Experimental environmental hydraulics: mixing in turbulent flows

长期以来，海洋一直被认为是水生废物的最终接收体。 日益严格的环境污染法规推动了环境水力学的研究。 它所关注的是烟囱排放的废水的处置和意外泄漏到大气中，以及通过排放口泄漏到河流、湖泊和海洋等地表水体，并预测这些废水随后在当地或区域范围内（最远100公里）的扩散情况。 通过稀释来寻求最小化或减轻污染物的有害影响。 湍流的一个显著特性是它能够非常迅速地混合和稀释矢量（流出速度）或标量（污染物）。 湍流可以在流出物和接收水体中的任一个或两者中。 最大限度地减少或减轻污染物的影响会引起一些工程问题，如稀释区的计算、污染物浓度的估计以及意外溢漏的扩散程度。 长期研究目标是加深对湍流输送和混合过程的理解，而短期目标是通过实验研究以下三个主题。 1)当紊流射流释放到紊流接收流体中时，环境紊流对射流水力学和稀释的影响。 这项工作将继续最近的初步工作表明，目前的假设，射流驱动的稀释和湍流扩散可以叠加，可能会显着高估稀释率。 2)紊流中微分扩散的重要性。 大多数环境流涉及一个以上的标量，并在中等雷诺数下，微分扩散可以忽略不计的假设不再成立。 这项工作将调查的程度不同的扩散射流在一定范围内的雷诺数和在环境湍流的存在。 3)各向同性均匀湍流中的拉格朗日流统计。 这些将通过使用合成射流阵列创建的流中的3-D粒子跟踪测速仪进行实验来确定。 研究结果将用于改进环境流的湍流扩散模型。

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.