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TECHNICAL PAPERS

Effects of Reynolds Number and Freestream Turbulence on Turbine Tip Clearance Flow

[+] Author and Article Information
Takayuki Matsunuma

 National Institute of Advanced Industrial Science and Technology, 1-2-1 Namiki, Tsukuba, Ibaraki 305-8564, Japan

J. Turbomach. 128(1), 166-177 (Feb 01, 2005) (12 pages) doi:10.1115/1.2103091 History: Received October 01, 2004; Revised February 01, 2005

Tip clearance losses represent a major efficiency penalty of turbine blades. This paper describes the effect of tip clearance on the aerodynamic characteristics of an unshrouded axial-flow turbine cascade under very low Reynolds number conditions. The Reynolds number based on the true chord length and exit velocity of the turbine cascade was varied from 4.4×104 to 26.6×104 by changing the velocity of fluid flow. The freestream turbulence intensity was varied between 0.5% and 4.1% by modifying turbulence generation sheet settings. Three-dimensional flow fields at the exit of the turbine cascade were measured both with and without tip clearance using a five-hole pressure probe. Tip leakage flow generated a large high total pressure loss region. Variations in the Reynolds number and freestream turbulence intensity changed the distributions of three-dimensional flow, but had no effect on the mass-averaged tip clearance loss of the turbine cascade.

Copyright © 2006 by American Society of Mechanical Engineers
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References

Figures

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Figure 1

Total pressure loss (zero clearance)

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Figure 2

Annular turbine wind tunnel

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Figure 3

Geometry of turbine cascade

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Figure 4

Design velocity and pressure distributions on surface at turbine cascade midspan

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Figure 5

Measurement locations

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Figure 6

Adjustment of freestream turbulence intensity

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Figure 7

Spanwise distributions of inlet velocity, total pressure loss, and turbulence intensity at three Reynolds numbers (freestream turbulence intensity Tuin=0.5%, axial position z∕Cax=−0.706=−0.706)

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Figure 8

Spanwise distributions of inlet velocity, total pressure loss, and turbulence intensity at three freestream turbulence intensities (Reynolds number Reout=13.4×104, axial position z∕Cax=−0.706=−0.706)

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Figure 9

(Color) Effect of Reynolds number on total pressure loss distributions at exit of turbine cascade (Tuin=0.5%)

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Figure 10

(Color) Effect of freestream turbulence intensity on total pressure loss distributions at exit of turbine cascade (Reout=13.4×104)

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Figure 11

Mass-averaged exit loss

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Figure 12

Measured tip clearance loss

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Figure 13

Measured and predicted tip clearance losses

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Figure 14

Effect of Reynolds number on secondary flow vector distributions at exit of turbine cascade (Tuin=0.5%)

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Figure 15

Effect of Reynolds number on trace of secondary flow (Tuin=0.5%)

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Figure 16

(Color) Effect of Reynolds number on axial vorticity distributions at exit of turbine cascade (Tuin=0.5%): line contours of total pressure loss superimposed on flood contours of axial vorticity

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Figure 17

Effect of freestream turbulence intensity on trace of secondary flow (Reout=13.4×104)

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Figure 18

Effect of Reynolds number on spanwise distributions of flow angle (Tuin=0.5%)

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Figure 19

Mass-averaged exit flow angle

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Figure 20

Decrease in exit flow angle due to tip clearance

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