摘要: In the high-enthalpy shock tunnel HIEST, a test campaign to investigate the hypersonic boundary layer was conducted. The second-mode instability in the boundary layer was observed on a cone with a half angle of 7-degrees and a tot... 展开 In the high-enthalpy shock tunnel HIEST, a test campaign to investigate the hypersonic boundary layer was conducted. The second-mode instability in the boundary layer was observed on a cone with a half angle of 7-degrees and a total length of 1.1 m using a three-channel focused laser differential interferometer (FLDI). The laser focal points were placed at 610 mm, 805 mm, and 910 mm from the cone's nose tip. The distance between the laser focal points and the cone surface was adjusted to 1 mm. A comparison test utilizing dry air and pure nitrogen as test gases was carried out to observe the test gas effect. Both tests had the same stagnation enthalpy of 9.4 MJ/kg and unit Reynolds number of 2.4×10~6/m. In comparison to pure nitrogen, the growth of disturbances appeared to be the second-mode instability was slower in dry air. In order to observe the enthalpy effect, series of shock tunnel tests were conducted with different stagnation enthalpies from 3.4MJ/kg to 9.5MJ/kg, while maintaining a constant unit Reynolds number approximately Re=2.4×10~6/m, and the effect of stagnation enthalpy was seen in two test gas, dry air, and pure nitrogen. The findings demonstrated that the onset of the second-mode that appeared to be a secondary mode instability in the dry air under the same unit Reynolds number conditions was delayed with increasing enthalpy. On the other hand, however, no clear effect of enthalpy was observed in pure nitrogen. 收起