The tests with N2 did not produce any visual indication of the presence of fluid motion other than the decay of the buoyant flow present before the drop. Since N2 is not a radiating gas, this is in accordance with the proposal outlined above. Figure 3 shows an interferometer image of the flow in SF6 at 2 atm taken near the end of the drop test. The large deformation of the fringes in the right half of the frame denote a sharp density gradient and the presence of flow. Interferometer image of radiation-driven flow at g taken near end of drop period.
Fringes are parallel lines when no flow is present.
Although the CO2 did not exhibit as much flow as SF6, tests conducted at pressures above 2 atm. revealed a significant amount of fluid motion. In fact, CO2 tests and N2 tests performed at the same Grashof number were noticeably different. Figures 4 and 5 show interferometer images from CO2 and N2 drop tests, respectively, taken near the end of the drop. The CO2 image shows several regions where fringe deformation is significant, while in the N2 test only minimal fringe deformation is observed. Interferometer image of radiation-driven flow at g taken near end of drop period.