New Modal Tracking Methods for Cyclic Structures – Application to Centrifugal Compressor Impellers

Abstract This work introduces novel modal tracking techniques for centrifugal compressor impellers, providing a systematic approach to handling the intrinsic complexity of these cyclic structures in dynamic analysis. Vibrational modes in impellers are significantly affected by the hub and shroud, making their design a significant challenge from a dynamic perspective. The interaction of blade and disk modes, especially those involving hub and shroud movements, often leads to potential resonance risks for structural integrity. To mitigate these issues, two innovative methods are presented. The first method tracks vibrational modes across different flow coefficients, revealing the impact of geometric changes on modal behavior. The second method focuses on identifying modal families for a specific impeller geometry over varying Harmonic Indices (HIs), providing insights into critical vibrational patterns. Both methodologies leverage numerical indicators such as the traditional Modal Assurance Criterion (MAC), an energy-based variant (MACe), and other relevant metrics, to efficiently identify and track modes with minimal user intervention. These tools not only streamline the conceptual design phase by predicting potential resonance and forced response issues but also assist engineers in optimizing impellers design. The advancements offered by these tracking techniques allow engineers to better manage the trade-off between aerodynamic performance and structural dynamics, enabling smarter design choices and improved high cycle fatigue (HCF) management from the outset of the design process.