Control of Operation Mode Transition in Dual-Bell Nozzle with Film Cooling

In addition to aspiration drag, the advantages gained by using a dual-bell nozzle, in practice are circumvented with a sudden temporal decrease of the specific impulse during operation mode transition occurring not at the optimal conditions. Practical transition from a low to a high altitude operation mode occurs earlier than a vehicle reaches optimum transition point. The introduction of film-cooling flow into the nozzle has beneficial effects for the thrust and thermodynamic performance. The influence of the film-cooling parameters on the nozzle operation mode transition is investigated. It is found that when the certain conditions of the introduced film-cooling flow are met, the mode transition of the dual-bell nozzle shifts to the higher values of the nozzle pressure ratios, thus bringing it closer to the optimum transition point. It is understood that an interaction of the film-cooling and the main jet creates high pressure regions in the vicinity of the inflection point, which in turn increase or decrease the transition pressure ratio. Axial momentum in the radial direction at the nozzle exit alters the speed of a separation region movement.