Combined PIV-LIF system for measuring fluid velocities and concentrations

环境流的实验模拟为诸如污染扩散和养分输送等问题提供了重要的见解。在我们的实验室中，我们已经研究了热分层对环境流的混合和传输的稳定影响。为了分析实验，我们已经广泛使用的技术，非侵入性地揭示平均视线失真，可以测量理想化的，展向均匀流的动态。 然而，为了测量现实流动的复杂动力学，我们还需要对流体速度和浓度进行瞬时测量。 通过本提案要求的粒子成像测速和激光诱导荧光（PIV-LIF）设备组合提供了这种能力，因此将大大提高我们的研究潜力和我们将结果应用于真实的世界的能力。具体而言，该设备将用于测量大气逆温情况下污染物的扩散情况，并将研究在大气和海洋中移动的波浪的生命周期。 由于逆温时温度随高度增加，垂直运动受到抑制，混合受到抑制。 因此，污染物可能被困在逆温层之下，或者可能集中在逆温层本身。 虽然我们对均匀环境中污染物的扩散有很多了解，但目前试图将这些结果扩展到包括热分层的影响，只涉及简单的物理学。PIV-LIF系统将使我们能够扩大我们的研究，包括风的影响，以及污染物扩散的分层。 层结还允许存在“内波”，这是发生在大气层内的波动。 内波在它们破碎的地方产生晴空湍流，我们已经证明了波本身可以由湍流产生，尽管它们产生的机制仍然不清楚。 有了PIV-LIF系统，我们将首次能够同时测量湍流和它们产生的波浪的特性，从而使我们能够预测海洋混合层中湍流产生的内波的能量。

Experimental modeling of environmental flows offer critical insights into such problems as pollution dispersion and nutrient transport. In our laboratories, we have examined the stabilizing influence of thermal stratification upon mixing and transport of environmental flows. To analyze experiments, we have made extensive use of techniques that non-intrusively reveal average line-of-sight distortions and which can measure the dynamics of idealized, spanwise-uniform flows. However, to measure the complex dynamics of realistic flows, we additionally need to make instantaneous measurements of fluid velocities and concentrations. The combined Particle Imaging Velocimetry and Laser-Induced Fluorescence (PIV-LIF) equipment requested through this proposal offers exactly this capability and will therefore vastly improve our research potential and our ability to apply our results to the real world. Specifically, the equipment will be used to measure the dispersion of pollutants in the presence of an atmospheric inversion and will study the lifecycle of waves that move within the atmosphere and ocean. Because temperature increases with height at an atmospheric inversion vertical motion is inhibited and mixing suppressed. Thus pollutants can remain trapped underneath an inversion or may concentrate at the inversion itself. Although much is known about pollutant dispersion in uniform environments, attempts to extend these results to include the influence of thermal stratification presently involves only simple heuristics. The PIV-LIF system will allow us to broaden our research to include the effects of winds as well as stratification upon pollutant dispersion. Stratification also permits the existence of ``internal waves'', which are undulations occurring within the atmosphere. Internal waves create clear-air turbulence where they break and we have shown that the waves themselves can be generated by turbulence, although the mechanism for their generation remains unclear. With the PIV-LIF system we will for the first time be able to measure simultaneously the properties of the turbulence and the waves they generate thus allowing us to predict with what energy internal waves are generated by turbulence in the ocean's mixed layer.