Investigations on the unsteady flow mechanism of the high-throughflow fan with partial-height booster rotor

Abstract

This paper describes the use of numerical simulations to evaluate the complicated steady and unsteady flow in a high-throughflow fan stage. A detailed investigation of the aerodynamic performance is carried out at the choking point, near-choking point, peak efficiency point, and near-stall point. The peak efficiency point is selected as a typical operating point to clarify the unsteady flow mechanism inside the fan stage. The unsteady simulation results show that the mass flow is lower under all operating conditions than in steady flow, and the difference increases as the operation point approaches the near-stall point. The isentropic efficiency decreases by 0.41% at the near-stall point, but improves slightly at the other points considered. The total pressure ratio does not change significantly. The total pressure loss coefficient of the stator increases significantly, but the changes in the isentropic efficiency of the fan stage mean that the stator has only a slight effect on the performance of the overall stage. An in-depth analysis of the peak efficiency point is conducted. First, the distribution of entropy along spanwise at the outlet of the rotor and stator domain is examined, and the unsteady effects are found to be mainly concentrated near the hub, mid-span, and higher-span of the stator. Detailed analysis of these three regions shows that the main influence comes from the distortion of the transmission of flow field information in the hub boundary layer at the rotor/stator interface, the interaction between the tip vortex and other vortexes near the mid-span region, and the interaction between the trailing edge separation vortex of the fan rotor and the surfaces of the stator.