Measurement of the air density gradient in transonic flows by the schlieren - speckle photography technique

This paper presents the description of two non-intrusive optical measurement techniques, which based on refraction and deflection of light rays. These techniques are the Schlieren method and the speckle photography. Especially the latter one have been gain an interesting recently due to dynamic development of computer techniques and digital photography. One of the important parameters in speckle photography is the resolution of the CCD chip of the camera and available resolution reach 16 mln pixels nowadays. Using tliis measurement technique we can obtain the quantitative information of density gradient in the flow with the high spatial resolution. This feature cause that this measurement technique can be use for investigation in turbulent flow.