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Research Papers

The Tip Leakage Flow of an Unshrouded High Pressure Turbine Blade With Tip Cooling

[+] Author and Article Information
Chao Zhou

Whittle Laboratory, Department of Engineering,  University of Cambridge, CB3 0DY Cambridge, UKchao.zhou@cantab.net

Howard Hodson

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

J. Turbomach 133(4), 041028 (Apr 27, 2011) (12 pages) doi:10.1115/1.4001174 History: Received July 20, 2009; Revised July 28, 2009; Published April 27, 2011; Online April 27, 2011

Experimental, analytical, and numerical methods have been employed to study the aerodynamic performance of four different cooled tips with coolant mass ratios between 0% and 1.2% at three tip gaps of 1%, 1.6%, and 2.2% of the chord. The four cooled tips are two flat tips with different coolant holes, a cooled suction side squealer tip and a cooled cavity tip. Each tip has ten coolant holes with the same diameter. The uncooled cavity tip produces the smallest loss among all uncooled tips. On the cooled flat tip, the coolant is injected normally into the tip gap and mixes directly with flow inside the tip gap. The momentum exchange between the coolant and the flow that enters the tip gap creates significant blockage. As the coolant mass flow ratio increases, the tip leakage loss of the cooled flat tip first decreases and then increases. For the cooled cavity tip, the blockage effect of the coolant is not as big as that on the cooled flat tip. This is because after the coolant exits the coolant holes, it mixes with flow in the cavity first and then mixes with tip flow in the tip gap. The tip leakage loss of the cooled cavity tip increases as the coolant mass flow ratio increase. As a result, at a tip gap of 1.6% of the chord, the cooled cavity tip gives the lowest loss. At the smallest tip gap of 1% of the chord, the cooled flat tip produces less loss than the cooled cavity tip when the coolant mass flow ratios larger than 0.23%. This is because with the same coolant mass flow ratio, a proportionally larger blockage is created at the smallest tip gap. At the largest tip gap of 2.2% of the chord, the cavity tip achieves the best aerodynamic performance. This is because the effect of the coolant is reduced and the benefits of the cavity tip geometry dominate. At a coolant mass flow ratio of 0.55%, the cooled flat tips produce a lower loss than the cavity tip at tip gaps less than 1.3% of the chord. The cooled cavity tip produces the least loss for tip gaps larger than 1.3% of the chord. The cooled suction side squealer has the worst aerodynamic performance for all tip gaps studied.

Copyright © 2011 by American Society of Mechanical Engineers
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References

Figures

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Figure 1

Tip leakage flow over flat tips (after Denton (1) )

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Figure 3

Mesh of the cooled cavity tip (τ=1.6%C)

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Figure 4

Mixing of tip leakage flow and main flow

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Figure 5

Grid dependency study of a flat tip

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Figure 6

Geometries of the uncooled tips

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Figure 7

Blade surface static pressure distributions

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Figure 8

Flow around uncooled tips (τ=1.6%C), cut plane at 35%Cy

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Figure 9

Tip leakage losses versus tip gap for uncooled tips

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Figure 10

The location of the coolant holes on cooled tips

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Figure 11

Coolant supply method

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Figure 12

Tip leakage loss versus coolant mass flow ratio (τ=1.6%C), experimental results

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Figure 13

Tip leakage loss versus coolant mass flow ratio (τ=1.6%C), CFD

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Figure 14

Predicted static pressure distribution across the flat tips (30.2%Cy)

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Figure 15

Predicted flow path lines of the fourth coolant hole on the Flat_S tip, Mc=0.33%

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Figure 16

Predicted velocity contour maps over the pressure side and suction side of the flat tip (τ=1.6%C)

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Figure 17

Tip leakage mass flow ratio versus coolant mass flow ratio (τ=1.6%C), CFD

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Figure 18

Predicted static pressure distribution across the cavity tips (35%Cy)

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Figure 19

Predicted flow path lines of the seventh coolant hole on the cooled cavity tip, Mc=0.33%

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Figure 20

Predicted velocity contour maps over the pressure side and suction side of the cavity tip (τ=1.6%C)

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Figure 21

Two-dimensional mixing model

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Figure 22

Tip leakage loss versus coolant mass flow ratio (τ=1.6%C), mixing model

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Figure 23

Loss inside the tip gap and blade passage versus coolant mass flow ratio (τ=1.6%C), mixing model

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Figure 24

Tip leakage loss of cooled tips versus coolant mass flow ratio (τ=1%C), Exp.

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Figure 25

Tip leakage loss of cooled tips versus coolant mass flow ratio (τ=2.2%C), Exp.

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Figure 26

Tip leakage loss versus tip gap Mc=0.55%, Exp.

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