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Abstract
A time-domain Harmonic Balance method is applied to simulate the blade row interactions and vibrations of state-of-the-art industrial turbomachinery configurations. The present harmonic balance approach is a time-integration scheme that turns a periodic or almost-periodic flow problem into the coupled resolution of several steady computations at different time samples of the period of interest. The coupling is performed by a spectral time-derivative operator that appears as a source term of all the steady problems. These are converged simultaneously making the method parallel in time. In this paper, a non-uniform time sampling is used to improve the robustness and accuracy regardless of the considered frequency set. Blade row interactions are studied within a 3.5-stage high-pressure axial compressor representative of the high-pressure core of modern turbofan engines. Comparisons with reference time-accurate computations show that four frequencies allow a fair match of the compressor performance, with a reduction of the computational time up to a factor 30. Finally, an aeroelastic study is performed for a counter-rotating fan stage, where the rear blade is submitted to a prescribed harmonic vibration along its first torsion mode. The aerodynamic damping is analysed, showing possible flutter.
Acknowledgements
The present Harmonic Balance formulation was developed thanks to the support of the Direction des Programmes Aéronautiques Civils (French Civil Aviation Agency) and of the Aerospace Valley (Midi-Pyrénées and Aquitaine world competitiveness cluster). The authors would also like to thank Snecma from the Safran group for their kind permission to publish this study. Finally, Prof. Li He is gratefully acknowledged for the opportunity to publish in this special issue.