RUI: Instability and turbulence experiments in two-dimensional flows

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Fontana0854509Quasi-two-dimensional (2D) fluid flows occur in a range of contexts including atmospheric and astrophysical phenomena and magnetized fusion reactor plasmas. However, quasi-2D flows differ markedly from their three-dimensional counterparts, and with relatively few dedicated 2D experiments, their physics remains poorly understood. This research studies the basic physics of quasi-2D fluid dynamics in laboratory experiments using soap films, with emphasis on the stability of basic flows and the interaction between turbulence and mean flow shear. The flows may be driven electromagnetically, producing a square vortex lattice, or in a circular Couette cell, generating annular shear flow. These flows are among the most basic ones in 2D, but they have not received adequate experimental attention. Quantitative studies have been hampered by the difficulty of measuring the external drag and internal viscosity in the quasi-2D system. These experiments employ a novel technique for measuring and distinguishing these effects, and hence will be the first ones capable of a quantitative comparison between theory and experiment in these and other quasi-2D flows. Linear stability predictions for the square vortex lattice exist and will be tested. Preliminary data suggest the flow is more stable than predicted. The circular Couette flow is theoretically conjectured to be stable, but fluctuations observed in this experiment indicate the presence of an instability, which will be investigated in detail. Further experiments will examine the interaction between turbulence and mean flow shear to illuminate the mechanism of suppression of turbulent transport by flow shear known to exist in atmospheric and fusion reactor flows. The PI is at a primarily undergraduate institution at the verge of a critical transition towards an established research culture and expecting to emerge as a model for undergraduate research. This research will help to promote that transition. The presence of the laboratory in the department enhances the laboratory curriculum and helps in recruiting and retention of talented students and faculty.