Test flow conditions for the expansion tube experiment

To investigate a hyper velocity flow field characteristics around a vehicle, such as a super-orbital atmospheric re-entry vehicle, the high enthalpy facilities are utilized. The expansion tube is among them. In this paper, the characteristic flow condition generated in the expansion tube was investigated to evaluate the test time period and the test flow condition realized in the expansion tube. For the investigation, the pitot pressure, the static pressure, the shock speed, and the flow field image around the cylindrical pitot pressure probe were measured, and several flow conditions ranging from 5.75 [km/sec] to 11.8 [km/sec] of the final shock speed are utilized. In the temporal pitot pressure history, the secondary pitot pressure jump indicates the contact surface arrival. This fact is also confirmed through observation of the flow field around the cylindrical pitot probe. For the highest flow velocity case, the measured static and pitot pressures after the final shock wave and the contact surface arrival time agrees with the ones estimated with the simple theoretical method assuming equilibrium flow, and the test period estimated with the theoretical method also agrees with the test time period determined experimentally. However, for the medium flow velocity cases, the present simple estimation method must be improved, especially including the effect of the boundary layer development.