Experimental Study on Transitional Phenomena of Extendible Nozzle

An extendible nozzle is considered to be a feasible device to improve the performance of booster engines because it has possibilities to provide altitude compensation and to achieve higher specific impulse. The booster engine with the extendible nozzle has to deploy its nozzle extension on engine firing. For the design of the extendible nozzle including its driving mechanics, it is required to clarify the transitional phenomena during the nozzle deployment. In order to investigate the transitional phenomena, firing tests using a sub-scale model were carried out on a high altitude test stand. In the firing test, the nozzle extension was sustained at a fixed position by supporting rods and the ambient pressure was varied to simulate an altitude change. In order to simulate the nozzle deployment, also the position of nozzle extension was adjusted by replacing the supporting rods. The nozzle extension was sustained at 57%, 67%, 77%, 87%, and 100% deployed positions. The axial load and side load acting on the nozzle extension were evaluated quantitatively by using small load cells installed in each supporting rod, and in addition, the distributions of wall pressure and heat flux along the inner wall of the nozzle extension were measured. Based on the experimental data, the transitional phenomena were investigated in both the mechanical and the thermal aspects. As results, the mechanical and the thermal conditions which can be critical in the design of the extendible nozzle were provided.