核心机驱动风扇级气动参数径向分布对变循环发动机性能的影响*

The effect of radial distribution of core driven fan stage aerodynamic parameters on variable cycle engine performance

关键词:  变循环发动机  核心机驱动风扇级  多维度仿真模型  迭代耦合方法  气动参数径向分布

Key words:  variable cycle engine  core driven fan stage  multi-level model  iterative coupled approach, radial distribution of aerodynamic parameter

摘要:

为了考虑部件流动细节对发动机性能的影响,本文采用迭代耦合方法建立了变循环发动机(Variable Cycle Engine,VCE)多维度仿真模型。在VCE多维仿真模型中,核心机驱动风扇级(Core Driven Fan Stage, CDFS)三维仿真模型的结果以流量修正因子、压比修正因子和等熵效率修正因子的形式反馈给VCE零维仿真模型,对CDFS的特性图进行修正。在考虑CDFS气动参数径向分布的影响时,需要根据CDFS涵道比及三维仿真结果计算CDFS内、外涵的流量、压比及等熵效率,并以修正因子的形式反馈给VCE零维仿真模型。同时,VCE零维仿真模型需要以CDFS外涵特性图的辅助变量β值取代CDFS涵道比作为迭代变量。结果表明：在不同的VIGV角度下,CDFS外涵区域的等熵效率均低于内涵区域的等熵效率；在VIGV角度为15°时,外涵区域的压比低于内涵区域的压比,而在VIGV角度为40°时,叶尖区域的流动分离更为严重,导致转子进口的攻角增大,转子叶尖区域的负荷加重,外涵区域的压比高于内涵区域的压比；CDFS气动参数径向分布对VCE性能有较为明显的影响,CDFS内涵压比的升高及外涵压比的降低导致发动机核心流流量的增加及总增压比的升高,进而引起发动机推力的增加,推力最大变化为1.75%。

Abstract:

In order to take into account the effect of details of flow field on the engine performance, the iterative coupled approach is applied to establish the multi-level model for variable cycle engine (VCE). In the VCE multi-level model, the three-dimensional simulation result of the core driven fan stage (CDFS) is fed back to the VCE zero-dimensional simulation model in the form of correction factors of mass flow rate, pressure ratio and isentropic efficiency. All the three correction factors are used to modify the default map of CDFS. When the effect of radial distribution of CDFS aerodynamic parameters is under consideration, the mass flow rate, pressure ratio and isentropic efficiency of CDFS core and bypass flow are calculated respectively according to CDFS bypass ratio and the result of three-dimensional simulation. All these parameters are fed back to VCE zero-dimensional simulation model in the form of correction factors. Meanwhile, CDFS bypass ratio is replaced by auxiliary variable β as an iterative variable in the zero-dimensional simulation model. The results indicate that the isentropic efficiency of the bypass zone is lower than that of core zone under variable VIGV angles. The pressure ratio of bypass zone is lower than that of core zone when VIGV angle is 15°. However, the flow separation near the blade tip of VIGV is severer than middle and hub zone what leads to the increase of incidence angle for the rotor blade tip. It means that the workload of the rotor blade tip increases and the pressure ratio of bypass zone are higher than that of core zone. And the radial distribution of CDFS aerodynamic parameters has a significant effect on the VCE performance. The increase in pressure ratio of core flow and the decrease in pressure ratio of bypass flow contribute to the increase of mass flow rate and total pressure ratio of core engine, and it causes the increase of engine thrust finally. The maximum change in engine thrust is 1.75 percent.