This grant will be used to purchase index-matching fluid to operate an existing large-scale flow facility to explore flows over complex topography (relevant to aerodynamics and geophysical phenomena), within complex geometries (flow in porous media and coral reefs, turbines, etc.) and in the presence of particulates (sediment transport, nutrient transport, pollutant and aerosol dispersion, etc.). The RI-matched (RIM) flow facility will permit Illinois researchers to render complex acrylic solid models and/or particulates optically transparent when immersed in a sodium iodide solution at ~63% by weight, thereby minimizing reflections and distortion and facilitating thorough non-intrusive experimentation. Intellectual Merit - The uniqueness of this facility lies in its large size (0.45 m x 0.45 m x 2.5 m test section), allowing flow studies at relevant scales and Reynolds numbers. This funding from NSF overcomes the remainder of the funding shortfall. Doing so will prevent the team from having to pursue volume reduction that would undermine the novelty and paradigm-shifting capabilities of the large-scale facility as intended with the original MRI funding. Broader Impacts - Researchers on multiple levels (46 undergraduate and 812 graduate students, 35 postdocs and 35 visiting researchers per year anticipated amongst the research groups of the Illinois faculty on the MRI proposal) will immediately benefit from one-of-a-kind training and research experiences once the facility is operational. In particular, this unique training and education will position these researchers as the next generation of leaders in experimental fluid mechanics in both academia and industry. The facility will be run in a shared-use manner, meaning its positive impact will extend well beyond Illinois to researchers at other universities and in the private sector (in addition to the numbers listed above).
Many fluid flows, in a range of natural environments and industrial applications, move over surfaces that may be either smooth or rough, and that can range from simple to exceedingly three-dimensional and complex. Substantial research over many decades has sought to understand how turbulent flows move over these surfaces, with applications ranging from aerospace engineering to prediction of sediment movement in rivers, and from combustion chambers to fluid flow around corals. These past investigations have frequently made use of laboratory experiments, mathematical modelling and observation of real phenomena, with experimentation in the laboratory often allowing the problem to be simplified and the major controlling variables isolated and measured. However, in many laboratory investigations it has been exceedingly difficult, if not impossible, to measure the flow extremely close to the solid surface or over very complex three-dimensional topography. This is because these surfaces reflect light, which can thus impair optical measurements, or may be impossible to illuminate if very complex. This research is developing a unique laboratory facility to address this issue, in establishing an experimental channel in which the refractive index of the fluid can be matched precisely to that of the acrylic model being investigated (for instance, sediment grains, a model sand dune or turbine blade). In this way the solid is rendered ‘invisible’ by precise refractive-index matching, and permits laser light to be introduced near very complex surfaces, thus allowing optical imaging and measurement very close to these surfaces. This new laboratory channel is enabling a wide range of research within engineering and geophysical flows, with sodium iodide being used as the working fluid since it can be index-matched with acrylic and is a low-toxicity substance with which to experiment. Development of this facility and the purchase of the fluid were enabled by a separate NSF grant. However, during the project development phase, the Fukushima nuclear disaster following the Tohoku earthquake and subsequent tsunami on 11 March 2011, caused the global price of sodium iodide solution to skyrocket, making it impossible for us to purchase the amount of sodium iodide required. Subsequent to this event, we modified our experimental design to reduce the amount of sodium iodide required to fill the channel, but the design still required additional funding to purchase the fluid. This grant provided this supplemental funding that permitted the extra fluid to be purchased and thus enabled full completion of the development of this facility, which is now operational. This project has established a uniquely flexible research facility that is currently being used to investigate flow over damaged turbine blades, fluid motion over groups of desert sand dunes, and flow over and within porous surfaces that is relevant for study of pollutant and nutrient transport in gravel-bed rivers. In addition, this laboratory facility is enabling training of undergraduate and graduate students, as well as postdoctoral researchers, in a new generation of fluid mechanics measurements that will enable them to tackle key new problems of technological, environmental and societal relevance.
