Date of Award
Doctor of Philosophy (PhD)
John P. Crimaldi
Structured stirring and mixing play a dominate role in turbulent mixing and are important processes across a wide range of applications. The mixing of two scalars that share an interface has the same topology of a single scalar problem, and therefore has dominated the literature. The mixing of two scalars separated by a third, ambient fluid has received much less attention. This topology is of particular interest in that stirring may not always increase mixing between the two scalars, and some stirring protocols may further segregate the two scalars. This topology is common in many biological, environmental, chemical, industrial, and scientific applications.
The present thesis begins by developing an experimental framework with which two scalars separated by a third ambient fluid can be studied. The technique presented, referred to herein as two-channel PLIF, simultaneously quantifies two scalar fields using a pair of independently operated single-color PLIF systems that synchronously image a common region.
The two-channel technique is used to investigate how stirring and mixing bring together initially isolated scalars in a variety of flows. Flows examined include laminar vortex shedding in the cylinder wake, plumes in grid turbulence, and low Reynolds number parallel turbulent jets. It is found that the turbulence properties and flow geometry are important in determining the effect of instantaneous processes. When the separation distance of the scalars is small compared to the largest turbulence length-scales, instantaneous mixing processes are responsible for over 80% of the coalescence between the two. Further analysis using joint probabilities of the two scalars indicates that turbulent structure brings scalar filaments near to each other in attracting regions of the flow before diffusive flux brings the two scalars into coalescence. This is the first study to show in a variety of flows that turbulent structure imparts spatial correlations on initially distant scalars.
Soltys, Michael A., "Experimental Investigations on the Role of Structure in Turbulent Mixing of Initially Isolated Scalars" (2013). Civil Engineering Graduate Theses & Dissertations. 479.