Bulletin of the American Physical Society
APS March Meeting 2019
Volume 64, Number 2
Monday–Friday, March 4–8, 2019; Boston, Massachusetts
Session E29: Turbulence and Instabilities |
Hide Abstracts |
Sponsoring Units: DFD GSNP Chair: Li Xi, McMaster University Room: BCEC 162A |
Tuesday, March 5, 2019 8:00AM - 8:12AM |
E29.00001: Stability of an accelerated hydrodynamic discontinuity Daniil Ilyin, William Goddard, Sergei I. Anisimov, Snezhana Abarzhi While looking from a far field, we analyze the evolution of an accelerated discontinuity separating ideal incompressible fluids of different densities. We develop and apply a general matrix method and identify a new hydrodynamic instability that occurs when the acceleration magnitude exceeds a critical threshold value. The flow dynamics conserves mass, momentum and energy in the fluid bulk and at the interface, has potential velocity fields in the fluid bulk, and is shear-free at the interface. The interface stability is set by the interplay of inertia and buoyancy. Surface tension also stabilizes the dynamics by a distinct mechanism. The growth rate and the flow fields’ structure of the unstable dynamics depart substantially from those of other interfacial hydrodynamic instabilities, thus suggesting new opportunities for stabilization, diagnostics, and control of the interfacial dynamics. |
Tuesday, March 5, 2019 8:12AM - 8:24AM |
E29.00002: Detonation Initiation in Type Ia Supernovae Gabriel Casabona, Pritom Mozumdar, Robert Fisher Type Ia supernovae play a crucial role as standardizable candles for cosmology, but their stellar progenitors remain mysterious. Underlying this mystery is a crucial physical process: the mechanism of detonation initiation in Type Ia supernovae. Early suggestions for detonation initiation, based upon a detonation initiation mechanism originally proposed by Zel'dovich, cannot apply in the highly-turbulent conditions prevalent in major Type Ia supernova channels, in which the burning is disrupted into the distributed burning regime. We demonstrate, for the first time, using both analytic estimates and three-dimensional numerical simulations, how a carbon detonation may arise in a realistic three-dimensional turbulent electron-degenerate flow. We term this new mechanism turbulently-driven detonation. The turbulently-driven detonation initiation mechanism leads to a wider range of conditions for the onset of carbon detonation than previously thought possible, with important ramifications for SNe Ia models. |
Tuesday, March 5, 2019 8:24AM - 8:36AM |
E29.00003: A Numerical Study of the Richtmyer–Meshkov Instability in a Relativistic Fluid using Multi-Directional Riemann Solvers and High-Order WENO Schemes Jamie Townsend, László Könözsy, Karl Jenkins The present work focuses on relativistic hydrodynamic (RHD) simulations of the Richtmyer–Meshkov (RM) instability in 2D and assesses the performance of different numerical schemes. The RM instability is known to occur in various high-energy phenomena such as supernovae detonations and relativistic jets. The RHD equations are solved using the finite volume method (FVM) via a third-order TVD Runge–Kutta scheme for time integration and WENO reconstructions for spatial discretization. The effect of the imposed Riemann solver is studied via the comparative use of a Rusanov, HLL, and HLLC Riemann solver. A novel multi-directional approach has been used in which all fluxes have been computed by taking into account information propagation from all spatial directions. In particular, we investigate the linear growth-rate of the instability under a parameter space consisting of positive and negative Atwood numbers and varying shock-speed for a perfect gas. The growth-rate in the linear regime has been reported to peak in the mildly relativistic limit. We aim to shed light on the numerical influence and predictive capability of computational modelling relativistic fluids. |
Tuesday, March 5, 2019 8:36AM - 8:48AM |
E29.00004: Evaluation of the turbulence velocity skewness factor in a detonation-turbulence interaction Sarah Hussein, Frank K Lu In physical and computational studies of turbulence, the velocity skewness factor is a property of interest quantifying the development of the turbulence. Tavoularis (1978) defined the velocity skewness for fully-developed turbulence as a negative ratio of the average partial derivative of streamwise velocity with respect to the axial position, S(u,x). This definition is used in the direct numerical simualtion of homogeneous isotropic turbulence. The skewness factor, in this study, is evaluated for a turbulent fluid flow as it interacts with a detonation wave. The analysis extends the long-standing definition to include the variation of the transverse velocities in all three Cartesian spatial coordinates. The skewness components are evaluated and compared to assess significance in a detonation-turbulence interaction. |
