Experimental study of the kinematic mixing of two fluids in a 2D enclosure

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Abstract
A simple experiment is described to investigate the buoyancy driven mixing of two fluids separated by a valve in a 2D (two-dimension) enclosure. The experiment is performed for a range of Grashof numbers, Gr ranging from 1 to 3.7×105 and a valve speed of Vval=0.05 m/s. Three distinct flow regimes are investigated within the parametric range considered, depending on the Grashof number: Chaotic (Gr⩾3.7×105), convective (1<Gr<3.7×105) and diffusive (Gr<1). A novel image processing technique is used to measure the mix fraction, interface elongation, and mixing width. The technique is based on the analysis of the color intensity of images obtained from the video recording. Mixing is quantified by analysis of the interface length and mixing width, from which the molecular mixing rate and Lyapunov exponents are deduced. The chaotic regime is found to be efficiently mixed compared with the convective and diffusive regimes.