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Research Papers

# Aerothermal Investigations of Tip Leakage Flow in Axial Flow Turbines—Part II: Effect of Relative Casing Motion

[+] Author and Article Information
S. K. Krishnababu1

Department of Engineering, University of Cambridge, Cambridge CB2 1TN, UK

W. N. Dawes, H. P. Hodson

Department of Engineering, University of Cambridge, Cambridge CB2 1TN, UK

G. D. Lock

Department of Mechanical Engineering, University of Bath, Bath BA2 7AY, UK

J. Hannis

Siemens Industrial Turbomachinery Ltd., P.O. Box 1, Waterside South, Lincoln LN5 7FD, UK

C. Whitney2

Alstom Power Technology Centre, Cambridge Road, Whetstone, Leicester LE8 6LH, UK

1

Present address: VUTC, Department of Mechanical Engineering, Imperial College, London, UK.

2

J. Turbomach 131(1), 011007 (Oct 03, 2008) (10 pages) doi:10.1115/1.2952378 History: Received August 27, 2007; Revised January 04, 2008; Published October 03, 2008

## Abstract

A numerical study has been performed to investigate the effect of casing motion on the tip leakage flow and heat transfer characteristics in unshrouded axial flow turbines. The relative motion between the blade tip and the casing was simulated by moving the casing in a direction from the suction side to the pressure side of the stationary blade. Base line flat tip geometry and squealer type geometries, namely, double squealer or cavity and suction side squealer, were considered at a clearance gap of $1.6%C$. The computations were performed using a single blade with periodic boundary conditions imposed along the boundaries in the pitchwise direction. Turbulence was modeled using the shear stress transport $k-ω$ model. The flow conditions correspond to an exit Reynolds number of $2.3×105$. The results were compared to those obtained without the relative casing motion reported in Part I of this paper. In general, the effect of relative casing motion was to decrease the tip leakage mass flow and the average heat transfer to the tip due to the decrease in leakage flow velocity caused by a drop in driving pressure difference. Compared to the computations with stationary casing, in the case of all the three geometries considered, the average heat transfer to the suction surface of the blade was found to be larger in the case of the computations with relative casing motion. At a larger clearance gap of $2.8%C$, in case of a flat tip, while the tip leakage mass flow decreased due to relative casing motion, only a smaller change in the average heat transfer to the tip and the suction surface of the blade was noticed.

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## Figures

Figure 1

Computational domain with a typical mesh superimposed

Figure 2

Validation study: Contours of heat transfer coefficient on tip: (a) experimental, (b) G1, (c) G2, and (d) G3

Figure 3

Figure 4

Streamlines across flat tip at H of 1.6%C: (a) stationary casing and (b) with casing motion

Figure 5

Contours of h on flat tip: (a) stationary casing and (b) with casing motion

Figure 6

Contours of h on flat tip blade with H∕C of (a) 1.6% and (b) 2.8%—region near the tip

Figure 7

Contours of total pressure loss coefficient on an axial plane at x∕Cx=0.7: Flat tip with H∕C of (a) 1.6% and (b) 2.8%—region near the tip

Figure 8

Streamlines across squealer tips with H∕C of 1.6%: (a) stationary casing and (b) with casing motion

Figure 9

Contours of h on squealer tips with H∕C of 1.6%: (a) stationary casing and (b) with casing motion

Figure 10

Contours of h on squealer tips with H∕C of 1.6%: (a) cavity tip and (b) SSS tip—region near the tip

Figure 11

Contours of total pressure loss coefficient on an axial plane at x∕Cx=0.7: Squealer tips with H∕C of 1.6%: (a) cavity tip and (b) SSS tip

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