变循环压缩系统涵道流动计算模型及模式转换倒流判据研究

To investigate the matching characteristics of bypass flow in the variable cycle engine double-bypass compression system, a bypass model is developed, and the mechanism of outer bypass flow recirculation during mode transition is discussed thoroughly. Based on the discussion, a criterion which could be used to judge the system matching state is proposed. The criterion is then tested using results from the simplified model and the full three-dimensional models. Results show that for each state of a given compression system, there exists a critical core driven fan stage (CDFS) total pressure ratio that decides the bypass matching pattern. Exceeding the critical total pressure ratio will incur outer bypass recirculation while keeping the CDFS operation point under the critical value helps to avoid it. It is also found that the flow loss and blockages in the complex bypass system have significant influences on the critical CDFS total pressure ratio, hence need to be modeled accurately when judging the system matching state. The critical boundary acquired from the simplified model can be extended to the full three-dimensional model, thus validating the reliability and feasibility of the judging criterion.