Digital holographic interferometry in high-speed flow research

Abstract

A dual reference beam, plane wave, digital holographic interferometric system has been developed. It has also been applied as a non-intrusive optical diagnostic tool to a high speed flow. Quantitative density data has been extracted automatically by first generating phase-stepped interferograms. These were then digitized via a charge coupled device (CCD) camera and digitally post-processed within the memory of a computer. The results obtained have mapped an instantaneous 3-D density distribution of an unsteady flow field onto a 2-D projection plane. They show quantitatively the interaction between a shock wave and a turbulent boundary layer. A description has also been made showing how the dual reference beam technique can be extended to provide a quantitative density measurement of turbulent and unsteady flow structures.