Quantitative analysis of the flow field is an effective method to study hydrodynamics. As a flow field measurement technology, the\nBackground Oriented Schlieren (BOS) is widely used. However, it is difficult to measure the complex transparent flow field (flow\nfield with large refractive index gradient) using the BOS experiment. In order to overcome this difficulty and improve the accuracy\nof the BOS experiment, this paper presents a hybrid adaptive wavelet-based optical flow algorithm for the BOS. The current\nalgorithm is a combination of the traditional optical flow algorithm and the wavelet-based optical flow algorithm. By adding the\ninitial value constraints, the adaptive scale constraints, and the adaptive regularization constraints, the algorithm can effectively\novercome the above-mentioned difficulty and also improve its accuracy. To further illustrate the feasibility of the proposed\nmethod, this paper uses the simulation data, the data of the DNS datasets, and the data of the BOS experiment to verify the\nperformance of the algorithm. The experiment of comparing the proposed algorithm with the existing ones is carried out on the\nDNS datasets and the data of the BOS experiment. Finally, the proposed method is verified by a practical BOS experiment. The\nresults show that the proposed algorithm can effectively improve the measurement accuracy of displacements.
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