Tuesday, March 5, 2019 8:48AM - 9:00AM |
E29.00005: Correlating ocean vertical transport and surface coherent structures Aravind Harilal Meenambika, Michael Allshouse Vertical transport in the upper ocean impacts the transport of nutrients, surface mixing, and the ocean energy budget. Observing regions of significant vertical transport has proven to be difficult since vertical velocities in the ocean are often orders of magnitude smaller than horizontal velocities. What is available, however, is HF radar and satellite altimetry, which provide ocean surface velocities. While an Eulerian analysis of this field can yield some information, Lagrangian coherent structures prove to be more robust to noisy observational data. We correlate these structures on the surface to vertical transport below the surface. In particular, we compute the finite-time Lyapunov exponent (FTLE) field from just the surface velocity and compare this with the FTLE field for a full three-dimensional analysis and the corresponding vertical subduction. These correlations are tested on a high-fidelity simulation of a sheared submesoscale flow. |
Tuesday, March 5, 2019 9:00AM - 9:12AM |
E29.00006: Vegetation-generated turbulence in combined wave-current canopy flows Jiarui Lei, Heidi Nepf Laboratory experiments are conducted in combined waves and current to measure turbulence structure and intensity in arrays of wooden cylinders, a model for submerged rigid aquatic vegetation. For dense canopies, drag leads to velocity reduction within canopy. The velocity gradient at the top of canopy generates a shear layer which results in coherent vortices traveling downstream. The canopy-scale vortices control the transport of mass and momentum and penetrate into the canopy with a length of δ_{e}. In pure current, near-bed TKE (turbulent kinetic energy) is elevated as turbulence is transported from the shear region to the bed. TKE increases as the vortices develop downstream. In combined wave-current conditions, the turbulence within canopy is mainly set by the waves as the mean current is small compared to wave velocity. The near-bed turbulence is not significantly elevated by the shear-generated vortices and can be predicted using existing empirical model of stem-generated turbulence. As the ratio of wave velocity to current speed increases, the shear layer diminishes and δ_{e}, as well as the magnitude of Reynolds stress, decreases. In pure waves, no shear layer is observed and stem-generated turbulence dominates the turbulence structure and intensity within canopy. |
Tuesday, March 5, 2019 9:12AM - 9:24AM |
E29.00007: Electron Contribution in Mirror mode Instability in Quasi-linear Regime Naila Noreen The solar wind is characterized by proton temperature anisotropies. The plasma compression generates the perpendicular anisotropy, which may lead to the mode instability for high beta situation. In the present paper the mirror mode instability is discussed in the framework of simplified and reduced quasi-linear kinetic theory, which includes the contribution of electrons. It is found that the linear growth rate associated with the electron mirror mode can be much higher than that the proton mirror mode, and the electron mirror instability operates over a range of carrying out the quasi-linear analysis, it is shown that for the proton mirror instability. However, upon carrying out the quasi-linear analysis, it is shown that for the high initial growth rate does not necessarily imply dynamical importance, since the saturated magnetic field intensity associated with electron mirror instability is extremely low and that the influence on the particle temperature is minimal. The present finding shows that under some circumstances, the dynamical consequences of a system cannot simply be estimated on the basis of the linear prediction alone and that nonlinear analysis must be taken into account. |
Tuesday, March 5, 2019 9:24AM - 9:36AM |
E29.00008: Structural and Dynamical Properties of Columnar Vortices in
Rotating Rayleigh-Bénard Convection Keqing Xia, KAI LEONG CHONG, Guang-Yu Ding We study numerically the dynamical and structural properties of columnar vortices in rotating Rayleigh-Bénard convection. Our results show that the vortices form clustered structures with a characteristic length scale when their density becomes sufficiently large. Dynamically, their motion is ballistic in short time scale and crosses over to diffusive in longer time scale. We further found that the ratio of the Brownian time scale for vortex diffusion and the relaxation time scale given by the normal stress among vortices may be the key parameter that determines the structural formation of vortices. |
