2D Elementary Geometric Decomposition to Study Flutter Motion of a Space Turbine Blisk

Within the framework of aerospace turbines, an isolated integral bladed disk is examined. The blisk presents very high eigenfrequencies with complex deformations of the blades. A 3D steady RANS computation is at first performed with the aim of characterizing the subsonic flow. Then a simplified 2D approach is considered in order to study fluid-structure interaction and to evaluate the stability: the blades have been found stable. In addition, an original method to better understand the level of stability is presented: the blade vibration is decomposed into elementary geometric movements in order to dissociate the different mechanisms that participate to reach stability. With the assumption of first-order behaviors, the linearized RANS unsteady fields corresponding to both the full deformation and the elementary movements are calculated. Some elementary relative blade movements appear to be either stabilizing or destabilizing when looking at the aerodynamic damping coefficient. The coupling between these elementary movements has also been investigated. Either constructive or destructive interference have been observed. The conclusions that emerge from this study are in line with the results of the classical bending-torsion flutter theory and lead to the improvement of the structure in terms of stability by modifying its mode shape.