Holographic interferometric tomography (HIT) can provide reconstruction of instantaneous three-dimensional gross flow fields. The technique, however, encounters ill-posed reconstruction problems in practical applications. Experimental data are usually severely limited in projection and angular scanning when a field is captured instantaneously or under the obscuration of test models and test section enclosures. A reconstruction algorithm, termed the variable grid method (VGM), has been developed to improve the reconstruction under these ill-posed conditions. To test the performance of our HIT incorporated with VGM, a three-dimensional gravity-driven flow around two interacting isothermal cubes is studied experimentally. The flow can provide a challenging reconstruction problem and lend itself to accurate numerical solution for cross-comparison. The refractive index fields at two horizontal sections of the thermal plume with and without an opaque object, respectively, are reconstructed by the HIT as a function of view angle varying from the full view to 40 deg. The resulots from the HIT are then evaluated by comparing with those from numerical calculation and thermocouple thermometry. The study demonstrates that the VGM is superior to the conventional fixed grid method, especially under ill-posed conditions, and confirms that the HITis aplicable to reasonably complex, three-dimensional fluid-flow experiments.
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