Research Papers

Tip-Leakage Losses in Subsonic and Transonic Blade Rows

[+] Author and Article Information
Andrew P. S. Wheeler

Engineering and the Environment
University of Southampton
Highfield, Southampton
United Kingdom
e-mail: a.wheeler@soton.ac.uk

Shashimal Banneheke

School of Engineering and Materials Science
Queen Mary
University of London
United Kingdom

1Corresponding author

Contributed by the International Gas Turbine Institute (IGTI) of ASME for publication in the JOURNAL OF TURBOMACHINERY. Manuscript received August 1, 2011; final manuscript received August 8, 2011; published online October 30, 2012. Editor: David Wisler.

J. Turbomach 135(1), 011029 (Oct 30, 2012) (7 pages) Paper No: TURBO-11-1171; doi: 10.1115/1.4006424 History: Received August 01, 2011; Revised August 08, 2011

In this paper the effect of blade-exit Mach number on unshrouded turbine tip-leakage flows is investigated. Previously published experimental data of a high-pressure turbine blade are used to validate a computational fluid dynamics (CFD) code, which is then used to study the tip-leakage flow at blade-exit Mach numbers from 0.6 to 1.4. Three-dimensional (3D) calculations are performed of a flat-tip and a cavity-tip blade. Two-dimensional calculations are also performed to show the effect of various squealer-tip geometries on an idealized tip flow. The results show that as the blade-exit Mach number is increased the tip-leakage flow becomes choked. Therefore the tip-leakage flow becomes independent of the pressure difference across the tip and hence the blade loading. Thus the effect of the tip-leakage flow on overall blade loss reduces at blade-exit Mach numbers greater than 1.0. The results suggest that for transonic blade rows it should be possible to raise blade loading within the tip region without increasing tip-leakage loss.

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Fig. 1

Schematic of subsonic and transonic tip flows

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Fig. 2

Midspan Mach number distribution at Mexit = 0.8 for the Kiock et al. blade

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Fig. 3

Cascade blade computational geometries

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Fig. 4

2D computational domain and geometries tested

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Fig. 5

Variation of blade loss coefficient and exit angle with Mach number

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Fig. 6

Contours of Mach number at midspan with different exit Mach numbers

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Fig. 7

Contours of Mach number within the aft portion of the tip at different axial stations

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Fig. 8

Variation of Mach number along a midgap contour around the tip, and along a free-stream contour at 90% span and 5% chord away from the blade surface (flat-tip blade)

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Fig. 9

Schematic of idealized choked tip flow

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Fig. 10

Predicted discharge coefficients for 2D idealized tip flows (w/g = 10)

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Fig. 11

Predicted Mach number contours for 2D flat-tip and pressure-side squealer-tip flows (w/g = 10)

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Fig. 12

Variation of tip-leakage mass-flow rate with blade-exit Mach number for the flat-tip and cavity-tip blades

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Fig. 13

Spanwise profiles of blade-exit loss coefficient for flat-tip blade

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Fig. 14

Variation of tip-loss coefficient (ξtip = ξ−ξ0) with Mexit




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