Bulletin of the American Physical Society
65th Annual Meeting of the APS Division of Fluid Dynamics
Volume 57, Number 17
Sunday–Tuesday, November 18–20, 2012; San Diego, California
Session E12: Vortex III |
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Chair: Enrico Fonda, University of Maryland Room: 26B |
Sunday, November 18, 2012 4:45PM - 4:58PM |
E12.00001: Vortex Motion in Superfluid 4He: Reformulation in the Extrinsic Vortex Filament Coordinate Space Bhimsen Shivamoggi Vortex motion in superfluid $^4$He is considered by reformulating the Hall-Vinen equation (originally formulated in the intrinsic geometric parameter space) in the extrinsic vortex filament coordinate space which is shown to provide a useful alternative approach [1]. It provides insights into the physical implications of one aspect of the friction term, associated with the friction coefficient $\alpha$, in the Hall-Vinen notation, as well as the previous neglect of the other aspect, associated with the friction coefficient $\alpha^\prime$. A nonlinear Schrodinger equation for the propagation of nonlinear Kelvin waves on a vortex filament in a superfluid is given. The localized vortex kink solution of this equation is shown to be driven unstable by the normal fluid flow along the vortex in qualitative similarity with the Donnelly-Glaberson instability of Kelvin waves on a vortex. Though the friction term associated with $\alpha$, for very small $\alpha$, has little capacity to make significant contribution to the vortex motion in a quantitative way, it appears to be able to influence the vortex kink characteristics in a qualitative way.\\[4pt] [1] B.K. Shivamoggi: {\it Phys. Rev. B} {\bf 84}, 012506, (2011). [Preview Abstract] |
Sunday, November 18, 2012 4:58PM - 5:11PM |
E12.00002: Visualizing helium II counterflow turbulence around a cylinder Tymofiy Chagovets, Steven Van Sciver We report an experimental investigation of counterflow He II around a cylinder, thermally induced through vertical channels using an optical method of flow visualization. Previous studies using particle image velocimetry (PIV) and polymer microspheres as tracers demonstrated large scale turbulent eddies both upstream (as measured by the normal fluid flow direction) and downstream of the cylinder. An interpretation of this effect requires more detailed analysis of interaction of particles with normal fluid component and quantized vortex lines. Our recent experiments using solid hydrogen particles and the particle tracking technique (PTV) will be analyzed and results will be compared with the previous experiments. In this context, recent progress in our study of the observed large scale vortex structures in helium II counterflow will be discussed. [Preview Abstract] |
Sunday, November 18, 2012 5:11PM - 5:24PM |
E12.00003: Frozen particles as cryogenic fluid tracers: observation of Kelvin waves in superfluid helium Enrico Fonda, David P. Meichle, Nicholas T. Ouellette, Katepalli R. Sreenivasan, Daniel P. Lathrop Injecting a dilute mixture of a seed gas into a cryogenic fluid produces a mist of frozen particles. These particles can be effective tracers for studying both classical and quantum cryogenic fluids. The particles resulting from injecting a hydrogen mixture in liquid helium right above the lambda transition, subsequently allowing the fluid to cool down below that temperature, allow visualization of thermal counterflow, quantized vortices and vortex reconnection. This technique is unsuitable for detailed study of vortex dynamics below 2K. We have recently discovered a new method for producing atmospheric sub-micron particles directly into superfluid helium, allowing us to study vortices at temperatures between 1.8K and 2K. By visualizing the reconnection of long vortices populating the system in that temperature regime, we have made the first direct observations of Kelvin waves in superfluid helium and characterized a prototypical event. [Preview Abstract] |
Sunday, November 18, 2012 5:24PM - 5:37PM |
E12.00004: Experimental characterization of Kelvin waves on quantized vortices following reconnection David P. Meichle, Enrico Fonda, Nicholas T. Ouellette, Daniel P. Lathrop The superfluid state of He4 exhibits reconnection of quantized vortices. Flow visualization is made possible by injecting a dilute mixture of seed gases (or atmosphere) which freeze into sub-micron tracer particles and decorate the vortex lines. Using this technique, we have for the first time directly observed the excitation of a self-similar traveling helical perturbation to a vortex core (Kelvin wave) following a reconnection of two vortices. Detailed analysis and comparison to several semi-classical theories of vortex waves will be presented, along with other recent visual observations in superfluid He flows. [Preview Abstract] |
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