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.

Computational and experimental analysis of the impact of a sphere on a beam and the resulting modal energy distribution

“…With the described working principle, the IES does not require dissipation in the contact region. Consequently, the IES and its casing can be designed to avoid the concentration of plastic behavior in the contact region (inevitably associated with damage and thus reducing its service life), which is believed to be crucial from an engineering perspective [6].…”

Vibration Reduction of Mistuned Bladed Disks Via Piezoelectric-Based Resonance Frequency Detuning

“…In a separate approach, Hartung et al utilized small masses located within blade cavities to function as "impulse mistuners." [23] As these impulse mistuners are small, they do not dissipate much energy through sliding friction or from impacts with the sides of the cavity. Instead, the working principle of this concept is that when operating at certain frequencies, the impacts effectively alter the blade's stiffness and, consequently, the blade's natural frequencies, thus avoiding a strong resonant condition.…”

Investigations on amplitude adaptive sequential friction‐spring dampers

“…Impact dampers for example rely on collision masses and have been studied in [3–7] mainly in three variations: with clearance, with a singular impact mass, and with multiple impact masses. Impact dampers were also investigated for turbomaschinery in [8]. Closely related to impact dampers are tuned liquid dampers,9–11 which take advantage of a water tank and sloshing to reduce the main systems amplitudes.…”