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Research Papers

Tip-Shaping for HP Turbine Blade Aerothermal Performance Management

[+] Author and Article Information
Q. Zhang

University of Michigan–Shanghai Jiao Tong University,
Joint Institute,
Shanghai Jiao Tong University,
Shanghai 200240, China
e-mail: QZhang@sjtu.edu.cn

L. He

Department of Engineering Science,
University of Oxford,
Oxford OX2 0ES, UK
e-mail: Li.He@eng.ox.ac.uk

Contributed by the International Gas Turbine Institute (IGTI) of ASME for publication in the JOURNAL OF TURBOMACHINERY. Manuscript received October 14, 2012; final manuscript received October 16, 2012; published online June 28, 2013. Editor: David Wisler.

J. Turbomach 135(5), 051025 (Jun 28, 2013) (7 pages) Paper No: TURBO-12-1204; doi: 10.1115/1.4007896 History: Received October 14, 2012; Revised October 16, 2012

A large portion of the over-tip leakage flow is often transonic for a typical high pressure (HP) turbine blade. It has been observed that the tip heat transfer is noticeably lower in a high speed flow tip region than in a low speed region. The present study therefore investigates the feasibility of controlling blade heat transfer by tip shaping to locally accelerate the flow to a transonic regime. The results show that a significant heat load reduction can be achieved by the local flow acceleration. Such over-tip-shaping provides a great potential as an effective means to control heat load distribution (and hence thermal stress) over the blade tip surface. The feasibility of the concept and flow physics have been demonstrated in detail by CFD analyses, with and without the effect of moving casing. The experimental results obtained from a high speed linear cascade facility have also been presented. The novel tip-shaping concept proposed in this paper could provide a potential for promoting choking inside the tip gap as a new way to control the over-tip leakage mass flow.

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Figures

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Fig. 1

Tendency of a transonic over-tip leakage flow. (a) Typical surface pressure distribution for a turbine blade, and (b) Mach number contours on tip section and middle span section at a subsonic exit flow (Mexit = 0.5).

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Fig. 2

Computational domain and mesh employed in the present study

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Fig. 3

Schematic diagrams of the test section

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Fig. 4

Contours of (a) middle–gap Mach number, and (b) tip surface St numbers with streamlines

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Fig. 5

Shaped tip geometry employed in the present study

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Fig. 6

St number contours with different tip gaps (CFD)

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Fig. 7

Mach number distributions above the tip surface on a cut plane shown in Figs. 6(b), 6(c), and 6(e) (CFD)

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Fig. 8

Turbulent viscosity ratio (μTL) distributions on a cut plane shown in Figs. 6(b), 6(c), and 6(e) (CFD)

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Fig. 9

Measured St contours (a) flat tip with a tip gap ratio G = 1.5%, and (b) shaped tip with a minimum gap ratio Gmin of 1.0% and a gap ratio G of 1.5% for the rear region

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Fig. 10

Experimental results of circumferentially-averaged St number along axial direction for a flat tip and a shaped tip

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Fig. 11

St number distributions for a flat tip at three different tip gaps with a relatively moving casing (CFD)

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Fig. 12

A shaped tip geometry and corresponding St number distribution with a relatively moving casing. (Gmin = 0.5% and G = 1.5%)

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