Schlieren visualization of a stratified flow around a cylinder

Description of different modification of schlieren techniques is presented. The methods are based on Maksoutov’s scheme of the schlieren mirror instrument with an illuminating slit and a different cutting diaphragm, specifically with Foucault knife, filament or grating. Depending on a slope of the slit to the vertical both black-and-white and colour schlieren images of a stratified flow are produced. Simple colour schlieren method using natural dispersion of white light in a stratified medium is described. ‘Natural rainbow’ schlieren image of a stratified flow is formed when an illuminated slit is placed horizontally and regular grating is used as a light cutting element. The method is characterised by a high spatial and temporal resolution and by a wider dynamic range than the traditional one. Examples of black-and-white and colour images of a stratified flow near a towing cylinder are presented. © 1999 The Visualization Society of Japan and Ohmsha, Ltd.