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Research Papers: Gas Turbines: Structures and Dynamics

The Effects of a Parametric Variation of the Rim Seal Geometry on the Interaction Between Hub Leakage and Mainstream Flows in High Pressure Turbines

[+] Author and Article Information
Ivan Popović

e-mail: ivan.popovic@cantab.net

Howard P. Hodson

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

Contributed by the Structures and Dynamics Committee of ASME for publication in the JOURNAL OF ENGINEERING FOR GAS TURBINES AND POWER. Manuscript received December 16, 2012; final manuscript received June 1, 2013; published online September 17, 2013. Editor: David Wisler.

J. Eng. Gas Turbines Power 135(11), 112501 (Sep 17, 2013) (11 pages) Paper No: GTP-12-1486; doi: 10.1115/1.4024867 History: Received December 16, 2012; Revised June 01, 2013

The objective of this work was to assess and understand the effects of a parametric variation performed on a typical overlapping rim seal geometry. The datum geometry has been the focus of a detailed experimental investigation employing a large-scale linear cascade subjected to a range of the mass flow rates and swirl velocities of the leakage air. The parametric variations described in this paper were examined using validated computational fluid dynamics (CFD). As a part of the parametric studies, both the axial and the radial seal clearance between the rotor fin (angel wing) and stator platform were varied as well as the length of the overlap between stator and rotor platforms. In addition, the effects of forward and backward facing annulus steps were also investigated. It has been found that a backward-facing annulus step was detrimental for all conditions considered, while a forward-facing step offered improvements for smaller step heights and/or lower leakage fractions. Tightening of the seal clearances closer to the annulus line improved the sealing effectiveness but often at the expense of increased losses. On the other hand, increasing the overlap length led to improvements in the sealing effectiveness with very small effects on the overall losses. Moving the rim seal away from the blade-leading edges reduced the pressure asymmetry at the rim seal and increased the flow uniformity of the leakage air. However, this led to an increased cross-passage flow (more negative skew) and higher losses at all but lowest leakage fractions. The results presented in this paper highlight the fact that there may not be an optimum rim seal solution that would offer an improvement for the full range of leakage fractions and that, for different rim sealing flows, there may be a different optimum geometry. In addition, rotor disk movements in radial and axial directions at various off-design conditions should be considered as a part of the design process. Based on the presented results, it may be of a benefit to the turbine designer to consider rotor disk designs that would be more biased towards the upstream and outward disk movements, which would result in tightening of the seal clearances and avoidance of a backward-facing annulus step.

Copyright © 2013 by ASME
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References

Figures

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Fig. 1

Computational mesh

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Fig. 3

Rim seal aerothermodynamics in terms of streamlines in meridional plane LF = 1.0%

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Fig. 4

Endwall aerodynamics at LF = 1.0%

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Fig. 5

Flood contours of streamwise vorticity (Cωs) superimposed over line contours of total pressure (CPO) at plane 50% Cx downstream of rotor blades

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Fig. 6

Overall seal performance in terms of aerodynamic losses and sealing effectiveness

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Fig. 7

Leakage-mainstream interaction VCAV,REL = 50% U

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Fig. 8

Predicted effects of axial seal clearance on aerodynamic losses and sealing effectiveness

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Fig. 9

Rim seal aerothermodynamics midpitch meridional plane at LF = 1.0%

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Fig. 10

Effects of overlapping length on aerodynamic losses and sealing effectiveness

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Fig. 11

Effects of radial clearance at nominal flow conditions

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Fig. 12

Rim seal aerothermodynamics at midpitch meridional plane at LF = 1.0% for a variation in radial gap

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Fig. 13

Effects of radial clearance on aerodynamic losses and sealing effectiveness

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Fig. 14

Effects of an upward tooth on aerodynamic losses and sealing effectiveness

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Fig. 15

Cavity pressure versus leakage fraction for an inverse tooth and the datum configuration

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Fig. 16

Effects of annulus steps on aerodynamic losses for a fixed leakage fraction or cavity pressure

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Fig. 17

Incidence angle at inlet plane for various annulus steps

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Fig. 18

Effects of upward tooth on aerodynamic losses and sealing effectiveness

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Fig. 19

Effects of axial seal position on aerodynamic losses and sealing effectiveness

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Fig. 20

Radial velocity normalized by the blade speed at the seal exit plane and limiting streamlines on hub endwall for LF = 1.0%

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Fig. 21

Effects of radial disk movement on aerodynamic losses and sealing effectiveness

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Fig. 22

Effects of axial disk movement on aerodynamic losses and sealing effectiveness

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