LOX / CH 4 Hot-Flow Testing of Dual-Bell Nozzles with Rapid-Expansion Extension

Hot-flow testings with subscale dual-bell nozzle models were conducted. The primary nozzle model had a relatively large initial expansion angle in the extension nozzle section. The propellant was liquid oxygen and gaseous methane. Wall distributions of pressure, temperature, and heat flux distributions along the extension nozzle were measured to characterize the effect of the mixture ratio and combustion chamber pressure on the separation transition. The wall pressure for the primary test model indicated that the separation transition took place at nearly a constant nozzle pressure ratio and independently of the mixture ratio. Differently, a test model with a smaller expansion angle, which was also tested for a comparison, showed that the separation transition took place dependently on the mixture ratio. Comparison of the separation transition condition with some existing criteria found that one of the causes of the dependency on the mixture ratio was related to the separation pressure in the inflection region. Additionally, strong hysteresis was observed for the test model with a smaller extension angle. The heat flux transducer data indicated that the wall heat flux at the inflection point at the separation transition had a linear relationship with the mixture ratio. Presented as Paper 2015-4156 at the 51st AIAA/ASME/SAE/ASEE Joint Propulsion Conference (AIAA Propulsion and Energy 2015), Orlando, FL, 27-29 July 2015