Transpiration cooling experiments in free-piston shock tunnel HIEST

Kurzfassung

Transpiration cooling technique is one of the most promising candidates as the next‐generation TPS ‐thermal protection system for reentry or planetary entry vehicles. Although many researchers have produced numerous works over these decades to use the technique to cool spacecraft or aircraft components, which are exposed to high heat‐load, such as rocket engines or gas‐turbine blades. Nevertheless, most of the studies were focusing on the applications in a turbulent boundary layer. On the other hand, planetary entry or reentry vehicles have to fly from hypersonic to subsonic speed. Since flight altitude is also changed from the space to the ground, Reynolds number will change from fully‐laminar to fully‐turbulent condition. Moreover, the extremely high flightspeed will produce thermochemical non‐equilibrium flow in the boundary layer. For the application of the cooling technique on reentry vehicle design, it is crucial to address the knowledge about the characteristic of transpiration effects on boundary layer under such the extreme high‐stagnation flow condition. Recent studies were all carried in low‐density flow, or in perfect gas flow (low enthalpy flow), under which flow condition does not agree to real flight condition. The free‐piston shock tunnel HIEST, which can produce high‐enthalpy and high‐density namely high‐Reynolds number test free‐steam suitable for the study of transpiration cooling. The aim of the present research is to obtain transpiration cooling characteristics with a generic flat plate in HIEST under high stagnation enthalpy and pressure condition, which stagnation enthalpy was 4 to 20MJ/kg and stagnation pressure was 12MPa to 60MPa. The transpiration cooling on the flat plate surface was conducted with Helium or Nitrogen gas injection through a porous material located downstream of the leading edge, which material had already used for previous Hypersonic studies. Heat flux distribution on the flat plate was measured along the centerline. The small amount of gas‐injection reduces surface heat flux. Even so, heat flux augmentation was observed with large amount of gas‐injection due to the onset of early transition of the boundary layer.