A new design method of single expansion ramp nozzles under geometric constraints for scramjets

A new method based on maximum thrust theory to design a two-dimensional single expansion ramp nozzle with geometric constraints directly is presented in this paper. To generate the contour of the nozzle, the inviscid flowfield is calculated by using the method of characteristics and the reference temperature method is applied to correct the boundary layer thickness. The computational fluid dynamics approach is employed to obtain the aerodynamic performance of the nozzles. The results show that the initial arc radius slightly influences the axial thrust coefficient and that the variations in the length and initial expansion angle of the cowl significantly affect the axial thrust coefficient. The nozzle designed by truncating ideal nozzle is also investigated for comparison to verify the superiority of this new method. The nozzle designed by this proposed method shows increases in the axial thrust coefficient, lift, and pitching moment of 5.5%, 1098.2% and 20.3%, respectively, at the design point. Moreover, the proposed nozzle provided the positive lift with considerable increments in the axial thrust coefficient and in the pitching moment at off-design operations.