A numerical study has been conducted to investigate flow and cooling characteristics of diffuser for high altitude simulation. Properties of burnt gas have been included to provide basic information which is the essential design parameter of the diffuser. Since the burnt gas with high temperature flows inside the diffuser, the most important thing is a thermal problem. Firstly, the wall of the diffuser was analyzed as adiabatic condition in order to find a high-temperature region and investigate flow characteristics. Secondly, the wall of the diffuser was added on the cooling channels to confirm the cooling characteristics of the diffuser.
The diffuser is operating at higher than operating pressure of 40 bar. When operating pressure is 30 bar, the plume was contracted and the vacuum pressure wasn''t enough to simulate the high-altitude condition. After the startup of the diffuser, there were high temperature regions over 2000 K especially near wall and subsonic diffuser. If the diffuser did not operate normally, gases of high temperature may be entrained to the vacuum chamber. After the normal startup, vacuum chamber was choked by supersonic flow and only the small amount of high-temperature gas was entrained.
It was observed that change of (L/D)st was correlated with the creation of Mach disk. As the length of the subsonic diffuser(Ls) is shorten, the pressure was rapidly recovered. For this reason, it was expected to make big noise and shock inside the diffuser. In other words, length of each section must have sufficient length for stable operation of the diffuser.
If the cooling system of the diffuser is added, flow velocity is increased and pressure is rapidly recovered due to the decreased static temperature. On the other hand, the pressure of the vacuum chamber is not affected by adding cooling system.
The heat flux in the supersonic flow was proportional to P^0.8. However, the heat flux in the subsonic flow did not show the same tendency. So, additional studies will be needed as a future work. When rapid pressure fluctuation such as Mach disk and shock train is appeared in the diffuser, the heat flux also appears to be a high value.