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 sonic-line 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 P2/P1 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.