RUI: Instability and turbulence experiments in two-dimensional flows

准二维（2D）流体流动发生在一系列环境中，包括大气和天体物理现象以及磁化聚变反应堆等离子体。 然而，准二维流动与三维流动有显著的不同，并且由于相对较少的专门的二维实验，其物理学仍然知之甚少。本研究在实验室实验中使用肥皂膜研究准二维流体动力学的基本物理，重点是基本流的稳定性以及湍流和平均流剪切之间的相互作用。 流动可以被电磁驱动，产生方形涡格，或者在圆形库埃特单元中，产生环形剪切流。 这些流动是2D中最基本的流动之一，但它们没有得到足够的实验关注。 由于在准二维系统中难以测量外阻力和内粘度，定量研究一直受到阻碍。 这些实验采用了一种新的技术来测量和区分这些影响，因此将是第一个能够定量比较理论和实验在这些和其他准二维流。 方形涡格的线性稳定性预测已经存在，并将得到检验。 初步数据显示，流动比预测的更稳定。 圆形库埃特流理论上是稳定的，但在这个实验中观察到的波动表明存在不稳定性，这将被详细研究。 进一步的实验将研究湍流和平均流剪切之间的相互作用，以阐明已知存在于大气和聚变反应堆流中的流剪切抑制湍流传输的机制。PI是在一个主要的本科院校的边缘，一个关键的过渡到一个既定的研究文化，并期望成为本科研究的典范。这项研究将有助于促进这一转变。实验室在部门的存在增强了实验室课程，并有助于招聘和留住有才华的学生和教师。

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.