轴对称分开排气喷管改混合排气喷管设计方法

为将涡扇发动机轴对称分开排气喷管改型设计为混合排气喷管以获取混合推力增益且改变其红外辐射(IR)特征，提出了一套基于CFD数值计算评估的轴对称分开排气喷管改型设计方法。研究结果包括:①提出了内、外涵气流不同程度掺混时推力的估算方法，估算值与真实值的误差在所研究参数范围内不超过0.005；②分析了内、外涵气流掺混对改型设计的影响，喷管外涵气流与内涵气流的总压比在0.8~1.5之间且掺混度大于0.1时混合排气最有可能产生推力增益，且掺混越好，增益越高；③轴对称分开排气喷管改型设计为带环形混合器的混合排气喷管后，推力系数增加0.0087~0.0126，而采用波瓣混合器时喷管的推力系数则增加0.0289；④相比于分开排气，混合排气喷管在0°~15°方向上的红外辐射强度有所增加，但在其他所有方位角上均大幅下降，最大降幅为77.5%。 

Modified verison design method of axisymmetric unmixed-flow nozzle to mixed-flow nozzle

In order to achieve the increased gross thrust and different spatial distributions of infrared radiation (IR) characteristics, a modified version design method of axisymmetric unmixed-flow nozzle based on CFD numerical simulation was established to change it into mixed-flow nozzle. Results indicated that: (1) An estimating method of nozzle thrust was proposed when the core and fan flow were mixed at various degrees, the error between the estimated value and the true one was basically less than 0.005 in the parameter scope. (2) Influence on modified version design of the core and fan flow condition was analyzed, increased thrust may be achieved when the total-pressure ratio of fan flow to core flow was between 0.8 and 1.5, and the mixing degree should be larger than 0.1. (3) Increased gross thrust was achieved after the modified version design, the thrust coefficient of mixed-flow nozzles with confluent mixer increased by 0.0087-0.0126 in comparison with the unmixed-flow nozzle; when lobed mixer was adopted, the thrust coefficient increased by 0.0289. (4) The integral IR intensity of mixed-flow nozzle increased in the azimuth angles of 0°-15°, but it significantly decreased in all the other azimuth angles, the largest decline was 77.5%.