Fan Flutter Mechanisms Related to Blade Mode Shape and Acoustic Properties

Abstract

The blade mode shape and acoustic properties are important factors that affect the aeroelasticity of fan blades. The goal of this paper is to investigate the stall flutter mechanism associated with the first mode and its components. The paper numerically studies the impact of blade modes on fan flutter under different acoustic propagation conditions. The research focus includes unsteady characteristics inside blade passages, variations in pressure waves under different acoustic modes, as well as the effects of blade modes on the least stable phase angle. The results show that the twist-induced pressure leads to destabilization. Compared with the work of other authors, this study discovered that when the twist-induced pressure on the pressure side act on the plunge rather than twist, the instability effect will be greater, while the effect of twist-induced pressure on suction side is weak. The phase of unsteady pressure in two-dimensional flow regions is linear with frequency, while the amplitude is highly sensitive to acoustic properties. The plunge-induced pressure inside the passage undergoes significant changes when downstream is from acoustic cut-off to cut-on. The twist-induced pressure is more sensitive to changes in the acoustic propagation state, with the peak of the aerodynamic damping curve near upstream acoustic resonance being solely related to the twist-induced pressure acting on the suction side. The study also finds that the position of the blade torsion axis, represented by the twist-to-plunge ratio, does not affect the most unstable nodal diameter.