Numerical Investigation of the Aerodynamic and Infrared Radiation Characteristics of Spherical Convergent Flap Nozzles

A number of numerical predictions are performed to evaluate the aerodynamic and infrared radiation characteristics of spherical convergent flap nozzles (SCFN). The accuracy of the computations was verified by comparing the calculated wall pressure values to experimentally measured ones. The prediction results show that the vortices produced by the secondary flow at the corner of the divergent section are the main factor to produce thrust loss without any vectoring action. Compared to the axisymmetric nozzle, the SCFN caused up to 1.86% thrust loss and 3% flow rate loss. The yaw angle had no effect on the inner flow field in the divergent section and the exhaust flow because the yaw vector turning is achieved by gimballed subsonic flow. The maximum thrust losses were only 1 and 0.69%, which were caused by the pitch and yaw vector, respectively. The aerodynamic vector angle was approximately consistent with the turning angle due to geometric deflection of SCFN. With a 15° geometric pitch angle, the maximum radiation was depressed by 8.76% on the vertical plane and by 23.9% on the horizontal plane relative to that without pitch. With a 10° geometric yaw angle, the maximum radiation was depressed by 11.8 and 5.7 on the horizontal and vertical planes, respectively.