Time-Developing 3D-CT Measurement of Shock Waves and Supersonic Density Flow Field

Abstract

In the supersonic and hypersonic flow diagnostics, density field observation has been one of the main targets of experimental fluid-dynamic researchers. From the very beginning of twentieth century, flow visualization methods by optical photographs have been investigated and the pictures by shadowgraph, schlieren method, or interferometry have been widely utilized to the qualitative density flow field clarification. As these methods still give strong power to the researchers of fluid dynamics, new diagnostic technology is dramatically developing together with new optical and digital image instruments and high-power PC. Above all, computed tomography (CT) of the supersonic density flow field including the shock waves is typical and rapid-developing diagnostics with digital image technology. The hardware and software/algorithm for optical CT suitable to the high-speed flows should be investigated in the next decade. In the present paper, the author deals with two CT diagnostic methods, those are density field measurement by CT with traditional Mach-Zehnder interferometry (LICT) for discharging shock wave and vortex, and density gradient field measurement by CT with background-oriented shclieren (BOS) method of colored-grid background (CGBOS) in a supersonic wind tunnel. Furthermore, in each method, the novel time-developing three-dimensional CT measurement (4D-CT) experiments of LICT and CGBOS with high-speed camera are presented. These experiments and CT reconstruction have been successfully done by the author (mainly as Prof. in Chiba Univ.) and Prof. M. Ota and our laboratory students in Chiba University.