Aeroelasticity and flutter prediction

The main activity related to aeroelasticity is  dedicated to the compressor blades flutter phenomenon, using very efficient unsteady flow methods such as the harmonic balance approach.

With the trend to reduce weight and increase stage loading of aeroengine components, flutter predictions have become a crucial part of turbomachinery design. A practical approach is to compute unsteady aerodynamic loads under forced deformation of the blades at prescribed inter-blade phase angles (that is to say, blades do not vibrate in phase). The basic principle of harmonic methods for time-periodic problems is to Fourier decompose the flow variables. The Time Spectral Method (TSM) used at CERFACS solves the problem in the time domain thanks to the use of inverse Fourier transform. The unsteady problem is thus finally transformed to a set of steady problems coupled by a source term, corresponding to a uniform sampling of the period.

With the developement of specific phase-lag boundary conditions in the TSM framework, computations of compressor blades forced deformation have been performed at CERFACS. A very good accuracy of the flow response has been obtained, as compared to classical nonlinear unsteady simulations. The computationnal saving is about one or two orders of magnitude, depending on the inter-blade phase angle considered.

Contacts: Guillaume Dufour, Frederic Sicot