Bulletin of the American Physical Society
67th Annual Meeting of the APS Division of Fluid Dynamics
Volume 59, Number 20
Sunday–Tuesday, November 23–25, 2014; San Francisco, California
Session M32: Nonlinear Dynamics V |
Hide Abstracts |
Chair: Laurette S. Tuckerman, ESPCI ParisTech Room: 2020 |
Tuesday, November 25, 2014 8:00AM - 8:13AM |
M32.00001: Burgers Turbulence on a Fractal Fourier set Michele Buzzicotti, Luca Biferale, Uriel Frisch, Samriddhi Ray We present a systematic investigation of the effects introduced by a fractal decimation in Fourier space on stochastically forced one-dimensional Burgers equations. The aim is to understand the statistical robustness of the shock singularity under different reductions of the number of the degrees of freedom. We perform a series of direct numerical simulations by using a pseudo-spectral code with resolution up to 16384 points and for various dimensions of the fractal set of Fourier modes D$_F$ \textless 1. We present results concerning the scaling properties of statistical measures in real space and the probability distribution functions of local and non-local triads in Fourier space. [Preview Abstract] |
Tuesday, November 25, 2014 8:13AM - 8:26AM |
M32.00002: Neurophysiology of pipe flow Dwight Barkley This work explores the connection between the transition to turbulence in pipe flow and the dynamics of excitable media, as exemplified by nerve cells. The primary goal is to leverage years of extensive analysis of neural systems to understand the dynamics of transitional turbulence. To demonstrate the predictive nature of the approach, model simulations will be presented for puffs in pipe flow for cases not previously studied experimentally. [Preview Abstract] |
Tuesday, November 25, 2014 8:26AM - 8:39AM |
M32.00003: The Self-Sustaining Process for Taylor-vortex flow Laurette Tuckerman, Tommy Dessup, Dwight Barkley, Jose Eduardo Wesfreid, Ashley Willis The Self-Sustaining Process (SSP) of Waleffe, like Hall's Vortex-Wave Interaction theory, was proposed as the fundamental element of turbulence in low Reynolds number turbulence in wall-bounded shear flows and consists of three phases. (i) Streamwise vortices bend nd the streamwise velocity contours via advection. (ii) The undulating streamwise velocity leads to waviness in the vortices via Kelvin-Helmholtz instability. (iii) Nonlinear interaction of the wavy streamwise vortices promotes the streamwise vortices. We explore the SSP for Taylor-vortex flow, for which streamwise (azimuthal) and wavy vortices are genuine steady states resulting from linear instabilities with well-defined thresholds. In particular, we determine the circumstances under which wavy vortices reinforce Taylor vortices. [Preview Abstract] |
Tuesday, November 25, 2014 8:39AM - 8:52AM |
M32.00004: The onset of turbulence in a square duct flow Gregoire Lemoult, Bjorn Hof Wall bounded shear flows experience a sudden transition from a laminar state to turbulence as Reynolds number, $Re$, increases. K. Avila \textit{et al.} (Science 333, 2011) recently characterized the onset of turbulence in pipe flow. They measured the probability for a localized disturbance to decay or spread and defined the critical Reynolds number, $Re_{\mathrm{c}}$, where the characteristic time for both process is equal. Using the same methodology, we measure these probabilities, decay and splitting, as a function of $Re$ in a 1200 $D$ long square duct, where $D$ is the width of the duct. We found the expected exponential probability distribution for both processes which underlines their memoryless character. From the characteristic time of these distributions, we estimate the point where turbulence first becomes sustained in a square duct flow. The main difference with pipe flow is that the characteristic time at $Re_{\mathrm{c}}$ is shorter making it more suitable for measurements of critical exponents in the framework of phase transition. These results also emphasize the universal behavior of the transition to turbulence in wall bounded shear flows. [Preview Abstract] |
Tuesday, November 25, 2014 8:52AM - 9:05AM |
M32.00005: Direct laminar-turbulent transition in Taylor-Couette flow: Experiments and simulations Christopher J. Crowley, Michael Krygier, Samuel G. Raben, Daniel Borrero, Roman O. Grigoriev, Michael F. Schatz The transition to turbulence in Taylor-Couette flow is frequently mediated by stable flow states (e.g. interpenetrating spirals). We describe a direct laminar-turbulent transition in a system with counterrotating cylinders and small aspect ratio of 5.26. In experiments probed using tomographic PIV and direct numerical simulations with realistic boundary conditions, we find the transition is hysteretic, yet highly reproducible with turbulence triggered by the growth of weak spiral flows. [Preview Abstract] |
Tuesday, November 25, 2014 9:05AM - 9:18AM |
