Flow Visualization and Density Measurement of Compressible Flows
by a Laser Speckle Method
Issue title: International Conference on Optical Technology
and Image Processing in Fluid, Thermal, and Combustion Flow, Yokohama, Japan,
December 1998
Affiliations: Faculty of Engineering, Saitama University,
Shimo-Okubo 255, Urawa, Saitama, 338-8570, Japan | Kanto Auto Works Ltd., Yokosuka, Kanagawa, 237-8585,
Japan
Abstract: Laser speckle method is a well known technique that is useful for
both visualization and quantitative measurement. This technique was applied to
the density measurement of Mach reflection of shock waves in the present
experiment. The Object of the measurement is the density field of simple Mach
reflection in relatively low shock Mach number. The non-uniform flow field is
divided into three regions by incident, Mach and reflected shock waves. A shock
tube was employed in the present experiment. Wedges of 20 degrees and 45
degrees were placed in the test section. YAG laser was employed as a light
source. Speckle photograph was taken by a digital still camera. Simple
subtraction between the reference and flow images shows a shock pattern and a
degree of the correlation of speckle pattern in the flow field. Thus, we can
obtain a visualized flow image showing a configuration of Mach reflection from
speckle photograph. Speckle photographs which was obtained in the experiments
were processed with cross-correlation method. A reconstructed density gradient
vector map of Mach reflection was obtained. Comparing the experimental result
with numerical one, the measured density gradient shows a good agreement with
theoretical prediction.
Keywords: laser speckle photography, density measurement, compressible flow, shock tube
