Experimental and numerical investigations of a scramjet nozzle at various operations

The present paper focuses on the study of a scramjet asymmetric nozzle at various operations by applying both experimental and numerical methods, which confirms the reliability of the single expansion ramp nozzle (SERN) design method under geometric constraints based on maximum thrust theory as well. The pitot pressure measurement is used to calibrate the exit Mach number of the facility nozzle. The combination of schlieren photograph, static pressure measurement and strain-gauge balance is employed to obtain the flowfield feature, pressure distribution along the SERN wall and forces acting on the experimental model. Besides, the numerical method is also applied to achieve the more detailed flowfield and performance of the SERN. The results show that the flowfield structure is obviously different between at the experimental conditions and at the actual flight operations. As the interaction of the nozzle plume with the external flow, the shock waves following the expansion waves at the trailing edge of the SERN are all presented at both overexpanded and underexpanded conditions; however, the SERN core flow is independent of the external flow. The existing of two platforms with high-pressure at the front areas of the ramp and cowl are beneficial for improving the thrust performance, verifying the superiority of the new SERN design method. The error of the force between the numerical and experimental results is relatively small, denoting the capability of the numerical method. Furthermore, along with the increase in the flight Mach number, the axial thrust coefficient is decreased, while the lift and pitching moment coefficients are increased. Compared with the cases at the overexpanded operations, the axial thrust loss arising from the underexpanded flow is more serious at certain operations.