Experimental Analysis of the Interaction Between a Dual-Bell Nozzle with an External Flow Field Aft of a Backward-Facing Step

Abstract

Previous research on Dual-Bell nozzle flow always neglected the influence of the outer flow on the nozzle flow and its transition from sea level to altitude mode. Therefore, experimental measurements on a Dual-Bell nozzle with trans- (\(Ma_\infty = 0.8\)) and a supersonic (\(Ma_\infty \) = 1.6 & 2.0) external flows about a launcher-like forebody were carried out in the Trisonic Wind Tunnel Munich with particle image velocimetry and the schlieren technique. The sea level mode was investigated in transonic conditions, whereas transition and the altitude mode took place in supersonic conditions. The results show that there is a strong interaction between the nozzle flow and the outer flow in sea level mode, highly dominated by screeching. In contrast, there is no apparent correlation between the nozzle flow and the outer flow in the altitude mode. Transition from sea level to altitude mode shows multiple retransitions over a wide range of nozzle pressure ratios. This is due to an interaction of the nozzle flow with a supersonic expansion about the nozzle’s lip. For the feasibility of the Dual-Bell concept, future research should investigate if a transition in transonic free-stream conditions is possible without the flip-flop effect.