An Integrated Numerical Procedure for Flutter and Forced Response Assessment of Turbomachinery Blade-Rows

Nowadays turbomachinery industry aims for more efficient and environmental friendly engines. Following this design trend, turbomachinery blades become lighter and more loaded, thus resulting prone to flutter induced vibrations. It is well known that vibrations can be also induced by aerodynamic forces due to rotor/stator interactions and, when Campbell crossings cannot be avoided, forced response analyses are also required to ensure a safe machine operation. This paper presents an integrated procedure to investigate flutter and forced response and its application to a 1 and 1/2 low pressure transonic compressor stage. The method is based on the open-source FEM solver (CalculiX) and on the in-house CFD code (TRAF). Moreover, a dedicated tool-chain, able to automatically exchange boundary conditions between the two solvers was implemented. For flutter assessment of the rotor, frequencies and mode-shapes are computed with the FEM code and imposed to the CFD flutter analyses (URANS computations with moving blades). At the same time, an unsteady CFD analysis is carried out to evaluate the aerodynamic excitations on the rotor due to up/downstream stators. The different pressure harmonics on the rotor surface, extracted by a run-time DFT algorithm, are used as external loads for forced response analyses. The aerodynamic damping obtained by flutter computations is also included in these dynamic analyses. Finally, the numerical results are compared with experimental data acquired in the context of the EU FUTURE project. Such comparisons confirm the applicability of the above-mentioned procedure in the blade-row design loop.