Seminars

Due to the development of reusable space transportation systems, the configuration of modern launch vehicles has been changed from serial to parallel staging. Because of security reasons the main stage engine is ignited before the booster stage. Thus the main engine has to operate over a wide range of altitude from sea-level up to almost vacuum conditions. To avoid flow separation of the highly over-expanded nozzle flow at low altitude, the area ratio of the nozzle is limited. A larger area ratio in high altitude would lead to a payload increase. The dual bell nozzle is an altitude adaptive nozzle concept, which combines a low area ratio for low altitude with an high area ratio for high altitude operation. The base nozzle is linked to the nozzle extension by an abrupt change of the wall angle. The contour inflection forces the flow to a controlled and symmetrical flow separation in sea-level mode. During ascend of the launcher the ambient pressure decreases and at a certain altitude the transition to altitude mode takes place. Due to the high area ratio of the nozzle extension and the resulting further expansion, the performance at high altitude is increased.  Due to the controlled and symmetrical flow separation, both operation modes of the dual bell nozzle are uncritical. The transition of the flow separation from one mode to the other is of interest and detailed experimental and numerical investigations were conducted at the German Aerospace Center in Lampoldshausen.