Quantitative Measurement of Colored-Fringe Background Oriented Schlieren based on Three-Step Phase Shifting

Background Oriented Schlieren(BOS) technique can be applied for quantitative flow field diagnosis with simple experimental configurations. One of the crucials steps of BOS techniques is the extraction of image displacement vectors. The cross-correlation algorithm widely used in PIV techniques have been introduced to address the BOS extraction. However, the cross-correlation algorithm depends on interrogation windows, which usually results in low spatial resolving or unstable results. This paper proposes an improved BOS approach based on three step phase-shifting algorithm with the usage of a colored-fringe pattern as background. RGB coded carrier-fringe image is composed of three phase-shifted images. Displacement vectors are extracted by comparing the different phases between the corresponding points in three separated images. This technique avoids the problem of selecting the interrogation window. Only one image is required in this approach. An experimental setup on the measurement of hot air gun was carried out by use of our proposed method. The results demonstrate that this technique can be used for quantitative measurement in flow field.