New Dimension in the Schlieren Technique: Flow Field Analysis Using Color

Abstract

The various techniques for introducing color into a schlieren system were explored, and all of them were found to have drawbacks such that the added dimension of color in a schlieren has never been utilized for extensive quantitative measurements. An entirely new technique using a diffraction grating to produce the color has been introduced as a modification of the conventional schlieren system. It provides solutions to the problems of sensitivity, range of measurement deflection and undesirable effects of diffraction which have limited the usefulness of color systems in the past. Methods for analyzing a conventional schlieren have been modified for the analysis of a color schlieren result. Surface pressures and flow field analysis for some simple two-dimensional airfoil shapes have been obtained by these color techniques developed here, and the results compare very well with theoretical pressure calculations.

Near-field imaging techniques for surface inspection

“…[28][29][30][31] A typical example is the well-known shadowgraph method for visualization of processes in transparent media, which is closely related to the schlieren technique. [32][33][34][35][36][37][38] The shadowgraph technique images the field distribution of the geometrical shadow of the object. For this purpose either an intermediate screen might be used, or the shadow is treated as an air image and imaged directly.…”

A four colours line grid schlieren method for quantitative flow measurement

“…Besides, for a long time, methods are known to gain quantitative results with the support of schlieren optics. The application of coloured filters is summarized by Schardin (1941), Holder andNorth (1956), Wrist (1957), Maddox and Binder (1971), Settles (1982) and Oertel and Oertel (1989). There, instead of a knife edge, filters with a coloured pattern are frequently used through which the light, depending on the spot at * Present address: Motoren-und Turbinen-Union Miinchen GmbH, D-8000 Mtinchen 50, E R.Germany…”