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Research Papers

Aerothermal Investigation of Tip Leakage Flow in a Film Cooled Industrial Turbine Rotor

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

Department of Engineering, University of Cambridge, Madingley Road, Cambridge CB3 0DS, UK

H. P. Hodson

Department of Engineering, University of Cambridge, Madingley Road, Cambridge CB3 0DS, UK

G. D. Booth2

 SIEMENS Industrial Turbomachinery Ltd, Lincoln LN5 7FD, UK

G. D. Lock

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

W. N. Dawes

Department of Engineering,University of Cambridge

1

Present address: Siemens Industrial Turbomachinery Ltd, Lincoln, UK.

2

Present address: Doosan Babcock Energy Ltd, Renfrew, UK.

J. Turbomach 132(2), 021016 (Jan 20, 2010) (9 pages) doi:10.1115/1.3144164 History: Received June 19, 2008; Revised February 22, 2009; Published January 20, 2010; Online January 20, 2010

A numerical investigation of the flow and heat transfer characteristics of tip leakage in a typical film cooled industrial gas turbine rotor is presented in this paper. The computations were performed on a rotating domain of a single blade with a clearance gap of 1.28% chord in an engine environment. This standard blade featured two coolant and two dust holes, in a cavity-type tip with a central rib. The computations were performed using CFX 5.6 , which was validated for similar flow situations by Krishnababu (2007, “Aero-Thermal Investigation of Tip Leakage Flow in Axial Flow Turbines: Part I—Effect of Tip Geometry,” ASME Paper No. 2007-GT-27954). These predictions were further verified by comparing the flow and heat transfer characteristics computed in the absence of coolant ejection with computations previously performed in the company (SIEMENS) using standard in-house codes. Turbulence was modeled using the shear-stress transport (SST) k-ω turbulence model. The comparison of calculations performed with and without coolant ejection has shown that the coolant flow partially blocks the tip gap, resulting in a reduction in the amount of mainstream leakage flow. The calculations identified that the main detrimental heat transfer issues were caused by impingement of the hot leakage flow onto the tip. Hence three different modifications (referred as Cases 1–3) were made to the standard blade tip in an attempt to reduce the tip gap exit mass flow and the associated impingement heat transfer. The improvements and limitations of the modified geometries, in terms of tip gap exit mass flow, total area of the tip affected by the hot flow and the total heat flux to the tip, are discussed. The main feature of the Case 1 geometry is the removal of the rib, and this modification was found to effectively reduce both the total area affected by the hot leakage flow and total heat flux to the tip, while maintaining the same leakage mass flow as the standard blade. Case 2 featured a rearrangement of the dust holes in the tip, which, in terms of aerothermal dynamics, proved to be marginally inferior to Case 1. Case 3, which essentially created a suction-side squealer geometry, was found to be inferior even to the standard cavity-tip blade. It was also found that the hot spots, which occur in the leading edge region of the standard tip, and all modifications contributed significantly to the area affected by the hot tip leakage flow and the total heat flux.

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Copyright © 2010 by American Society of Mechanical Engineers
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Figures

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Figure 1

Computational domain

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Figure 2

Typical mesh used in the computations

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Figure 3

(a) Contours of heat transfer coefficient on the tip and (b) Variation in heat transfer coefficient at midspan

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Figure 4

(a) Contours of h on tip with streamlines superimposed and (b) contours of h on tip

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Figure 5

Flow conditions at inlet to dust and coolant holes

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Figure 6

(a) Contours of HFR on tip with streamlines superimposed and (b) contours of HFR on tip

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Figure 7

(a) Contours of HFR on blade with streamlines superimposed and (b) contours of HFR on blade showing foot print of the tip leakage vortex

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Figure 8

(a) Contours of HFR on tip and (b) contours of HFR on tip with streamlines superimposed: Case 1

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Figure 9

Schematic of Case 2 tip (derived from Case 1 tip)

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Figure 10

(a) Contours of HFR on tip and (b) contours of HFR on tip with streamlines superimposed: Case 2

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Figure 11

Contours of HFR on blade (a) view from PS and (b) view from SS: Case 2

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Figure 12

Suction-side squealer tip (Case 3)

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Figure 13

(a) Contours of HFR on tip with streamlines superimposed and (b) contours of HFR on tip: Case 3

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