SCHLIEREN IMAGING METHOD AND ITS APPLICATION FOR VISUALIZING

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

Introduction • Schlieren imaging as technique for visualization of nonhomogeneous regions. • Word “Schlieren” origins from old German, meaning bits or pieces. • Shimmering mirages on a hot road or optical distortions caused by the hot air from jet engine are everyday life examples of schlieren effect. • We present here a theoretical explanation of the schlieren imaging, and a simple experimental procedure. Fig. 2 Fig. 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” 21. 09. 2012 Fig. 1 IX Conference of the Society of Physicists of Macedonia 20 -23 September 2012, Ohrid, R Macedonia

Historical facts • First observations on schlieren effect were reported by Hooke and Huygens in XVII century. • August Toеpler (1836 -1912) § Gave a name to this technique (Schlieren); § First basic apparatus for flow visualization by using a knife – edge; § “Classics of Exact Science” ; • Hubert Schardin was recognized as a modern pioneer of the color schlieren technique. Fig. 4 • In present time, the most significant names in this field of physics are Leonard M. Weinstein and Gary S. Settles. Fig. 5 21. 09. 2012 IX Conference of the Society of Physicists of Macedonia 20 -23 September 2012, Ohrid, R Macedonia

Schlieren method and application • Human eyes and CCD detectors are only color and intensity sensitive. • 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. Fig. 6 • M. Weinstein had transformed an telescope into schlieren apparatus. Fig. 7 21. 09. 2012 IX Conference of the Society of Physicists of Macedonia 20 -23 September 2012, Ohrid, R Macedonia

Experimental setup • Optical fiber from Oceans Optics Spectrometer as a point light source. • Two convergent plano – convex lenses with 9 cm diameter and 50 cm focal length. • Micrometer diaphragm as a knife – edge. • Nikon d 5000 with AF-S Nikkor lens 55 -200 mm. Fig. 8 • Computer software: Camera Control Pro 2 and Capture NX 2 Fig. 9 21. 09. 2012 IX Conference of the Society of Physicists of Macedonia 20 -23 September 2012, Ohrid, R Macedonia

Theoretical explanation • 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. 21. 09. 2012 IX Conference of the Society of Physicists of Macedonia 20 -23 September 2012, Ohrid, R Macedonia

Fig. 10 21. 09. 2012 IX Conference of the Society of Physicists of Macedonia 20 -23 September 2012, Ohrid, R Macedonia

Fig. 11 where 21. 09. 2012 IX Conference of the Society of Physicists of Macedonia 20 -23 September 2012, Ohrid, R Macedonia

Experimental results • Knife - edge orientation Fig. 14: Turbulent air flow. Here in this case Fig. 12 : Horizontal temperature Fig. 13 : Horizontal temperature is no preferred axis, because of that knife gradient due to the lighted match, gradient, and vertically orientated edge orientation does not influence and horizontally orientated knife edge. significantly. edge. 21. 09. 2012 IX Conference of the Society of Physicists of Macedonia 20 -23 September 2012, Ohrid, R Macedonia

• Image digital processing Fig. 15: Just captured image. 21. 09. 2012 Fig. 16: Post processed image with Capture NX 2 IX Conference of the Society of Physicists of Macedonia 20 -23 September 2012, Ohrid, R Macedonia

• Other examples Electrostatic discharge Fig. 17: Human breathing. 21. 09. 2012 Fig. 18: Electrostatic discharge between the electrodes of the high voltage supply. IX Conference of the Society of Physicists of Macedonia 20 -23 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. 21. 09. 2012 IX Conference of the Society of Physicists of Macedonia 20 -23 September 2012, Ohrid, R Macedonia

Thank you for your attention ! 21. 09. 2012 IX Conference of the Society of Physicists of Macedonia 20 -23 September 2012, Ohrid, R Macedonia