Adaptive Reconstruction Method for Axisymmetric Temperature Field Based on Light Field Background Oriented Schlieren Method

Background-oriented schlieren (BOS) is an effective noncontact temperature field reconstruction method. However, when it is used in limited near-field measurement environments, the traditional parallel light path assumption no longer holds and the location of the temperature field is hard to measured, then the adaptive measurement capability of BOS is greatly limited. Therefore, in order to expand the application scenarios of BOS to limited near-field measurement environment, a light field BOS method has been proposed in this article to improve the reconstruction accuracy of the temperature field by employing characteristic of light field camera capturing multiple directions light and fan light path model. First, the light field imaging model is combined with Zhang’s calibration method to calibrate parameters of light field camera in order to obtain the internal component distance. Second, in near-field calculation, the deviation of the rays passing through temperature field is calculated by image processing, and the center of temperature field is obtained by using rays with zero deviation. Therefore, the location of temperature field can be obtained adaptively. Finally, deflection angle is solved based on the light field BOS light path model, and then refractive index field is reconstructed using Abel inverse transformation, which in turn reconstructs temperature field. The temperature field reconstruction results has been compared with traditional parallel light path schlieren method by using the measurement values of thermocouple as standard. The experimental results show that the light field BOS reconstruction error was reduced by 2.67% at maximal 1100 K of the measured temperature field, which confirmed the feasibility of the model in limited near-field measurement environment.