Influence mechanism and quantificational evaluation of key factors affecting flutter stability of a transonic fan

Abstract

The blade flutter stability directly affects the stable operating range of the aero-engine. A few factors related to flutter stability, such as the shock wave, separation flow, inter-blade phase angle (IBPA), and so on, have been found in existing flutter mechanism studies. However, the mechanisms of several factors affecting flutter stability remain to be determined. Taking a transonic fan, NASA rotor 67, as the research object, this paper studies the main factors affecting the blade flutter stability and their influence mechanisms through the unidirectional Fluid-Structure-Interaction (FSI) simulation. The amplitude and phase of unsteady pressure caused by various factors determine the aerodynamic damping distributions of the blade under different operating conditions, which are obtained by the energy method. A quantificational method based on increment proportion is proposed to evaluate the effects of various factors on blade flutter stability by the ratio of the work increment done by each influencing factor to the total work increment, and the flutter stability analysis method is further established. Using this proposed method, it is found that the dominant factors affecting flutter stability before and after design point are inconsistent, which are the shock wave on the suction surface and tip leakage flow, respectively. Furthermore, the mapping relationship of nodal diameter (ND) and flutter stability is also investigated, and the influence mechanism is revealed in this research. The results demonstrate that the nodal diameter affects the amplitude and phase of unsteady pressure by affecting the amplitude and phase of shock wave oscillation, thus affecting the blade flutter stability.