Sensitivity Analysis With Respect to Flutter-Free Design of Compressor Blades

In this paper, the rotor geometries of two consecutive design loops are compared numerically with respect to aeroelastic stability. Therefore, the TRACE code of the German Aerospace Center DLR is used to compute the flutter predictions: based on a three-dimensional steady solution, the time-linearized Navier-Stokes equations are solved in order to assess the aerodynamic damping so that the critical inter-blade phase angles can be determined. Apart from the global stability behaviour the computation of local excitation per surface area is presented, facilitating the identification of stabilizing and destabilizing effects due to blade motion and flow field disturbances. Aiming for flutter-free design of compressor blades, an exemplary sensitivity analysis on the first mode is performed. Within the scope of this study, reduced frequency and mass ratio are varied and the influence of these parameters on the stability behaviour is deduced. For a tuned system, the nondimensional flutter equations are derived introducing the flutter index as aeroelastic similarity parameter. Differing tendencies of the aerodynamic work entry and the corresponding logarithmic decrement concerning flutter susceptibility are discussed in detail.