On the Mechanism of Unsteady Tip Flow Occurrence in a Transonic Fan

Abstract

Abstract. The tip clearance flow, closely related to stable margin and efficiency, influences the performance of the fan/compressor in aeroengines. The unsteady tip flow in a high-speed transonic fan rotor is studied by numerical methods. This phenomenon is considered to be related to the flow instability. This article studied the occurrence and the development of the unsteady tip flow. The unsteady flow structure and the dynamic mode of pressure fluctuation are also demonstrated. The Richardson number in a turbomachinery environment, Riturbo number, is novelly proposed to study the probability of Kelvin–Helmholtz instability inducing the unsteady tip flow. It is found that after the fluctuation occurs, as the flowrate decreases, the Riturbo number shows a downward trend of a power function. When the stability provided by the centrifugal force gradually decreases, the tangential inertia force plays a major role, and the internal instability of the shear layer is prone to occur under the large disturbance caused by the vortex wave interference.