Making Use of Labyrinth Interaction Flow

[+] Author and Article Information
A. Pfau, A. I. Kalfas, R. S. Abhari

Turbomachinery Laboratory, Swiss Federal Institute of Technology, 8092 Zurich, Switzerland

J. Turbomach 129(1), 164-174 (Mar 01, 2004) (11 pages) doi:10.1115/1.2218571 History: Received October 01, 2003; Revised March 01, 2004

It is the aim of this publication to attract the designers attention to the end wall flow interactions of shrouded high pressure turbines. One of the key issues for designing better turbines is the understanding of the flow interactions set up by the presence of labyrinth seals. Those interaction flows are carefully examined in this publication using the control volume analysis and the radial equilibrium of forces acting on streamlines. The consequences on secondary flow development and mixing losses are discussed and quantified. Out of this insight, design recommendations are derived, which attempt to make use of the nature of the labyrinth interaction flow. The open labyrinth cavities are classified in a systematic way. The aim of this approach is to work out the characteristic differences between hub and tip cavities and those having a leakage jet or sucking main flow fluid into the labyrinth. The influence on the main flow is discussed in terms of the incidence flow angle of downstream blade rows and the associated loss production mechanisms. The design strategies presented in this paper follow two paths: (a) Optimization of the mixing losses of the leakage jets at hub and tip is estimated to result in an efficiency increase of up to 0.2%. (b) The nonaxisymmetric shaping of the labyrinth interaction flow path aims at the secondary flow control in downstream blade rows. This approach might contribute in the same magnitude of order as reduction in the mixing losses.

Copyright © 2007 by American Society of Mechanical Engineers
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Figure 1

Meridional cut of the test section

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Figure 2

Pitch-wise mass averaged velocity profiles, cavity 2, Z=0.5: (a) tangential, (b) axial

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Figure 3

Nondimensional static pressure Cps time averaged, rotor relative frame, Z=0.5

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Figure 4

Relative Mach number Mrel, time averaged, rotor relative frame; Z=0.5

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Figure 5

Nondimensional radial velocity component, time averaged, rotor relative frame, Z=0.5

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Figure 6

Time averaged velocity triangles, cavity 2: (a) relative frame, (b) absolute frame

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Figure 7

(a) Rotor relative descriptive flow model, (b)–(d) two-step mixing calculation of leakage and main flow

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Figure 8

Pitch-wise mass-averaged, Z=0.5: (a) total pressure, (b) axial, (c) tangential, (d) radial velocity components

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Figure 9

Pitch-wise mass-averaged velocity triangles, Z=0.5: (a) 0.3% gap, (b) 1% gap

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Figure 10

Downstream stator 2, 1% gap case, Z=0.5: (a) total pressure, (b) radial velocity component

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Figure 11

Flow model for cavity 3

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Figure 12

Radial velocity component, absolute frame: (a) interface surface, R=1, 0.3% gap, (b) Z=0.5, 0.3% and 1% gap

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Figure 13

Relative frame: (a) Radial velocity component, 0.3% gap, R=1, (b) relative stream-wise vorticity, Z=0.83

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Figure 14

Control volume for mass and momentum integration: (a) measurement grid, (b) external forces on control volume Fr, Fz; radius of average streamline curvature

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Figure 15

Rotor relative descriptive flow model and two-step mixing calculation of leakage and main flow

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Figure 16

Nonaxisymmetric shroud design in cavity 2: (a) upstream view of the last sealing gap, (b) side view

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Figure 17

Simple model for shroud design

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Figure 18

Nonaxisymmetric shroud and cavity design, cavity 3: (a) upstream view, Z=0.5, (b) side view with nonaxisymmetric insert

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Figure 19

Shroud leading edge design for reduced rotor passage to cavity flow interaction



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