NUMERICAL INVESTIGATION ON SHEAR LAYER DEVELOPMENT IN A DUAL-FUEL MODEL ROCKET NOZZLE

Dual throat nozzle is a concept suited for altitude adaptation and can be employed for tripropellant rocket engines, as it features two annular combustion chambers that can burn two fuels separately. Its dual-fuel mode operation produces a shear layer between the interfaces of the hot gas plumes. This shear layer is a mixing zone influenced by shock expansion wave interaction that can influence performance of the nozzle. Numerical studies are conducted for a two-dimensional planar dual throat nozzle model to analyze the shear layer formed in expanding supersonic flow conditions. Simulations are performed for both cold and hot flow conditions. Air is considered the working fluid in the two chambers for cold flow conditions. For hot flow conditions equilibrium reaction products of liquid oxygen- hydrogen in the inner chamber and liquid oxygen-methane in the outer chamber are considered. The growth of shear layer is found to be small while turbulent intensity seems to be reduced at high convective Mach numbers. The velocity profile downstream of the inner nozzle shows self-similarity, and the performance of the nozzle is comparable with that of a conventional nozzle. A detailed analysis of shock wave-shear layer interactions, variation in the location, and shape of flow structure due to the difference in working fluids are presented.