Experimental and Numerical Study on Performance of Extendible Nozzle for Altitude Compensation

An extendible nozzle for altitude compensation is considered to be a feasible device to improve the performance of booster engines because it can provide higher thrust at sea level and higher specific impulse in vacuum. 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. Based on the experimental results of the firing tests using a sub-scale model, the characteristics of thrust coefficient, the nozzle axial load, and the nozzle side load affected by the nozzle flow transition are examined. The backflow of combustion gas through the gap between the fixed nozzle and the nozzle extension was also examined with use of CFD analysis. As results, disadvantages in the nozzle performance and the nozzle loads in case of improper nozzle deployment condition are clarified.