Schlierenvisualisering

Schlierenvisualisering, often simply referred to as schlieren, is an optical technique used to visualize flow patterns in transparent media, such as air or liquids, that are not ordinarily visible to the naked eye. It works by detecting variations in the refractive index of the medium. These variations are typically caused by differences in density, temperature, or pressure. The fundamental principle relies on the fact that light bends (refracts) as it passes through regions with different refractive indices.

A basic schlieren setup involves a light source, a focusing element (often a spherical mirror or lens), a knife-edge or razor blade positioned at the focal point, and an observation screen or camera. Light from the source is collimated into a parallel beam, passes through the medium being studied, and is then focused back by another optical element. At the focal point, the knife-edge is placed to block or partially block the light. If there are no density gradients in the medium, the light rays will all converge at the focal point. However, if there are density gradients, the light rays will be deflected.

When the deflected light rays hit the knife-edge, some will be blocked, while others will pass. This differential blocking creates a contrast on the observation screen, revealing the outline of the density variations. The resulting image shows streaks or patterns corresponding to areas of varying refractive index, making phenomena like shock waves, heat plumes, or turbulent flow visible. Schlieren is a powerful tool in fields such as aerodynamics, combustion research, and fluid dynamics for non-intrusively observing and analyzing fluid behavior.