Master thesis and internship[BR]- Master's thesis : Experimental and numerical analysis of vibrations in variable stator vanes[BR]- Internship

Abstract

In the new high speed booster currently developed at Safran Aero Booster, the use of variable stator vanes seems necessary. This structure is made of several pieces which makes the prediction of vibration frequencies difficult. Indeed, the methodology currently in use at Safran Aero Boosters leads to frequency differences up to 50 % between experimental and numerical results.

This thesis aims at studying the different methodologies and models available at Safran Aero Booster in order to find a method enabling a better estimation of the resonance frequencies than the one currently in use. This study covers different aspects of the correlation procedure from the post-processing of the signal measured during the tests to the introduction of nonlinearities in the model.

The methodology used at Safran Aero Booster is first reviewed to establish its limitations and identify points that could be improved. Then, several sets of post-processing parameters are used to determine the modes relevant for the rest of the study as well as the frequency precision that will be expected from the models.

Afterwards the resonance frequencies obtained in Ansys Mechanical with a vane alone and a complete model are compared. These models are studied in various configurations therefore enabling to determine the importance of the different boundary conditions considered. Since the complete model is more representative of an actual variable stator vane assembly, it is also determined if adding complexity in the model enable to obtain an improved prediction of the frequencies.

Based on the analysis of the boundary conditions and of the pieces that compose the assembly, a model taking into account some nonlinearities is built in Ansys Motion in order to represent the influence of contacts on the resonance frequencies.

This work finally provides a suggested methodology for vibration prediction as well as areas for improvement in the modeling of variable stator vanes.