Application of a Direct Aeroelastic Coupling Method to a Vibrating Transonic Compressor Cascade

Kurzfassung

A new technique is presented in this paper which analyzes the aeroelastic behaviour of an oscillating compressor cascade in the time domain. In contrast to the classical linearized determination of the aeroelastic stability in the frequency domain where the computation of the unsteady aerodynamic forces is uncoupled from the calculation of aeroelastic stability boundaries, the present method simultaneously solves the structural and fluid equations using a specific coupling technique. The computed time series of the aeroelastic simulation of a system of twenty compressor blades performing torsional vibrations are presented. While the structural part of the governing aeroelastic equations is time-integrated by the algorithm of Newmark, the unsteady airloads are computed at every time step by an Euler upwind code. The vibrational behaviour of the cascade was investigated for two different flow cases: a pure subsonic flow and a transonic flow, where in the latter case the nonlinear fluid-structure interaction caused by oscillating shocks may significantly influence the aerodynamic damping of the blades. For the given cascade, of which each blade is modelled as a single-degree-of-freedom system, time dependent blade amplitudes were calculated for tuned as well as for mistuned blade assemblies.