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%.