Design and Performances of the Dual-Bell Nozzle

The dual-bell nozzle is an innovating-technology of Rocket Nozzles; it is one of the most promising concepts for the altitude-compensating nozzles. Indeed, the flow in this type of nozzle has the ability to auto-adapting for both operating modes (at low and high altitude) without mechanical activation. The principle is theoretically simple but structural forces involved can be significant. In this study, a numerical method for the design of this type of nozzle is developed. To start the calculation, an initial line is generated using the sonicline calculation method. Then the inverse method of characteristics is applied to generate the base nozzle profile. The nozzle extension contour is calculated to give a constant wall pressure. This is achieved by using the direct method of characteristics applied for a centered expansion wave (Prandtl-Meyer wave) that the intensity is P-2/P-1 at the junction. As the profile is generated, a study of the thermodynamic-parameters evolution (pressure, Mach number, temperature, density.) and aerodynamic performances (thrust, specific impulse...) is conducted. The obtained-results are compared to those of studies that have been done by: the National Office of Studies and Aerospace Research (ONERA-France) and the National Space Research Center (CNRS). However it is important to know that the comparison of different configurations (Ideal, TIC and Dual-Bell) is made in terms of performances and weight. This comparison was satisfactory sight the results agreement.