Experimental and computational investigation of a over-expanded single-expansion-ramp-nozzle

An experimental study was conducted at low nozzle pressure ratios (NPRs) between 4-10 to determine the wall static pressure distributions of a high-speed 2-D single-expansion-ramp-nozzle (SERN) under wind-off condition. The jet exhaust was simulated with high-pressure air. A computational investigation was conducted to determine the performance of the nozzle and enrich the information of flowfield. The results indicate that under the highly overexpanded conditions, the inner plume shock wave, the boundary layer separation shock wave, free shock separation (FSS), shock-induced separation (SIS), the cross and the interaction of two aforementioned shock waves could be identified and discerned clearly. The axial thrust coefficient C_fa is as low as 0.78-0.87 due to low pressures acting on the expansion ramp surface. In addition, the thrust vector angle δ_p is up to 18°-25°, which must be overcome by shifting the vehicle center-of-gravity or by using the vehicle control surface.