LOX/CH4 Hot Firing Dual Bell Nozzle Testing: Part II - Characteristics of Combustion Instability and Heat Flux -

A sub-scale hot-flow testing on the dual-bell nozzle test model was conducted as a cooperative research project between the Japan Aerospace Exploration Agency (JAXA) and the German Aerospace Center (DLR). This paper describes test results obtained with the test model designed by JAXA which had a relatively large initial expansion angle in the extension nozzle. The testing was implemented at DLR in Lampoldshausen, Germany. The propellant was a combination of liquid oxygen and gaseous methane. With the test model designed by JAXA, the hot-flow test data with respect to the distributions of pressure, temperature, and heat flux on the extension nozzle wall was obtained, and the effect of mixture ratio and combustion chamber pressure on the separation transition was characterized. The measured wall surface pressure indicated that the separation transition took place irrespective of the nozzle pressure ratio, and this was attributed to that the large initial expansion angle of the extension nozzle and the designed nozzle contour which had the positive pressure gradient governed the separation transition mechanism: the separation point jumped suddenly from the inflection point to the extension nozzle exit. Other characteristics with respect to the heat flux and combustion instability are also discussed.