This paper describes the impact of structural deformations on interstage cavity flow dynamics by adopting thermal fluid-structure interaction methods. These coupled numerical approaches solve the fluid-solid heat transfer in conjunction with the geometrical deformation due to mismatched centrifugal and thermal expansion of rotating and stationary turbine discs. Especially the changing clearances at the interstage labyrinth seal, at the rotor blade tips and at the rotor stator rim seals can be captured to calculate the correct flow physics at these locations. A manual explicit coupling approach in ANSYS is utilized that couples the CFX CHT solver with the FE solver Mechanical. The validation of a 3D sector model with experimental data shows improvements in predicting the metal temperature of the rotating walls but also disclose problems with the overheated stationary parts, mainly due to the utilization of steady state mixing planes. Additionally, a surrogate 2D model of the 3D model is introduced to compare the explicit coupling approach with an implicit approach exploiting the ANSYS MFX interface between the fluid and the solid domain. Thereby, the manual coupling approach reveals to be much more efficient for the examined thermal fluid-structure interaction.

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