Berkeley Fluids Seminar
University of California, Berkeley
Bring your lunch and enjoy learning about fluids!
Wednesday, May 11, 2016
240, Bechtel Hall, 13:00-14:00
Meng Wang (Mechanical Engineering, UC Berkeley)
Baroclinic Critical Layers and the Zombie Vortex Instability (ZVI) in Stratified, Rotating Shear Flows
Abstract: Without instabilities, the gas in the protoplanetary disk around a forming protostar remains in orbit rather than falling onto the protostar and completing its formation into a star. Moreover without instabilities in the fluid flow of the gas, the dust grains within the disk's gas cannot accumulate, agglomerate, and form planets. A recent study shows the existence of a new hydrodynamic instability called the Zombie Vortex Instability (ZVI), where successive generations of self-replicating vortices generated via baroclinic critical layers may fill the disk with turbulence and destabilize it. The instability is triggered by finite amplitude perturbations, including weak Kolmogorov noise, in stratified flows, rotating with angular velocity and shear.
To understand the role of baroclinic critical layers in ZVI, we analyze their structures with matched asymptotic expansions, assuming viscosity determines the magnitude and thickness of the critical layer. We verify our analytically obtained leading order inner and outer layer solutions with numerical simulations. In addition, maps of the control parameter space are presented that show two regimes where ZVI occurs, and the physics that determines the boundaries of the two regimes is interpreted. The parameter map and its underlying physics provide guidance for designing practical laboratory experiments in which ZVI could be observed.