredicted, causing the position of reattachment to occur too close to the edge. Other turbulence models tested typically underpredicted Nusselt numbers by around 35%, although locating the position of peak heat flux correctly. The effect of the blade to casing motion was also simulated successfully, qualitatively producing the same changes in secondary flow features as were previously observed experimentally, with associated changes in heat transfer with the blade tip.

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Copyright © 2010 by American Society of Mechanical Engineers
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References

Figures

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Figure 1

Schematic of the linear cascade

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Figure 2

Layers comprising the 210 μm thick blade tip

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Figure 3

Computational domain

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Figure 4

Detail of blade tip mesh with mesh cut-planes (“fine (adjusted)” mesh shown)

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Figure 5

Tip gap mesh refinement comparison

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Figure 6

Pathlines of flow over blade tip

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Figure 7

Velocity (m s−1) contours through the tip gap on a transverse plane

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Figure 8

Effect of grid size on Nusselt number distributions

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Figure 9

Nusselt number distributions showing the effect of the moving endwall

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Figure 10

Comparison of predicted blade tip Nusselt number distributions using different turbulence models with the experimental data

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Figure 11

Percentage difference between predicted and experimentally measured blade tip Nusselt number distributions using different turbulence models

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Figure 12

Turbulent viscosity (Pa s) at the tip gap midplane

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Figure 13

Mean absolute error in Nu

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