Combined PIV-LIF system for measuring fluid velocities and concentrations

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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.