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

为了研究双外涵变循环压缩系统的涵道流动匹配规律，发展了涵道流动的计算模型，对压缩系统模式转换过程中外涵道倒流问题的发生机理和影响因素进行了深入分析，总结了压缩系统的倒流判断准则，并基于简化计算模型和全三维计算结果对倒流判据进行了验证。研究结果表明，对于一定的压缩系统匹配状态，存在一个决定涵道匹配状态的临界核心机驱动风扇级(Core Driven Fan Stage, CDFS)总压比，当CDFS的实际工作压比高于临界压比时，压缩系统第二外涵道将发生倒流，反之则系统不倒流。复杂涵道系统内的流动损失和堵塞等特性对临界CDFS总压比有显著影响，为了准确判断压缩系统的匹配状态，需要对其进行精确模化。基于简化模型得到的压缩系统倒流临界线可以推广至全三维状态，本文提出的倒流判别准则具有较高的可靠性和可行性。

A CFD Model for Bypass Flow in Variable Cycle Engine Compression Systems and Criterion to Predict Flow Recirculation During Mode Transition

To investigate the matching characteristics of bypass flow in the 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.