Design and analysis of the scramjet nozzle with contact discontinuity

Abstract

A scramjet nozzle design method that utilizes Rao's maximum thrust theory and the slip-line unit process is proposed to reduce the negative effect of the internal contact discontinuity on the aerodynamic performance. The proposed method divides the nozzle flowfield into a lower region and an upper region. The compatibility between the two regions with different aerothermal properties is achieved by the constraints of the flow deflection angles and the static pressure along an inviscid slip line. Due to the high computational expense allied with finite rate reactions, particularly for heavy hydrocarbon fuels, the basic studies of scramjet nozzles in this paper are conducted with the chemically frozen flow assumption. It underestimates the influence of the dissociated species of combustion product or unburned fuels to some extent, but still reveals nozzle performance trends efficiently, and serves as a helpful reference. The initial expansion arc radius influences the evolution of the inviscid slip line, thereby changing the expansion processes of the upper and lower regions. However, the position deviation between the nozzle entrance and the exit cannot change the shape of the inviscid slip line except retreating of the terminal point. Notably, a critical position deviation maximizes the axial thrust coefficient and minimizes the lift. Compared with the nozzle designed by the truncated method, the nozzle designed by the proposed method shows increases in the axial thrust coefficient, lift, and pitching moment of 6.22%, 166.3%, and 164.8%, respectively, at the design point. Numerical results also show that only a minor decrease in the nozzle performance appears when 3D effects are considered, further revealing the reliability of the proposed method.