Bulletin of the American Physical Society
APS March Meeting 2020
Volume 65, Number 1
Monday–Friday, March 2–6, 2020; Denver, Colorado
Session M20: Turbulence & Nonlinear Dynamics |
Hide Abstracts |
Sponsoring Units: DFD GSNP Chair: Joel Newbolt, Harvard University Room: 301 |
Wednesday, March 4, 2020 11:15AM - 11:27AM |
M20.00001: Propagating oscillons in a 1Dim. Faraday experiment Jose Wesfreid, Samantha Kucher, Pablo Cobelli We present the first experimental evidence of the existence of trains of propagating oscillons or localized structures in a 1D Faraday experiment in water. |
Wednesday, March 4, 2020 11:27AM - 11:39AM |
M20.00002: Linearly driven flow on a rotating sphere Rohit Supekar, Vili Heinonen, Keaton Burns, Jörn Dunkel We investigate a generalized Navier–Stokes (GNS) equation as an analytically tractable minimal model for fluid flows driven by active stresses. The GNS dynamics couple an advective nonlinearity with a generic linear instability and have been shown to permit exact solutions in a stationary 2D spherical geometry. Here, we extend the analysis to actively driven flows on rotating spheres, motivated in part by the complex flow patterns observed in planetary atmospheres. The resulting model generalizes the widely studied barotropic vorticity equation by accounting for internal forcing effects that depend on the flow vorticity itself. We find exact solutions of the GNS equations corresponding to time-independent zonal jets and their superposition with westward propagating Rossby waves. Simulations for large rotation rates confirm that the statistically stationary state is close to these exact solutions. The phase speed of the nonlinear Rossby waves measured in the simulations agrees well with analytical predictions. |
Wednesday, March 4, 2020 11:39AM - 11:51AM |
M20.00003: Numerical Simulations of Gravitational Waves from Early-Universe Turbulence Alberto Roper Pol We perform direct numerical simulations of magnetohydrodynamic turbulence in the early universe |
Wednesday, March 4, 2020 11:51AM - 12:03PM |
M20.00004: Imaging Fluorescence of He^{*}_{2} Excimers Created by Neutron Capture in Liquid He II—a New Approach for Turbulent Flow Research Xin Wen, Shiran Bao, Landen McDonald, Josh Pierce, Geoffrey L Greene, Morris Lowell Crow, Xin (Tony) Tong, Anthony Mezzacappa, Ryan Glasby, Wei Guo, Michael Fitzsimmons We show unequivocal evidence for formation of He^{*}_{2} excimers in liquid He II created by ionizing radiation produced through neutron capture. Laser beams induced fluorescence of the excimers. The fluorescence was recorded by a camera at a rate of 55.6 Hz with the ability to determine the location of an event with an uncertainty of 5 microns. The technique enables measurement of turbulence around macroscopic size (liter+) objects or vortex matter in three dimensions under conditions of extreme Reynolds number. Using thermal counterflow techniques we explored excimer flow in cryogenic He. |
Wednesday, March 4, 2020 12:03PM - 12:15PM |
M20.00005: Small-scale Energy Transfer in Turbulence James Chen, Mohamad Cheikh The dynamics behind the multi-scale energy transfer in turbulent flows is investigated by introducing morphing continuum conservation laws on the basis of the Boltzmann-Curtiss kinetic theory. The resulting conservation laws reveal the existence of small-scale routes for the flow of energy broading the view on energy cascade (forward or inverse). The comparison of the turbulence characteristic with the reference study indicates that the turbulence features in both frameworks are equivalent at the global and small-scales. The analysis reveals that at the small-scale both forward and inverse energy cascade exist in homogeneous isotropic turbulence while an overall negative energy flux (forward cascade) is present globally. |
Wednesday, March 4, 2020 12:15PM - 12:27PM |
M20.00006: Optimal perturbations for transient growth in a 3D stratified channel using nonlinear direct-adjoint looping Ritabrata Thakur, Arjun Sharma, Rama Govindarajan Laminar shear flows often transition to turbulence at Reynolds numbers smaller than that of their first linear instability. The underlying mechanism can be transient algebraic growth, either linear or nonlinear in nature. We obtain the maximum perturbation energy growth in a three-dimensional heated plane channel. A nonlinear technique of direct-adjoint-looping is employed to numerically achieve this. With this technique, we also obtain the initial velocity and temperature perturbation structure that leads to this growth. The energy growth associated with this optimal can be large enough to push the flow to turbulence. We study the effect of varying stratification strengths (gradient Richardson numbers), Reynolds numbers, and target times on the structure of the optimal. We show similarity or the lack thereof between the optimal perturbations for small (linear optimal) and large (non-linear optimal) initial energies. |
Wednesday, March 4, 2020 12:27PM - 12:39PM |
M20.00007: Role of elasticity and solvent viscosity on the center mode instability in pipe Poiseuille flow of Oldroyd-B fluids. Indresh Chaudhary, Ganesh Subramanian, Viswanathan Shankar A linear stability analysis of pipe Poiseuille flow of an Oldroyd-B fluid has been carried out to investigate the interplay among fluid inertia, elasticity and the ratio of solvent to the total viscosity. The stability has been analyzed for axisymmetric perturbations using pseudospectral and shooting methods. The system is found to be linearly unstable at the Reynolds numbers relatively lower than the values for which the transition to turbulence is typically observed for the Newtonian pipe flows. The system has been analyzed for the vast ranges of the wavelength, Reynolds number, elasticity number and the ratio of solvent to the total viscosity. In the limit of low elasticity, the fluctuations are found to be near the axis in the flow domain; hence we refer to this unstable mode as ‘centre mode’. This unstable mode stabilizes in the UCM limit (absence of solvent). Various scalings among the threshold and critical parameters have been established. Comparisons of the present results with those from the experimental studies in the existing literature have been made to establish theoretical evidence for the instability in viscoelastic flows which can potentially turn the steady laminar base flow into a turbulent one. |
