Experimental environmental hydraulics: mixing in turbulent flows

长期以来，海洋一直被认为是水生废物产品的最终接收体。日益严格的环境污染法律推动了环境水力学的研究。环境水力学关注的是从烟囱到大气的污水的处置和意外溢出，以及通过排污口进入河流、湖泊和海洋等地表水体的问题。以及对流出物随后在当地或区域尺度(长达100公里)的扩散的预测。通过稀释来寻求最小化或减轻污染物的有害影响。湍流的显著特性之一是它能够极快地混合和稀释矢量(流出物速度)或标量(污染物)。在流出物和接收水体中的任一个或两者中都可能存在湍流。为了最小化或减轻污染物的影响，会产生诸如稀释区的计算等工程问题。以及意外泄漏污染物浓度和扩散程度的估计。长期研究目标是更深入地了解湍流传输和混合过程，短期目标是通过实验研究以下三个主题。1)当湍流射流被释放到湍流接收流体中时，环境湍流对射流水力和稀释的影响。这项工作将继续最近的前期工作，表明目前的假设，即射流驱动的稀释和湍流扩散可以叠加，可能会大大高估稀释率。(2)湍流中差异扩散的重要性。大多数环境流动涉及不止一个标量，处于中等雷诺数，其中差异扩散可以忽略的假设不再成立。3)在各向同性均匀湍流中，这项工作将调查射流中差异扩散的程度。(3)各向同性均匀湍流中的拉格朗日流动统计。这些统计将在使用合成射流阵列创建的流动中使用三维粒子跟踪测速仪进行实验确定。结果将用于改进环境流动的湍流扩散模型。

The ocean has long been considered as the ultimate receiving body for water-borne waste products.  The increasingly stringent environmental laws on pollution motivates the study of environmental hydraulics.  Its concern is with the disposal of and accidental spills of effluents from smoke stacks to the atmosphere and through outfalls to surface water bodies like rivers, lakes and oceans, and the prediction of the effluents' subsequent dispersion at the local or regional scale (up to 100 km).  Minimization or mitigation of the detrimental effects of the pollutants is sought though dilution.  One of the remarkable properties of turbulence is its capacity to mix and dilute either a vector (effluent velocity) or a scalar (pollutant) extremely rapidly.  Turbulence can be in either or both the effluent and the receiving water body.  Minimizing or mitigating the effects of the pollutants gives rise to engineering problems such as the calculation of dilution zones, and the estimation of pollutant concentrations and extent of spreading from accidental spills.  The long term research objective is a deeper understanding of turbulent transport and mixing processes, while the short term goals are to investigate the following three topics experimentally.  1) The effect of ambient turbulence on jet hydraulics and dilution when a turbulent jet is released into a turbulent receiving fluid.  The work will continue recent preliminary work indicating that the current assumption, that jet driven dilution and turbulent diffusion can be superimposed, may significantly over-predict dilution rates.  2) The importance of differential diffusion in turbulent flows.  Most environmental flows involve more than one scalar and are at moderate Reynolds numbers where the assumption that differential diffusion is negligible no longer holds.  The work will investigate the degree of differential diffusion in jets over a range of Reynolds numbers and in the presence of ambient turbulence.  3) Lagrangian flow statistics in isotropic homogeneous turbulence.  These will be determined experimentally using 3-D particle tracking velocimetry in a flow created using a synthetic jet array.  The results will be used to improve turbulent dispersion models of environmental flows.