Schlieren Photography of N-Waves about a Focus

Abstract

The schlieren method is a relatively old technique. The first system has been accredited to Leon Foucault. Foucault designed the system in 1858 as a means of quality control in the manufacture of large objectives. Known as the "Foucault knife-edge test," this system is still in use and remains as the basic form of schlieren systems. The schlieren method and the closely related shadow-graph technique have been used in many areas of research and quite extensively in the field of aerodynamics. These methods are commonly used in conjunction with wind tunnels to study areas of compression and turbulence around test models. A wide variety of disturbances may be studied since, theoretically, any inhomogeneities in a transparent medium may be visualized. More recently studies have been made in the field of heat exchange and hydrodynamics. However, in acoustical studies, the schlieren and shadow-graph techniques have not been widely employed. The aim of this project was to develop a schlieren system capable of acoustical studies. As an object of investigation, N-wave focusing was chosen. The specific goal of the project being, a series of photographs of N-waves as they are brought to a focus.