CBD(Center Body Diffuser) is one of the latest technologies in high altitude simulation test facilities. This is one of supersonic diffuser that uses a strong momentum of high-speed and high-pressure fluid injected from the nozzle to drop pressure of the chamber surrounding the nozzle, decelerate the flow, and discharge it. To investigate the performance characteristics of the center body diffuser, numerical analysis was performed. The numerical results are verified by comparing the results of the wall pressure test of the sub-scaled diffuser. In this study, the effect of the center body position on the diffuser characteristics was investigated, and the effect of the multi cone type center body inspired by the ramjet inlet was also investigated. And burnt gas flow analysis for the design of CBD cooling system was conducted. The results of the study are summarized as follows.

1) As the position of the center body in the CBD moves to the downstream of the Diffuser, the CBD tends to start at a lower operating pressure because the plume is formed without being disturbed by the structure and has a large momentum.

2) However, In the vicinity of (Ld/Dst) = 1, the starting pressure was maximum due to incomplete development of supersonic flow, Even when diffuser was started, vacuum pressure was about 200 Pa higher than in the other cases.

3) As the center body position in the CBD moves to the downstream of the diffuser, the strength of the collision with the CB becomes stronger, so that the radial momentum becomes large and the supersonic flow flows along the inner wall. On the other hand, if CB is located upstream of the diffuser, it flows in the opposite direction to the CB.

4) In the case of multi cone type instead of single cone type, the supersonic flow is smoothly discharged and the starting pressure is lowered by 2 bar. However, the vacuum chamber pressure increased by 200 Pa due to the reduction of the entrainment phenomenon near the entrance of the vacuum chamber.

5) The simulated altitude changes depending on the change of temperature at combustion chamber and the change of properties of the working fluid.

6) The upstream of the diffuser is a supersonic region, so the temperature is relatively low, and at the downstream of the diffuser the temperature rises close to the combustion chamber temperature.