טכניון מכון טכנולוגי לישראל
הטכניון מכון טכנולוגי לישראל - בית הספר ללימודי מוסמכים  
Ph.D Thesis
Ph.D StudentZakharin Boris
SubjectSchlieren Systems Analysis for Investigation of Aero-
Optical Effects in Refractive Turbulent Flows
DepartmentDepartment of Aerospace Engineering
Supervisor Professor Josef Stricker


Abstract

 Several aspects of aero-optics, mainly concerned with light propagation through refractive turbulent flows, have been considered.

   Schlieren method as a technique for precise wave front measurements was investigated.  Wave optics theory of conventional schlieren was developed. The theory resolved the basic inconsistency between the wave and the geometrical optics interpretations of the method, currently existing in the literature. The imaging properties of the system were predicted. It was shown that the system has poor focusing properties.

   Schlieren systems with a coherent light source were investigated by Fourier optics technique. New cutoff filters were proposed and the imaging properties of the systems were studied. High precision of the measurements was predicted.

   The Fourier optics approach for multiple-source schlieren system was developed leading to a unified theory, which relates the focusing properties and out-of-focus noise reduction properties of the system.

    Insertion of a light source into the flow, without disturbing the flow during image acquisition, was suggested. The light source is a spark, generated by optical breakdown of high-power laser beam. The method was demonstrated experimentally. The technique was proposed for restoration of images, distorted by aero-optical aberrations. It was suggested to measure the aberrations by the schlieren technique. Incoherent imaging of a target object was considered and Wiener deconvolution filter was applied for the restoration. Computational simulation of the method was performed and successful restoration was obtained.

    An aero-optical model for electromagnetic wave propagation through an inhomogeneous turbulent medium was developed. The model uses local medium representations based on Wigner-Ville and wavelet transform spectra.