大涵道比涡扇发动机分开式排气系统设计参数影响研究

为了分析外涵可用压比、内外涵出口面积以及核心外罩长度四个参数对大涵道比涡扇发动机分开式排气系统气动性能的影响，以该排气系统为原型采用数值模拟的方法对其性能进行研究。结果表明：存在一个最佳外涵可用压比使推力系数最大，但此时外涵处于欠膨胀状态，其设计规律与单喷管设计不同；存在一个使得推力系数最大的最佳喷管出口面积，此时喷管处于微弱的过膨胀状态，这主要与核心外罩／尾锥上的压强分布有关；核心外罩长度对排气系统性能存在一定程度的影响。

The numerical investigation into the effect of design parameters on high bypass ratio separate flow exhaust system performance

Numerical simulation method of high bypass ratio separate flow exhaust system is adopted and satisfactory result has obtained. Based on the initial exhaust system, the influence of the different outlet area of external and internal bypass, the different length of the outer casing and tail cone on the aerodynamic performance have been investigated. Through analysis and investigation, this paper provides the working foundation to the design of the similar exhaust systems. The results show the existence of an optimal available pressure ratio of external bypass which makes thrust coefficient maximum, but the external bypass will be at under-expanded state when the pressure ratio is adopted. Its design is different from the single channel nozzle. Secondly, there is an optimal outlet area of nozzle which makes thrust coefficient maximum, but the nozzle will be at over-expanded state when the outlet area is adopted. It mainly depends on the pressure distribution of the outer casing and tail cone. Thirdly, the length of outer casing also influences the performance of the exhaust system.