By Richard Mclaughlin, University of North Carolina at Chapel Hill

The behavior fluids is greatly complicated by the presence of stratification:  Bodies and jets may move ambient fluids into regions creating buoyancy forces which either are mitigated by mixing or create strong flows.  We overview some of our theoretical, computational, and experimental studies of the motion of bodies and buoyant fluids moving through a stratified background density field, focusing on the vertical transport.  Interesting critical phenomena are observed in which bodies and buoyant fluids may either escape or be trapped as parameters (such as the propagation distance) are varied.  Two models are discussed:  First, we discuss the Morton-Taylor-Turner model for which we (Camassa, McLaughlin, Tzou) have rigorously established, within this hierarchy, the optimal mixer within a broad class of ambient stratifications.  Second, we examine wall induced mixing in the evolution of passive scalar skewness in channels and ducts, joint work with Aminian, Bernardi, and Camassa.