The transport of heat, salt, and contaminants is important to measure and predict in environmental flows. For example, water quality in lakes depends on vertical transport of heat and contaminants, and the transport of heat and salt in the ocean affects the global climate. To improve the measurement and modeling of transport, molecular tagging velocimetry and thermometry (MTV&T), which has been applied successfully in other engineering flows, will be extended for use in stratified flows. The technique will be applied in a laboratory model of mixing driven by internal waves at the boundary of lakes and oceans. Specific objectives of the project are to (1) extend MTV&T to salt-stratified flow, (2) quantify turbulence and mixing generated by long waves, and (3) determine the effect of intermittent forcing on the mixing and transport.
The intellectual merit of the proposed research comes from the ability to measure the mixing and turbulence in a boundary layer generated by internal waves in more detail than previously possible; MTV&T will provide two-dimensional fields of velocity, concentration, and flux while avoiding some of the pitfalls of other techniques. The proposed laboratory experiments start with a well-studied case to verify the molecular tagging technique and then extend previous laboratory work to study other factors that are important in interpreting field measurements. Concurrent field measurements will guide the design of the laboratory experiments and test the results from the lab. The proposed work exploits PI Rehmann's experience with measurements and modeling of boundary mixing and PI Hu?s expertise in advanced flow measurement and visualization techniques.
The broader impacts include training a graduate student, conducting outreach to schools, and applying molecular tagging methods to stratified flow. The outreach uses the connections that Rehmann and Hu have established with Iowa schools and programs to broaden the participation of underrepresented groups. Also, the proposed project involves the first application of the molecular tagging method to a stratified flow of environmental importance; because previous field measurements have shown that boundary mixing can control the basin-wide vertical transport in lakes and oceans, these experiments will provide valuable information for modeling contaminant transport in the environment. Furthermore, once the proposed work demonstrates the usefulness of molecular tagging for boundary mixing, it can be used in laboratory models of many other stratified flows in the environment.
