Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE credits
Bladed disk vibrations are recognized to be one of the main challenges in ensuring reliable and safe operation of turbomachinery. The phenomena of low-cycle- and high-cycle-fatigue, caused by flutter and high forced response, are known to be fundamental failure modes of bladed disks. While the first phenomenon is to be avoided at all costs – as it leads to rapid disintegration of the machine, the reduction or suppression of the latter is also desirable, resulting in the overall service cost reduction.
Critical parameter in determining flutter onset is the damping present in the system. The damping can come from energy extraction/insertion from/to the system by the work of fluid flow (aero damping), or from the energy dissipation arising from the nature of material structure or presence of friction surfaces (mechanical damping). While mechanical damping is always positive, aero damping normally drops with rise of flow speed, and can become negative.
Energy insertion to the system can be disrupted effectively by introducing (intentional or not) small geometry/mass variations to the number of blades in the bladed disk - called mistuning. While mistuning can suppress flutter, its side effects can be negative as well. In controlling this phenomenon, damping again plays critical role.
This work deals with analytical predictions of flutter in turbomachinery based on the numerical characterizations of mistuning and mechanical damping. These predictions are based on the utilization of harmonic balance solver for flutter and nonlinear damping problems. The procedures are applied to the FUTURE project LPT blade model. The results obtained are compared to the experimental findings.
2012. , 68 p.