To investigate how the parabolic nozzle flow separation process is affected by three contour parameters

namely initial expansion curve radius

inlet angle and exit angle

the flow field parameters under different contour parameter combinations were numerically simulated

the changing processes of the nozzle flow separation position and separation mode with the increases of gas chamber pressure were obtained. The flow separation mode variation process with chamber pressure was gained. Results show that these three parameters can influence the development of nozzle flow field during engine starting

the flow separation mode transition nozzle pressure ratio(NPR) keeps a positive relationship with the initial expansion curve radius within a certain range. Restricted shock separation can be put off and shortened by suitable design of inlet angle and exit angle. The conclusion provides a possible way to solve the side load problem.