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Research Papers

Effects of Endwall Motion on the Aero-Thermal Performance of a Winglet Tip in a HP Turbine

[+] Author and Article Information
Chao Zhou

 State Key Laboratory for Turbulence and Complex Systems, College of Engineering, Peking University, Beijing, 100871 Chinaczhou@pku.edu.cn

Howard Hodson

Whittle Laboratory, Department of Engineering,  University of Cambridge, Cambridge, CB3 0FY, UK

Ian Tibbott, Mark Stokes

 Rolls-Royce plc, Derby, DE24 8BJ, UK

J. Turbomach 134(6), 061036 (Sep 17, 2012) (12 pages) doi:10.1115/1.4006302 History: Received July 23, 2011; Revised July 26, 2011; Published September 17, 2012

In a gas turbine, the casing endwall moves relative to the blades. In this paper, numerical methods are first validated using experimental results for a stationary endwall. They are then used to study the effects of endwall motion on the aero-thermal performance of both winglet tips with and without tip film cooling at a tip gap of 1.9% C. The endwall motion imposes a tangential force on the flow. A scraping vortex is formed and the flow pattern within the tip gap changes significantly. The tip leakage mass flow rate that exits the tip gap from the suction side edge reduces by about 42% with endwall motion. Overall, the endwall motion reduces the tip leakage loss by 15%. The flow field downstream of the cascade also changes with endwall motion. With endwall motion, the changed flow pattern within the tip gap significantly changes the distribution of the Nusselt number on the winglet tip. For the winglet tip without tip film cooling, the Nusselt number and the heat load decrease with endwall motion. This is mainly due to the reduction in the tip leakage mass flow ratio, which reduces the leakage velocity over the tip. On the winglet tip with tip film cooling, the cooling effectiveness increases by 9% with endwall motion. Combined with the reduced Nusselt number, the heat flux on the winglet tip with tip film cooling reduces by 31% with endwall motion. The cooling effectiveness on the near tip region of the pressure side remains almost unchanged, however, the heat flux rate in this area reduces. This is because the reduced tip leakage mass flow ratio reduces the Nusselt number. With the moving endwall, the thermal performance of the suction side surface of the blade is affected by the scraping vortex. The effects of endwall motion should be considered during the design of the blade tip.

Copyright © 2012 by American Society of Mechanical Engineers
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References

Figures

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Figure 18

Static pressure distribution of the winglet tip; CFD

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Figure 19

Nusselt number on the winglet tip; CFD

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Figure 20

Distribution of the Nusselt number on surfaces of the winglet tip; CFD

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Figure 11

Leakage mass flow rate per unit area that exits the gap; winglet tip without tip film cooling, CFD

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Figure 22

Cooling effectiveness on blade surfaces; CFD

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Figure 12

Velocity distribution in middle of tip gap; CFD

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Figure 24

Heat flux rate hrate of the winglet tip with tip film cooling; CFD

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Figure 1

Layout of cascade

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Figure 2

Geometry of winglet tip with tip film cooling

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Figure 3

Mesh of winglet tip without tip film cooling

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Figure 4

Mesh of winglet tip with tip film cooling

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Figure 5

Mid-span Cp distribution; CFD

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Figure 6

Cp distribution on endwall, winglet tip, τ = 1.9% C, stationary endwall

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Figure 7

Endwall Cp distribution at line ‘A’ of Fig. 6, winglet tip, stationary endwall, exp

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Figure 8

Tip leakage loss of winglet tip; stationary endwall

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Figure 9

Cooling effectiveness of winglet tip with tip film cooling; stationary endwall

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Figure 10

Velocity triangle

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Figure 23

Cooling effectiveness; CFD; view from the leading edge (see Fig. 2)

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Figure 13

Velocity vectors at the cut plane of Fig. 12(a); CFD

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Figure 14

Stagnation pressure coefficient at the cut planes; CFD

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Figure 15

Cp,0-Cp,0_prof in the spanwise direction, 15% Cx downstream; CFD

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Figure 16

Deviation of the yaw angle relative to midspan in the spanwise direction, 15%Cx downstream; CFD

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Figure 17

Velocity vector and 2D flow path lines near the suction side winglet; view of plane ‘1’ in Fig. 1 and 24%Cx ; CFD

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Figure 21

Cooling effectiveness on the winglet tip with tip film cooling; CFD

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