Effects of tip clearance on non-synchronous aerodynamic excitation of compressor rotor blades

Abstract

Abstract The unstable tip flow of compressor rotor may cause the aeroelastic problems, inducing the non-synchronous vibration with high amplitude level, which has a significant effect on blade high cycle fatigue and safety. In order to investigate the effects of tip clearance on non-synchronous aerodynamic excitation of compressor rotor blades, the full annular numerical simulations were conducted for the unsteady flow field of a 1.5-stage compressor under near stall conditions. The frequency characteristics of non-synchronous aerodynamic excitation and tip unstable flow structure were analysed for different tip clearances (0.5%C, 1.0%C, 2.0%C, and 3.0%C). The results showed that the frequency and amplitude are strongly influenced by the tip clearance size. For 0.5%C tip clearance, the main frequency of non-synchronous aerodynamic excitation is the low-frequency aerodynamic excitation frequency, which is mainly caused by tornado-like vortex in the tip suction side, the dominant aerodynamic disturbance mode number is 19. For 2.0%C and 3.0%C tip clearance, the dominant aerodynamic disturbance mode number is 47, and the main aerodynamic excitation frequency is high frequency non-synchronous aerodynamic excitation frequency, mainly caused by the shedding vortices propagating circumferentially at the blade tip, exhibiting the feature of “rotating instability”.