The energy method is used as the standard method for analysing the flutter behaviour (aeroelastic stability) of compressor rotors and stators. This requires high mass parameters, which are only well known for previously studied metal full blades. The energy method is not a complete flow/structure coupled method, as the natural vibrations of the blading are calculated from a purely structural dynamic eigenvalue analysis (FEM) and fed into the unsteady flow calculations (CFD). As such, the rotation and part of the stationary aerodynamics are considered but without taking into account the reactions of the unsteady aerodynamics. From the unsteady air forces and the oscillating movement, the aerodynamic damping for a sufficiently large number of eigenmodes can be determined (a sufficient number of operating points, three to five blade eigenforms, all phase difference angles) through the exchange of forces between fluid and structure. This procedure, depicted in the figure above, has also been used at the Institute as a standard procedure with the Patran/NASTRAN (occasionally CalculiX) and linearTRACE programs to verify the flutter resistance of test rotors.
The purpose of the EU FUTURE project was, among other things, to compare the methods used in particular cases with one another. The results revealed a high dependency of the results on the quality of the modelling as well as a need to harmonise the parameter definitions in the individual software modules, as well as for general process optimisation. The Institute of Aeroelasticity is therefore planning to expand the calculation steps with defined transfer routines into a robust process chain, which also takes into account the different parameter definitions.