Abstract: A numerical investigation was carried out on a high bypass ratio fan booster of a civil-aircraft engine at different rotating speeds under core working conditions. The influence of core working conditions on the bypass characteristics was summarized. Results showed that the bypass surge margin and near-choke mass flow of the fan are reduced as the core condition goes to the near surge point. During the process of obtaining bypass characteristics, the change rule of core aerodynamic performance was grasped as follows:the mass flow, pressure ratio and efficiency of the core get increased as the bypass condition goes to the near surge point, and the core mass flow grows more as the rotating speed is higher. Furthermore, during the process of obtaining bypass characteristics, the twin-duct matching mechanism was clarified, which is essentially determined by the fan characteristic of total pressure ratio and mass flow, as well as the redistribution of mass flow between the core and bypass.

Key words: civil-aircraft engine, high bypass ratio, fan booster, twin-duct matching mechanism, mass flow redistributionhttp