A CONTRIBUTION TO THE THEORY OF SCHLIEREN SENSITIVITY AND QUANTIATIVE EVALUATION
DIRECTORATE OF ENGINEER DEVELOPMENT OTTAWA (ONTARIO)
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Detectors used to evaluate schlieren images have a response proportional either to the illumination or to the logarithm of the illumination. Sensitivity point functions appropriate to both kinds of response are defined analytically. These functions are well defined even in the presence of optical system imperfections and are not referenced to the clear field illumination. By the choice of an appropriate system configuration, either function can be reduced to a constant. It is shown that, in principle, the light deviation values required for quantitative evaluation can be found by subtracting out the illumination increments due to diffraction and other system errors. A qualitative treatment of schlieren diffraction from the point of view of the Thomas Young theory is given. A technique is described for obtaining a stigmatic source image with an offset two-mirror schlieren system. A simple method for obtaining simultaneous vertical and horizontal knife-edge schlieren pictures is given. A means for magnifying sensitivity without the use of long focal length mirrors is described. A new method for measuring gas temperatures, which involves crossing a color schlieren system with a spectrograph, is described.
- Test Facilities, Equipment and Methods