<title>Density field measurement of Mach reflection of shock waves by laser speckle method</title>

Abstract

Density field of Mach reflection of shock waves was investigated by a laser speckle method. A 2D wedge was mounted on the test section of shock tube. When a plane shock wave attack the wedge, shock wave is reflected by the wedge and Mach reflection takes place. Density gradient in the internal region behind the reflected shock wave was measured by this method. The gradient of density plays an important role to determine the reflected shock configuration, especially in weak Mach reflection. Not only the non-uniformity might be a reason 'von Neumann paradox', but also should be important in the case of moderate Mach number. In the present report, density field near the triple point was studied mainly. Optical arrangement is the same as that in Erbeck and Merzkirch. A shock tube and YAG laser were employed in the experiment. The reference and flow fields were recorded in a film. The speckle photographs were processed by auto-correlation analysis by a computer. Displacement of speckle pattern was convected to the density by using a deflection angle-density gradient relation. It was found that the distribution of density field has large gradient near the reflected shock wave. Experimental density fields were compared with numerical results.