The Effect of Tip Clearance on Fan Aeroelasticity Considering Acoustic Propagation Characteristics

Abstract

Tip clearance is a critical parameter affecting fan performance and aeroelastic stability. This paper investigates the effect of tip clearance on fan aeroelasticity under different acoustic propagation characteristics through numerical simulations. Focusing on the first bending mode, which is most prone to flutter, the aeroelastic stability under various nodal diameters (ND) is studied using the energy method, with a detailed analysis of the 2 ND mode, which exhibits flutter risk. The study reveals that tip clearance does not alter the position of the most unstable nodal diameter. Under upstream and downstream cutoff mode and upstream cut-on mode, increasing tip clearance enhances aerodynamic damping, whereas under downstream cut-on mode, it reduces aerodynamic damping. The aerodynamic damping of the blade is jointly influenced by the flow field and acoustic propagation characteristics. The impact of the flow field is primarily concentrated near the leading edge of the pressure side at the blade tip, while the acoustic propagation characteristics significantly alter the phase of unsteady pressure, leading to notable changes in energy exchange characteristics. The study concludes that there is no optimal aeroelastic clearance, as the effect of clearance on aeroelasticity is closely related to acoustic propagation characteristics.