Numerical Investigation of Transonic Stall Flutter Mechanisms of a NACA3506 Rotor

Kurzfassung

A numerical flutter stability study of a two-dimensional compressor cascade with a NACA3506 profile was performed using a one-way prescribed-motion approach. Flutter onset was determined using the Energy Method. The Favre-averaged Navier-Stokes equations were solved using frequency domain methods. Unsteady simulations over the entire working range of the compressor were performed using a linear solver to create a flutter stability map and evaluate overall flutter stability limits. Operating points in a transonic flow regime near stall were selected, to investigate the physical mechanisms causing flutter onset in this flow regime for the first bending and first torsion mode. This analysis was performed using a nonlinear Harmonic Balance solver. The shock on the suction side near the leading edge and its interaction with the boundary layer was identified as a key mechanism causing transonic stall flutter in both the bending and torsion mode. For all operating points investigated in the present configuration, near-stall flutter onset was associated with shock-induced separation and reattachment. The shock leads to an increased phase shift in aerodynamic work. For operating conditions with strong shocks, this leads to a local excitation of the oscillation compared to the damping behavior near the working line. Further downstream for these operating conditions, the phase of aerodynamic work has a strong destabilizing behavior, but no direct cause was found.