Wednesday, March 4, 2020 12:39PM - 12:51PM |
M20.00008: Turbulence generation through an iterative cascade of the elliptical instability Ryan McKeown, Rodolfo Ostilla Monico, Alain Jack Pumir, Michael Phillip Brenner, Shmuel Rubinstein Turbulent flows are notoriously difficult to study due to the lack of a mechanistic framework that encapsulates how vortices interact, break down, and form new vortices, driving the cascade of energy down to the dissipative scale. We demonstrate the existence of a novel mechanism in which two counter-rotating vortices violently collide and break down, leading to the rapid development of a turbulent energy cascade mediated by iterations of the elliptical instability. We probe the full 3D dynamics of this complex breakdown by conducting both experimental flow visualizations and numerical simulations of colliding vortex rings. The onset of the elliptical instability generates an ordered array of secondary vortex filaments that are perpendicular to the original cores. Adjacent secondary filaments counter-rotate and interact with each other. In the high-Reynolds number limit, we observe another iteration of this instability, whereby even smaller tertiary filaments form in the same manner. The energy spectrum of this breakdown exhibits Kolmogorov scaling, E(k) ~ k^(-5/3), a hallmark of homogeneous isotropic turbulence. Clear evidence of this mechanism of vortex generation has also been recently observed over many length scales in recent numerical simulations of forced turbulence. |
Wednesday, March 4, 2020 12:51PM - 1:03PM |
M20.00009: 3D Visualization of Reconnections in Vortex Ring Collision Joel W. Newbolt, Ryan McKeown, Shmuel Rubinstein Vortex interactions appear in many fluid systems, from the wake behind an airplane in flight to that of a ship moving through the water. This is because friction between a fluid and a solid boundary can generate vorticity in the fluid. A simple example is the vortex ring, yet even the interaction between two vortex rings can cause instabilities that break the symmetries of the flow. When two vortex rings of equal size collide head-on at moderate Reynolds number, the rings undergo an instability that brings the two vortex cores together at several points around the circumference of the rings. As the two vortex cores touch, there is an annihilation of the opposing vorticity from each ring which results in reconnection between the original two vortex rings. These reconnections have a complicated 3D structure that is difficult to measure experimentally, leading many studies to focus on numerical simulation. By scanning a laser sheet across the collision of two dyed vortex rings, we are able to reconstruct a tomographic 3D visualization of the vortex ring collision and reconnection as it occurs. This 3D visualization allows for comparison between the structure of reconnections in experiment and the predictions from numerical models. |
Wednesday, March 4, 2020 1:03PM - 1:15PM |
M20.00010: Dynamics and deformation of a vortex during pairing under the influence of external shear Patrick Folz In general, a given vortex in a real flow may interact with other nearby vortices as well as large-scale background flows such as shear. To better understand the behavior of the vortices in such flows, the dynamics and interactions of a pair of two-dimensional like-signed viscous vortices having a circulation ratio Λ = Γ_{1}/Γ_{2} = (a^{2}_{1}/a^{2}_{2})(ω_{1}/ω_{2}) under the influence of a linear background shear having vorticity ω_{2}, of strength ζ = ω_{S}/ω_{2}, with finite viscosity, are investigated numerically. The main flow regimes, pairing and separation, are identified and briefly discussed; this work focuses on vortex-dominated pairings, in which the shear is observed to primarily aid or hinder the onset of detrainment, which precipitates the main convective interaction that results in a single final vortex. During such pairings, the vortices revolve with varying peak-peak distance b, such that the strain rate each vortex induces on the other varies in time, while the orientation of this vortex-induces strain rate relative to that of the background shear also varies. This results in a periodic deformation effect. The nature of this effect is examined and discussed. The subsequent pairing outcomes are then outlined and characterized in terms of key parameters. |
Wednesday, March 4, 2020 1:15PM - 1:27PM |
M20.00011: Transition to Condensate Formation in a Thin Rotating Fluid Layer Moritz Linkmann, Michele Buzzicotti Two-dimensional (2d) and quasi-2d flows occur at macro- and mesoscale in a |
Follow Us |
Engage
Become an APS Member |
My APS
Renew Membership |
Information for |
About APSThe American Physical Society (APS) is a non-profit membership organization working to advance the knowledge of physics. |
© 2024 American Physical Society
| All rights reserved | Terms of Use
| Contact Us
Headquarters
1 Physics Ellipse, College Park, MD 20740-3844
(301) 209-3200
Editorial Office
100 Motor Pkwy, Suite 110, Hauppauge, NY 11788
(631) 591-4000
Office of Public Affairs
529 14th St NW, Suite 1050, Washington, D.C. 20045-2001
(202) 662-8700