Professor Andy Bragg from Duke University will be presenting a seminar on the surprising effects of the Prandtl number on mixing in stratified turbulence, as part of the Environmental Fluid Dynamics series. His research focuses on the complex and often unpredictable motion of turbulent flows in natural and engineered systems. These flows play a critical role in various environmental phenomena, including atmospheric clouds, ocean circulation, and the broader implications of climate change. With a background in both applied mathematics and fluid dynamics, Dr. Bragg’s expertise has been shaped by postdoctoral work at Los Alamos National Laboratory and Cornell University, as well as his PhD from Newcastle University in England.

In this seminar, Dr. Bragg will explore how the mixing coefficient (MC)—the ratio of turbulent potential energy dissipation rate (TPEDR) to turbulent kinetic energy dissipation rate (TKEDR)—depends on key parameters like the Reynolds, Froude, and Prandtl numbers. Recent findings have revealed that in strongly stratified turbulent flows, changes in the Prandtl number (Pr) can significantly alter the MC. Notably, increasing the Prandtl number leads to a decrease in the TPEDR, with the MC dropping by nearly a factor of three as the Prandtl number increases from 1 to 7. Dr. Bragg will explain the physical mechanisms behind this behavior, offering new insights into the relationship between buoyancy, mixing, and turbulence in natural systems.