Session: 24-03 Advances in Design & Analyses

Paper Number: 121385

121385 - Multi-Stage Cyclic Symmetry Analysis of an Industrial High Pressure Turbine Assembly – Comparing Structural, Modal, and Solve Statistics 

Structural analysis of rotating turbomachinery geometry typically can take advantage of cyclic symmetry reduction to facilitate faster solve times and reduced result file size requirements.  Historically, these analyses have been limited to decomposing the geometry to a single cyclic sector that shares a common sector count. Concessions are often made in these analyses (eliminating features that don’t share a common sector count, artificially changing airfoil counts to force sector counts that are factors of each other, or modelling multiple sector that share a common factor together in a large segment – i.e. model a 1/3 sector) because the savings in solve time and file size reduction are invaluable versus trying to solve a full 360° representation of the geometry.

Multi-stage cyclic symmetry is a newer theoretical technique to create and analyze geometric models that consist of multiple cyclic sectors that have different sector counts. In this technique, each continuous collection of bodies that share a common sector count is collectively called a “stage”.  Special consideration is needed at the connections between stages to ensure displacement continuity between the cyclic pattern of one stage to the next.

The theory behind this technique assumes that each stage of the model can be represented by a cyclic solution consisting of a combination of Harmonic Indices. A user can specify which Harmonic Indices they want to use for each of the stages (often a single harmonic index is used to start and more can be added to improve the fidelity of the solution). This theory originates from linear dynamics but it also has applications for static structural analyses. By reducing the model to a series of connected cyclic stages, the solve times and result file sizes can be significantly reduced when compared to an accurate full 360° representation.

This technique has been demonstrated on many simpler academic cases and has been shown to provide accurate results for a properly setup analysis model.  The aim of this paper is to use the multi-stage cyclic symmetry approach on a full two stage high pressure turbine assembly (consisting of non-proprietary geometry representative of an industrial assembly) to analyze both a static structural analysis for stress, as well as a modal analysis for natural frequencies and mode shapes. The paper will compare the results from running the same geometry as a full 360° reference case to check the multi-stage analysis for accuracy.  Solve times and result file sizes will also be compared to show the benefits of using the multi-stage cyclic symmetry technique. 

Presenting Author: Jeffrey Bronson ANSYS Inc

Presenting Author Biography: Jeff Bronson obtained his Masters of Science in 2004 from the University of Michigan while studying Aerospace Engineering with a focus on aerospace structures.

After graduating, Jeff moved on to work for a start up company designing and analyzing micro combustion engines before branching out into the aero turbine engine industry. He spent 10 years working for GE Aviation and Williams International where he was on many different functional teams including design, analysis, manufacturing, and project management.

Jeff has built a strong background in mechanical subject areas including coupled thermal/structural analysis of turbine engine systems, creep modeling and engine hot section failure analysis, design optimization, fatigue modeling and testing, linear elastic fracture mechanics (deterministic and probabilistic) and crack growth, material testing for mechanical properties and material model fitting, rotordynamics of turbine engines, and design for manufacturing processes (additive manufacturing, EDM processes, investment casting).

Authors:

Jeffrey Bronson ANSYS Inc