Active Control of Dual-Bell Nozzle Operation Mode Transition by Film Cooling and Mixture Ratio Variation

A numerical study is conducted to investigate the impact of a film-cooled dual-bell nozzle extension on its operation mode transition behavior. Therefore, unsteady Reynolds-averaged Navier–Stokes simulations of the transition process between the sea level and altitude modes are carried out. The investigated dual-bell nozzle model is fed with hot gas by a combustion chamber using liquid oxygen as oxidizer and gaseous hydrogen as fuel. Upstream of the dual-bell nozzle contour inflection, gaseous hydrogen is injected as cooling fluid for the nozzle extension wall. The numerical studies yield a clear impact of the cooling fluid mass flow rate on the transition nozzle pressure ratio of the dual-bell nozzle. The increase of the cooling fluid mass flow rate leads to a shift of the dual-bell transition nozzle pressure ratio to lower values. Furthermore, the impact of the combustion chamber mixture ratio on the dual-bell operation mode transition is investigated. A clear shift to lower transition nozzle pressure ratio values due to higher propellant mixture ratios can be observed. A combination of the two effects is introduced for an active control of the dual-bell operation mode transition.