High−precision LIF measurements of three−dimensional density perturbations

Abstract : This paper reports a novel technique of the 3D measurement of density displacements in a continuously stratified fluid, here applied to internal waves. Iso-density surfaces are marked with thin fluorescein dyed planes and illuminated with a vertical laser sheet. We have developed a technique to obtain highly accurate quantitative data from the displacement of these dye planes. The vertical distribution of luminosity across each plane is cross-correlated with a Gaussian function and subsequently interpolated, allowing for a subpixel resolution of 0.05 pixels. This method combines an appealing visualization with low-noise highly accurate quantitative measurements and has the advantage above the commonly used Schlieren and PIV methods to directly visualize the motion in a plane, to allow for the measurement of vertical velocities with high velocity gradients such as e.g. near obstacles, and gives the possibility to record also lagrangian transports. Here this method is employed to internal waves. With period-averaged measurements for several vertical equidistant planes, the 3D spatial distribution of internal wave rms amplitudes is reconstructed. As a demonstration we measure the spatial structure of internal waves emitted by a horizontally oscillating sphere in a uniformly stratified fluid.
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Evgeny V. Ermanyuk, Jan-Bert Flór, Bruno Voisin. High−precision LIF measurements of three−dimensional density perturbations. 15th International Symposium on Applications of Laser Techniques to Fluid Mechanics, Jul 2010, Lisbon, Portugal. pp.1599. ⟨hal-00583110⟩



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