An experimental study was conducted for two high-speed two-dimensional(2-D) single-expansion-ramp-nozzles with different ramp contours at nozzle pressure ratios Rnp between 4 and 60 under wind off condition.The wall static pressure distributions and schlieren flow visualization were obtained.A computational investigation was also conducted to determine the performance of the nozzle and enrich the details of flowfield.Results from this study indicate that under highly overexpanded conditions of cowl trailing edge

the inner nozzle flow is dominated by shock-induced boundary-layer separation and accompanied by four to five oblique shocks.Moreover

the free shock and restricted shock separation are identified respectively in SERN 1 and SERN 2

which exert large influence on the wall pressure distributions and overall performance of nozzles.The performance of two models has little difference in the vicinity of design point

the axial thrust coefficient reaches 0.96 and thrust vector angle is about 9 degrees at the design point.Through the low Rnp regime

the performance of nozzles show large variation and the difference is obvious between SERN 1 and SERN 2.In general

the performance of SERN 2 is superior to SERN 1.