Impulse Mistuning of Blades and Vanes

Abstract

Impulse mistuning is an alternative approach for the reduction of vibration stresses of blades and vanes. In contrast to most other approaches, it is not a direct energy dissipation approach but a mistuning based one. However, the approach is not aimed at making use of the geometrical mistuning of the structure (e.g., a blade or a vane stage). Mistuners, specially designed small bodies are placed at specific locations inside of the component, e.g., of a blade or of a vane. They do not directly dissipate enough energy to cause relevant damping like a friction or friction-impact damper, because of the small mass involved, but rather mistune the eigen frequencies of the structure using impulses (impacts). As a result, the structure absorbs less energy at the original resonance and hence answers with lower vibration amplitude. In fact, impulse mistuning is a special case of absorption—the so-called targeted energy transfer (TET) with “vibro-impact nonlinear energy sinks” (VI-NES)—with very small impact mass involved, and thus, a negligible role of dissipation while experiencing a significant amount of absorption. The energy will be transferred (or “pumped”) to other resonances, sometimes outside of the primary resonance crossing and partially dissipated. We use the names “impulse mistuning” or “mistuners” instead of TET or VI-NES because (in our opinion) it better describes the physics of this special kind of absorption. In the paper, the design and validation of two impulse mistuning systems, for a blade stage and a vane cluster of a lower power turbine, are presented.