Numerical simulations of flutter mechanism for high-speed wide-chord transonic fan

Abstract

Flutter is a self-excited aeroelastic instability phenomenon that can cause blade failure and lead to safety accidents. This paper investigates the first bending mode flutter behavior of a high-speed wide-chord transonic fan under different operating conditions. The aim is to reveal the relationship between the flow structure and blade flutter stability at different inter-blade phase angles (IBPA). Two methods are used to model the traveling wave propagation along the circumferential direction: the influence coefficient method (ICM) and the traveling wave method (TWM). The former is used to calculate the aerodynamic damping at different IBPA with fewer computational resources, and the latter is used to analyze the relationship between the flow and flutter stability. The results suggest that the most unstable behaviors occur with two nodal diameters (ND) at three representative conditions: near stall, peak efficiency, and choke. The aerodynamic damping distribution of the blade surface is concentrated primarily at the shock wave, separation, and large vibration amplitude regions, whose effects on the blade flutter stability are greatly impacted by the IBPA. When the blade IBPA is small and positive, the shock and separation areas in the suction side reduce the blade flutter stability. This shows that the IBPA strongly affects the unsteady pressure fluctuations, including the direction and shape of the pressure wave propagation, and whether the unsteady pressure can propagate downstream (cut-on) and result in different aerodynamic damping distributions on the blade surface.