Mistuning Strategy on Long Blades to Mitigate Flutter

Nowadays, the current favoured form for energy production is combined cycle, which allows efficient solutions through reduction of fuel consumption and hence a lower impact in terms of pollutant emissions. At the same time, the continuous request of more efficient solutions translates into large, higher flowing machines with slender and loaded blades. The design of such blades now needs to include aeromechanical interactions, such as transonic conditions at the tip, leading to shock wave systems that impinge on and interact with the blade surfaces and high load conditions increasing the occurrence of flow induced vibrations as flutter. Nowadays reliable CFD prediction models are used to estimate flutter stability based on the minimum of the logarithmic decrement curve to design robust configurations for the long rotor blades. Currently, mistuning is one of the most used flutter mitigation techniques as it can be implemented in the field via, for instance, blade mass removal (e.g. Trailing Edge cutback), that also leads to a performance degradation. Methods are available for the application of mistuning to free standing blades. This paper provides an introduction to the physics of and methodology for determining mistuning solutions on mechanically coupled blade systems.