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Research Papers

# Aerothermal Investigations of Tip Leakage Flow in Axial Flow Turbines—Part I: Effect of Tip Geometry and Tip Clearance Gap

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

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

P. J. Newton, G. D. Lock

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

W. N. Dawes, H. P. Hodson

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

J. Hannis

Siemens Industrial Turbomachinery Ltd., Lincoln LN5 7FD, UK

C. Whitney2

Alstom Power Technology Centre, LN5 7SD, UK

1

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

2

J. Turbomach 131(1), 011006 (Oct 03, 2008) (14 pages) doi:10.1115/1.2950068 History: Received June 30, 2007; Revised January 04, 2008; Published October 03, 2008

## Abstract

A numerical study has been performed to investigate the effect of tip geometry on the tip leakage flow and heat transfer characteristics in unshrouded axial flow turbines. Base line flat tip geometry and squealer type geometries, namely, double squealer or cavity and suction-side squealer, were considered. The performances of the squealer geometries, in terms of the leakage mass flow and heat transfer to the tip, were compared with the flat tip at two different tip clearance gaps. The computations were performed using a single blade with periodic boundary conditions imposed along the boundaries in the pitchwise direction. Turbulence was modeled using three different models, namely, standard $k-ε$, low Re $k-ω$, and shear stress transport (SST) $k-ω$, in order to assess the capability of the models in correctly predicting the blade heat transfer. The heat transfer and static pressure distributions obtained using the SST $k-ω$ model were found to be in close agreement with the experimental data. It was observed that compared to the other two geometries considered, the cavity tip is advantageous both from the aerodynamic and from the heat transfer perspectives by providing a decrease in the amount of leakage, and hence losses, and average heat transfer to the tip. In general, for a given geometry, the leakage mass flow and the heat transfer to the tip increased with increase in tip clearance gap. Part II of this paper examines the effect of relative casing motion on the flow and heat transfer characteristics of tip leakage flow. In Part III of this paper the effect of coolant injection on the flow and heat transfer characteristics of tip leakage flow is presented.

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## Figures

Figure 1

A schematic of tip leakage flow

Figure 2

Computational domain with a typical mesh superimposed

Figure 3

Grid independence study: contours of heat transfer coefficient on flat tip with H∕C of 1.6%: (a) experiment, (b) G1, (c) G2, and (d) G3 using SST k-ω

Figure 4

Figure 5

Dependence of h on turbulence model: contours of h on flat tip with H∕C of 1.6% as predicted by (a) k-ε, (b) k-ω, (c) SST k-ω models, and (d) experiment

Figure 6

Contours of turbulence kinetic energy on flat tip with H∕C of 1.6% as predicted by (a) k-ε, (b) k-ω, and (c) SST k-ω models using Mesh G2

Figure 7

Flow pattern across tip using SST k-ω model: flat tip with H∕C of (a) 1.6% and (b) 2.8%

Figure 8

Contours of Cp on tip: flat tip with H∕C of (a) 1.6% and (b) 2.8%

Figure 9

Contours of h on tip: flat tip with H∕C of (a) 1.6% and (b) 2.8%

Figure 10

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

Figure 11

Computational domain: cavity tip

Figure 12

Flow pattern across tip: cavity tip with H∕C of (a) 1.6% and (b) 2.8%

Figure 13

Contours of Cp on tip: cavity tip with H∕C of (a) 1.6% and (b) 2.8%

Figure 14

Contours of h on tip: cavity tip with H∕C of (a) 1.6% and (b) 2.8%

Figure 15

Computed contours of h on blade: cavity tip with H∕C of (a) 1.6% and (b) 2.8%—region near the tip

Figure 16

Computational domain: SSS tip

Figure 17

Flow pattern across tip: SSS tip with H∕C of (a) 1.6% and (b) 2.8%

Figure 18

Contours of Cp on tip: SSS tip with H∕C of (a) 1.6% and (b) 2.8%C

Figure 19

Contours of h on tip: SSS tip with H∕C of (a) 1.6% and (b) 2.8%

Figure 20

Computed contours of h on blade: SSS tip with H∕C of (a) 1.6% and (b) 2.8%—region near the tip

Figure 21

Contours of total pressure loss coefficient on an axial plane at x∕Cx of 0.5: region near the tip gap: (a) flat tip, (b) cavity tip, and (c) SSS tip with H∕C of 1.6%

Figure 22

Variation of mass averaged Yp along the axial direction

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