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New data assimilation technique for turbulent flows is proposed, which allows determination of the turbulent viscosity, velocity and pressure distributions from the experimentally measured temperature fields. Measurements are performed for a round jet of hot air using nonintrusive Background Oriented Schlieren technique. Thus, seedless velocity and pressure measurement is realized, as well as measurement of the turbulent viscosity field without usage of any particular turbulence model. Data assimilation results are shown to be in good agreement with the conventional RANS simulations using the Spalart–Allmaras and k-ɛ turbulence models, if adequate smoothing of the input temperature field is performed and sufficient regularization of the energy equation in regions with uniform temperature is provided.

New variant of Background Oriented Schlieren (BOS) technique is proposed for the measurements of strongly refracting objects. The employed pattern presents a rectangular grid of color dots. Special color encoding makes every dot unique provided its nearest neighbors can be identified. This allows robust matching of the dot images for schlieren objects with arbitrary large apparent displacements. Also, possible formation of multiple images of the same dot due to strongly nonlinear variations of the refractive index can be used to improve the accuracy of the refractive index field measurement. Multi-frame approach is employed to improve the spatial resolution. Potential of the proposed technique is demonstrated by measurements of the diffusion layers in aqueous solutions of sodium chloride and ethanol.