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Research Papers

Thermo-Mechanical Finite Element Analysis/Computational Fluid Dynamics Coupling of an Interstage Seal Cavity Using Torsional Spring Analogy

[+] Author and Article Information
Dario Amirante1

Nicholas J. Hills

Thermo-Fluid Systems UTC,  University of Surrey, Guildford, Surrey, GU2 7XH, UKn.hills@surrey.ac.uk

Christopher J. Barnes

Rolls-Royce plc, Derby, DE24 8BJ, UKchristopher.barnes@rolls-royce.com

1

Corresponding author.

J. Turbomach 134(5), 051015 (May 11, 2012) (9 pages) doi:10.1115/1.4004259 History: Received February 08, 2011; Revised March 05, 2011; Published May 10, 2012; Online May 11, 2012

The optimization of heat transfer between fluid and metal plays a crucial role in gas turbine design. An accurate prediction of temperature for each metal component can help to minimize the coolant flow requirement, with a direct reduction of the corresponding loss in the thermodynamic cycle. Traditionally, in industry fluid and solid simulations are conducted separately. The prediction of metal stresses and temperatures, generally based on finite element analysis, requires the definition of a thermal model whose reliability is largely dependent on the validity of the boundary conditions prescribed on the solid surface. These boundary conditions are obtained from empirical correlations expressing local conditions as a function of working parameters of the entire system, with validation being supplied by engine testing. However, recent studies have demonstrated the benefits of employing coupling techniques, whereby computational fluid dynamics (CFD) is used to predict the heat flux from the air to the metal, and this is coupled to the thermal analysis predicting metal temperatures. This paper describes an extension of this coupling process, accounting for the thermo-mechanical distortion of the metal through the engine cycle. Two distinct codes, a finite element analysis (FEA) solver for thermo-mechanical analysis and a finite volume solver for CFD, are iteratively coupled to produce temperatures and deformations of the solid part through an engine cycle. At each time step, the CFD mesh is automatically adapted to the FEA prediction of the metal position using efficient spring analogy methods, ensuring the continuity of the coupled process. As an example of this methodology, the cavity flow in a turbine stator well is investigated. In this test case, there is a strong link between the thermo-mechanical distortion, governing the labyrinth seal clearance, and the amount of flow through the stator well, which determines the resulting heat transfer in the stator well. This feedback loop can only be resolved by including the thermo-mechanical distortion within the coupling process.

FIGURES IN THIS ARTICLE
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Copyright © 2012 by American Society of Mechanical Engineers
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Figures

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Figure 1

Schematic representation of the coupling process

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Figure 2

Torsional springs for two adjacent triangles

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Figure 3

Geometry of the turbine. Enclosed in the square is the stator well where the coupling takes place

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Figure 4

Fluid domain extracted from the finite element model

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Figure 5

Cycle definition expressed in terms of the rotor angular velocity

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Figure 6

Thermal coupling. Meridional streamlines superposed on contours of the swirl number. (a) Low power regime. (b) High power regime

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Figure 7

Thermo-mechanical coupling. Temporal evolution of axial (a) and radial (b) displacement of two opposite points located in the labyrinth and belonging to rotor cavity (solid line) and stator disk (dashed line).

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Figure 8

Thermo-mechanical coupling. Deformed CFD domain at time t = 676 s (HP). Red lines identify the undeflected shape. (a) Overall view. (b) Close-up view of the labyrinth.

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Figure 9

Mesh adaptation by spring analogy. Close-up view of the labyrinth region. (a) Undeformed mesh at time t = 0 s. (b) Mesh at time t = 676 s (HP).

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Figure 10

Mesh adaptation by spring analogy. Close-up view of the rim seal region. (a) Undeformed mesh at time t = 0 s. (b) Mesh at time t = 676 s (HP).

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Figure 11

Mesh adaptation by spring analogy with disabled “sliding” option. Close-up view of the labyrinth region at time t = 676 s (HP).

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Figure 12

Thermo-mechanical coupling. Meridional streamlines superposed on contours of the swirl number. (a) and (c) Low power regime. (b) and (d) High power regime.

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Figure 13

Temperature histories at the three monitoring points located as in Fig. 8. In the legend, OT refers to thermal coupling and TM to thermo-mechanical coupling

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