A Simple Method for Simultaneous Projection of a Schlieren Image on a Viewing Screen and into a Camera

Abstract

The toepler schlieren system of wind tunnels is usually designed in such a way that an image of the flow in the test section can be formed in a camera for taking flow pictures. For visual observation, a mirror is inserted in the light beam and the image is projected on a screen. When a photograph or film record of the flow is desired, the mirror is removed by some quick-acting mechanism to allow the light beam to enter the camera. Especially in the case of non-steady flows, the time lag involved in removing the mirror can prove to be a drawback. An interesting pattern observed upon the screen may have vanished by the time the light beam is switched over to the camera. At the same time the image disappears from the screen, leaving the operator in doubt whether or not the pattern lasted long enough to be recorded by the camera. In this note a very simple arrangement of the schlieren system is described, which gives simultaneously an image on the viewing screen and in the camera. So far as the author knows, it is not applied elsewhere. The method consists of the use of a mirror knife edge instead of the usual knife edge.

Multiple Simultaneous Imaging Schlieren System

“…T HE NEED for simultaneous use of more than one type of camera to record Schlieren images of aerodynamic phenomena has led a recent investigator' 1 ' to employ a system in which an additional image was reflected from the Schlieren stop when it intercepted a deflected beam. This note describes an alternative arrangement capable of producing at least four images, although in its present form it is only designed to produce three.…”