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Research of background-oriented schlieren based on two-dimensional de Bruijn sequence color coding technology

Background-oriented schlieren (BOS) is a novel flow visualization technology, which has the advantages of simple device, low cost, and quantitative measurement. In this paper, a BOS technique with two-dimensional color coding background is presented, which can be referred to as color background-oriented schlieren (CBOS). Different from traditional background schlieren technique, we designed a pattern combining ‘cosine dot’ and two-dimensional color coding as the background of BOS technique. Inspired by the coding principle based on De Bruijn sequence coding in the spatial coding method of traditional structured light coding technology, the pattern of ‘cosine dot’ is generated by multiplying the fringes in two perpendicular directions. In order to integrate the intensity value of cosine dots and corresponding encoded colors into a single pattern, and to separate them completely, the HSV color model is applied to address the problem. We calculate the perturbation degree of test flow fields by searching positions of the local intensity maximum of the cosine dot patterns with and without flow fields. The function of two-dimensional color coding is employed to locate the relative position of each local intensity maximum point. Finally, we carried on the simulation experiment and the real experiment to verify the feasibility of this method.