Experimental investigation of flow separation in a planar convergent-divergent nozzle

Under the conditions of nozzle pressure ratio (NPR) of 2.79, 2.82 and 2.95, the flow field was observed by dynamic pressure measurement and focusing schlieren technique, and the flow separation characteristics of a planar convergent-divergent nozzle were studied. The results show that as the NPR increases, the nozzle flow structure changes from asymmetric to a symmetrical configuration. Under the condition of NPR=2.79, the flow in the nozzle goes obviously downward to the bottom wall of the nozzle, and the restricted shock separation (RSS) occurs on the bottom wall; under the condition of NPR=2.82 and NPR=2.95, the flow in the nozzle tends to be symmetrical, RSS appears on both the top and bottom walls. Based on spectrum analysis, it is found that there is obvious low-frequency oscillation characteristics near the separation point.