SCHLIEREN IMAGING METHOD AND ITS APPLICATION FOR VISUALIZING OF SOME PHYSICAL PROCESSES V. Ohanesjan, R. Popeski-Dimovski, and S. Topuzoski

Schlieren imaging as technique for visualization of nonhomogeneous regions. Word “Schlieren” origins from old German, meaning bits or pieces. We present here a theoretical explanation of the schlieren imaging, and a simple experimental procedure IX Conference of the Society of Physicists of Macedonia September 2012, Ohrid, R Macedonia Shimmering mirages on a hot road or optical distortions caused by the hot air from jet engine are everyday life examples of schlieren effect. Introduction Fig. 1 Fig. 2Fig. 3 During the time, many different apparatus for Schlieren imaging have been developed (two mirrors, one mirror, two lenses (Toepler), one mirror). Our schlieren system is with two lenses. “convergent”

First observations on schlieren effect were reported by Hooke and Huygens in XVII century IX Conference of the Society of Physicists of Macedonia September 2012, Ohrid, R Macedonia Historical facts August Toеpler ( )  Gave a name to this technique (Schlieren);  First basic apparatus for flow visualization by using a knife – edge;  “Classics of Exact Science” ; In present time, the most significant names in this field of physics are Leonard M. Weinstein and Gary S. Settles. Fig. 4 Hubert Schardin was recognized as a modern pioneer of the color schlieren technique. Fig. 5

Human eyes and CCD detectors are only color and intensity sensitive IX Conference of the Society of Physicists of Macedonia September 2012, Ohrid, R Macedonia The light wave changes its phase during propagation in a transparent medium with refractiv index gradient. Using the schlieren optical method the phase variation is transformed into intensity variation, allowing us to detect refractive index gradient. Gary S. Settles has made a lot of outdoor observations on different phenomena. Application of the method to liquid membranes, sonar pulses, optically transparent polymers and polymeric foils. Schlieren method and application Fig. 6 Fig. 7 M. Weinstein had transformed an telescope into schlieren apparatus.

Two convergent plano – convex lenses with 9 cm diameter and 50 cm focal length IX Conference of the Society of Physicists of Macedonia September 2012, Ohrid, R Macedonia Optical fiber from Oceans Optics Spectrometer as a point light source. Micrometer diaphragm as a knife – edge. Nikon d 5000 with AF-S Nikkor lens mm. Computer software: Camera Control Pro 2 and Capture NX 2 Experimental setup Fig. 8 Fig. 9

IX Conference of the Society of Physicists of Macedonia September 2012, Ohrid, R Macedonia The light rays propagating in medium with refractive index gradient bend fractionally to the regions of greater index due to the change of the speed of the light. Theoretical explanation

IX Conference of the Society of Physicists of Macedonia September 2012, Ohrid, R Macedonia Fig. 10

IX Conference of the Society of Physicists of Macedonia September 2012, Ohrid, R Macedonia where Fig. 11

IX Conference of the Society of Physicists of Macedonia September 2012, Ohrid, R Macedonia Experimental results Knife - edge orientation Fig. 12 : Horizontal temperature gradient due to the lighted match, and horizontally orientated knife edge. Fig. 14: Turbulent air flow. Here in this case is no preferred axis, because of that knife edge orientation does not influence significantly. Fig. 13 : Horizontal temperature gradient, and vertically orientated knife edge.

IX Conference of the Society of Physicists of Macedonia September 2012, Ohrid, R Macedonia Image digital processing Fig. 15: Just captured image. Fig. 16: Post processed image with Capture NX2

IX Conference of the Society of Physicists of Macedonia September 2012, Ohrid, R Macedonia Electrostatic discharge Other examples Fig. 17: Human breathing. Fig. 18: Electrostatic discharge between the electrodes of the high voltage supply.

IX Conference of the Society of Physicists of Macedonia September 2012, Ohrid, R Macedonia Conclusion We succeeded to set up a schlieren system with the optical elements we have in our laboratory and tested its sensitivity. We have observed and recorded by camera: laminar and turbulent gas flow, an electric discharge in air, temperature gradient, breathing and heat flow from palm. These experiments are also valuable from the educational point of view, because they serve as an introduction in optical design and alignment for undergraduate students. Some of the experimental processes visualized by this method can help in studying the corresponding physical phenomena. Part of this paper was presented on the student competition Primatijada 2012, and was awarded as a best student project in physics.

IX Conference of the Society of Physicists of Macedonia September 2012, Ohrid, R Macedonia Thank you for your attention !