In this study, the performance of the E-D nozzle according to the basic characteristics and design variables was evaluated and the possibility of the shape combined with the dual bell nozzle of the altitude compensation nozzle was studied.
In the case of a dual bell nozzle, control of the transition plays a significant role in the dual bell nozzle because the nozzle performance varies greatly depending on when the transition occurs. Therefore, this study focuses on how the transition characteristics change when analyzing the shape combining a dual bell nozzle and an E-D nozzle. As a result of the numerical analysis according to the altitude, it was verified that when the dual bell nozzle is applied to the KSLV-II 1st stage engine, the transition occurs at an altitude of 7 km, whereas when the E-D nozzle is applied to the DB0724 shape, the transition occurs at 10 km. The reason for the increase of the transition altitude is considered to be that the flow in the nozzle over-expands due to the application of the pintle concept of the E-D nozzle in the dual-bell nozzle, which leads to an increase in the ideal expansion altitude. In fact, it was numerically verified that the nozzle exit pressure is also lowered when applying the E-D nozzle. The change of the transition altitude by applying the E-D nozzle concept can be utilized as a control method to control the transition altitude of the dual bell nozzle.
The dual bell nozzle has a limitation that the weight of the nozzle is increased due to the addition of the extension part shape. In order to overcome this limitation, we applied the E-D nozzle concept to the dual bell nozzle to understand the possibility of payload gain according to the nozzle length reduction. As a result of comparing the total specific impulse up to 54 km altitude at which the KSLV-II 1st stage engine is separated, it is possible to see the possibility of payload gain in terms of achieving the same performance and reducing the nozzle length. However the total specific impulse up to 54 km was lower than that of the dual bell nozzle applied only to the KSLV-II 1st stage engine in the previous study. Although the total specific impulse was lower according to the performance loss interval at low altitudes, the performance gain was higher than that of the KSLV-II 1st stage in the high altitude region of 22 km or more.