Three-dimensional flow phenomena have been observed in a shock tube experiment for shock waves and vortices by using an interferometric CT (Computed Tomography) technique with a N2 pulse laser. A model with small duct, which has a pair of circular open ends, is introduced in a test section of diaphragmless shock tube, and can be rotated around its central axis to change the observation angle. The projection image of density distribution for each observation angle is obtained by using a fixed Mach-Zehnder interferometer. Three-dimensional density distribution is reconstructed from these projection images. The shock Mach number is 2.3 in nitrogen gas of 19.4kPa initial pressure at the exits of the open ends. The resultant 3-D density flow fields are illustrated by several imaging technique to clarify 3-D features of shock waves, vortices, and their mutual interactions. A computational fluid dynamics (CFD) simulation is also applied to the 3-D flow fields. The CFD results can represent density and another properties in flow fields, and these properties are useful for identifying the phenomena. The mutual validation between the experimental CT density results and these CFD results is discussed. Three-dimensional features of flow fields are investigated in detail by analyzing the experimental CT results with CFD results.
When space vehicles reenter onto the atmosphere with velocity over 10 km/s, radiative heating from the shocked air ahead of the vehicle plays an important role on the heat flux to the wall surface as well as convective heating. So far, spectroscopic study has been developed for temperature measurement of radiation behind strong shock waves. In this paper, CARS method (Coherent Anti-Stokes Raman Spectroscopy) for radiation behind strong shock waves in gases has been applied. The CARS measurement system consists of a YAG laser, a dye laser, and high-sensitivity CCD camera systems. The preliminary tests have been performed for the purpose of detecting CARS signal from strong shock waves with velocity range over 5km/s.