The aerodynamic characteristics of axisymmetric convergent-divergent nozzle and vehicle afterbody were studied. Based on the response surface method of orthogonal polynomials by combining with the self-programming

the three-dimensional flow field was numerically simulated. Flux coefficient and thrust coefficient were selected as the optimization indicators

while half convergence angle

throat radius

half expansion angle

bottom area and tail contraction angle were selected as the research objects to analyse under two conditions. By constructing and solving the function of response surface

the results show that half convergence angle and half expansion angle affect about 90% of aerodynamic characteristics; half convergence angle

throat radius and bottom area affect about 85% when discussing flux coefficient only; half expansion angle affect about 85% when discussing thrust coefficient only; half convergence angle

half expansion angle and throat radius affect more than 90% when discussing condition H=0km

Ma=0 only; half convergence angle and half expansion angle affect more than 85% when discussing condition H=20km

Ma=2 only.