Deformable kinematic modeling of variable stator vane linkage using Ansys Motion Integration internship

Abstract

The pursuit of higher efficiency and reliability in aircraft propulsion has made the compressor a central element in turbofan engine design. Its role is to increase the pressure of the incoming air before combustion, directly affecting engine performance. However, compressors are limited by aerodynamic instabilities such as stall and surge, which can reduce efficiency, generate vibrations, and in severe cases lead to engine failure. Extending the stable operating range of compressors is therefore a key challenge in turbomachinery. A proven way to address this issue is through variable stator vanes. By adjusting the angle of the stator blades according to operating conditions, these systems control the airflow, improve stability margins, and enhance efficiency.

While the aerodynamic function of variable stator vanes is well known, their structural integration requires dedicated studies of the linkage mechanisms that actuate the vanes. This thesis, carried out at Safran Aero Boosters (SAB), focuses on the low-pressure compressor and addresses two main objectives: first, to validate the reliability of Ansys Motion's solver by comparing it with SAMCEF, and second, to prepare the integration of the variable stator vane linkage into a complete stator stage model through static and modal studies.

A preliminary static study on a bending beam evaluated stress computation methods. It showed that the Element Unaveraged formulation in Motion Post matched best with the Elemental Mean output in SAMCEF. Several load cases were then applied to the linkage. The two solvers showed strong agreement, with discrepancies in deformations between 0 and 3 percent and in stresses between 1 and 6 percent, confirming the capability of Ansys Motion for static analyses.

Validation continued with modal analyses. Differences in natural frequencies remained below 2 percent, and the modal assurance criterion showed values between 0.84 and 1 for diagonal terms, indicating a very good correlation. A detailed study highlighted the housing as the dominant component, contributing about 60 percent of both strain and kinetic energy. A 3 millimeter mesh was selected as appropriate, and the housing was reduced with ten modes retained optimally.

To support the integration into the full stator stage, the influence of the outer shroud was assessed. The first three mode shapes of the housing were unaffected by its addition, which is favorable for integration. The shroud was also reduced modally with twenty modes retained, enabling efficient representation of the assembly.