Relevant Features of Intentional Mistuning in Forced Response Reduction: Application to Centrifugal Impellers

Resumen

Centrifugal impellers are subjected to periodic loads during operation, which can excite modes with localized tip motion, leading to high cycle fatigue and structural failure. Small mistuning, typically caused by wear or manufacturing variations, can significantly amplify the forced response. In this work, we use the Asymptotic Mistuning Model (AMM) to investigate intentional mistuning strategies to reduce this amplification. The AMM assumes that mistuning and damping are small perturbations of the tuned problem, and provides a reduced-order model involving only the active modes contributing to the response. We apply it to a detailed finite element model of an industrial centrifugal impeller, obtaining high accuracy with a drastically simplified system. For this structure, a random mistuning of 0.5% of the sector mass can lead to a 50% increase in response amplitude. The design of an effective intentional mistuning pattern to reduce this amplification is guided by the information of the relevant features in the problem given by the AMM: the modal coupling occurs through particular Fourier coefficients of the sector-to-sector mistuning distribution. With this insight, we show that alternating patterns, effective in bladed-disks, are not suitable here due to the different modal distribution of the impeller. Instead, sinusoidal mistuning patterns targeting the modes present in the response are more effective, reducing both amplification and sensitivity to random mistuning. This is achieved without the need to run costly optimization procedures over an exponentially large number of configurations, as the asymptotic model already identifies the relevant physical mechanisms.