M32.00006: Fiber bundles and geometric phases of turbulent pipe flows Francesco Fedele In this talk, I will discuss the role of continuous translation symmetries in the dynamics of turbulent pipe flows. Drawing from differential geometry, the geometric structure of the N-dimensional state space V of the Navier Stokes pipe flow can be defined by means of a base manifold P of dimension N-1 (quotient space) and 1-D fibers attached to any point p of P (fiber bundle). In V, a trajectory can be observed in a special comoving frame, from which the motion is locally transversal to the fibers (horizontal transport). The proper shift along the fibers to bring the motion in the comoving frame is called dynamical phase. This is, for example, the translational shift induced by the constant speed of a traveling wave (TW), or relative fixed point. A TW in state space projects to a fixed point on the base manifold P, whereas a relative periodic orbit (RPO) reduces to a periodic orbit (PO). In this case, the shift along the fibers includes also a geometric phase, induced by curvature of the base manifold P. As an application, I will present results on symmetry reduction of experimental pipe flow data acquired by means of Laser Induced Fluorescence (LIF) techniques exploiting a generalization of Hopf fibrations and complex projective spaces. A chaotic Lorenz-type dynamics is unveiled in the desymmetrized state space. Moreover, the analysis reveals that the time-varying speed of a turbulent peak during bursts is related to the geometric phase associated with the motion in the fiber bundle. [Preview Abstract] |
Tuesday, November 25, 2014 9:18AM - 9:31AM |
M32.00007: Streamwise-Localized Solutions with natural 1-fold symmetry Sebastian Altmeyer, Ashley Willis, Bj\"orn Hof It has been proposed in recent years that turbulence is organized around unstable invariant solutions, which provide the building blocks of the chaotic dynamics. In direct numerical simulations of pipe flow we show that when imposing a minimal symmetry constraint (reflection in an axial plane only) the formation of turbulence can indeed be explained by dynamical systems concepts. The hypersurface separating laminar from turbulent motion, the edge of turbulence, is spanned by the stable manifolds of an exact invariant solution, a periodic orbit of a spatially localized structure. The turbulent states themselves (turbulent puffs in this case) are shown to arise in a bifurcation sequence from a related localized solution (the upper branch orbit). The rather complex bifurcation sequence involves secondary Hopf bifurcations, frequency locking and a period doubling cascade until eventually turbulent puffs arise. In addition we report preliminary results of the transition sequence for pipe flow without symmetry constraints. [Preview Abstract] |
Tuesday, November 25, 2014 9:31AM - 9:44AM |
M32.00008: Kolmogorov-like Flow: Effect of the Boundaries on Stability and Transition to Weak Turbulence Ravi Kumar Pallantla, Balachandra Suri, Jeffrey Tithof, Schatz Michael, Roman Grigoriev The dynamical description of turbulence in fluid flows using non-chaotic unstable solutions of the Navier-Stokes equation, called Exact Coherent Structures (ECS), is a promising approach to understand and control the turbulence. However, it has never been properly validated in experiment. This talk discusses a quasi-two-dimensional implementation of the Kolmogorov flow that enables validation of both dynamical and statistical aspects of the ECS-based description of weak turbulence. We use a numerical model of an experiment, which employs an electromagnetically-driven thin layer of electrolyte supported by a thin layer of a liquid dielectric, to describe the effects of the boundary conditions and the system size on the stability of the base flow as well as the properties of ECS which emerge in the turbulent regime. [Preview Abstract] |
Tuesday, November 25, 2014 9:44AM - 9:57AM |
M32.00009: Search for Exact Coherent Structures in a Quasi-Two-Dimensional Kolmogorov-Like Flow Balachandra Suri, Jeffrey Tithof, Ravi Kumar Pallantla, Roman Grigoriev, Schatz Michael Recent theoretical advances suggest that turbulence can be characterized using unstable solutions of the Navier-Stokes equations having regular temporal behavior, called Exact Coherent Structures (ECS). Due to their experimental accessibility and theoretical tractability two-dimensional flows provide an ideal setting for the exploration of turbulence from a dynamical systems perspective. In our talk, we present a combined numerical and experimental study of electromagnetically driven flows in a shallow layer of electrolyte. On the numerical front we present our research concerning the search for ECS in a two-dimensional Kolmogorov-like flow. We discuss the change in the dynamics of the flow as the Reynolds number is varied. For a weakly turbulent flow, we show that the turbulent trajectory explores a region of state space which contains a number of ECS, including equilibria and periodic orbit solutions. We then discuss the occurrence of states similar to these numerically computed ECS in an experimental quasi-two-dimensional Kolmogorov-like flow. [Preview Abstract] |
Tuesday, November 25, 2014 9:57AM - 10:10AM |
M32.00010: ABSTRACT WITHDRAWN |
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