Tuesday, March 5, 2019 9:36AM - 9:48AM |
E29.00009: The stabilizing effect of confinement on the Rayleigh-Taylor instability Samar Alqatari, Thomas Erik Videbæk, Irmgard Bischofberger, Anette E. Hosoi, Sidney Robert Nagel A hydrodynamic instability can develop at the interface between a denser fluid placed atop a less dense one. We investigate this Rayleigh-Taylor instability between two miscible liquids in a confined Hele-Shaw geometry. Surprisingly, we find that the typically unstable interface between the dense and less-dense liquids is stabilized below a critical confinement, set by the gap spacing of the Hele-Shaw cell. This critical confinement shows power law scaling with the difference in densities between the liquids. We also discuss the dependence of the characteristic wavelength of the instability on fluid parameters and the gap spacing. Our measured wavelength in this confined geometry deviates strongly from theoretical predictions for unconfined systems, suggesting an important effect of geometry on the onset of the instability. |
Tuesday, March 5, 2019 9:48AM - 10:00AM |
E29.00010: From Rings to Smoke: Visualizing the Breakdown of Colliding Vortex Rings Ryan McKeown, Rodolfo Ostilla Monico, Alain Jack Pumir, Michael Phillip Brenner, Shmuel Rubinstein The turbulent cascade, or the means by which the energy of a flow is conveyed from large to small scales, is governed by the interactions between vortices over many scales. In order to better understand the mechanisms that govern the close-range interactions between vortices, we experimentally examine the head-on collision of two vortex rings. By seeding the vortex rings with fluorescent dye and imaging their collision with a high-speed scanning laser sheet, we visualize the breakdown dynamics of the flow in full 3D. For weak collisions at low Reynolds numbers, the colliding rings stretch radially, develop long-wavelength perturbations, and reconnect into a tiara of secondary vortex rings. Conversely, for violent collisions at high Reynolds numbers, the rings rapidly develop short-wavelength perturbations as they stretch radially before erupting into a turbulent cloud of fine-scale vortex filaments. Initiated by these instabilities, the colliding vortices break down through various distinct processes and lead to the generation of small-scale flow structures. Thus, the close-range interactions of the colliding vortices could provide new insights into the mechanistic underpinnings of the turbulent cascade. |
Tuesday, March 5, 2019 10:00AM - 10:12AM |
E29.00011: Vortex axis tracking by iterative propagation (VATIP): analyzing three-dimensional vortex structures in viscous and viscoelastic turbulent flows Lu Zhu, Li Xi Study of turbulent vortices in DNS relies heavily on visual inspection, anecdotal observations, and intuitive arguments. Quantitative analysis is limited by the lack of computational tools for the objective detection and extraction of vortex structures. Despite much progress in the development of vortex identification criteria (which shows the vortices without distinguishing their individualities), vortex tracking requires a separate step and existing techniques only targeted quasi-linear vortices. In this study, a new tracking algorithm is proposed which propagates along the vortex axis-lines and iteratively search for new directions for growth. It is the first tracking method designed for general three-dimensional vortices. The method is tested in transient flow fields with specific vortex types as well as DNS. A new procedure is also proposed that classifies vortices into commonly-observed shapes, including quasi-streamwise vortices, hairpins, hooks, and branches, based on their axis-line topology. This new method is then applied to both viscous and viscoelastic turbulent channel flows for analyzing the distribution of vortex size, shape, and location. Introducing polymer additives suppresses vortex lift-up process and fundamentally change the vortex regeneration dynamics. |
Tuesday, March 5, 2019 10:12AM - 10:24AM |
E29.00012: Realization of Confined Turbulence Through Multiple Vortex Ring Collisions Takumi Matsuzawa, Noah P Mitchell, Stephane Perrard, William T. M. Irvine We report a method to generate a steady, localized blob of turbulence by colliding multiple vortex rings successively. Our system supplies vorticity to a turbulent region through vortex rings, which enables us to create controlled turbulent flows far from boundaries. The state of turbulence can be controlled by altering properties of the injected rings. We present spatial structures and turbulence characteristics of the blobs by varying strength, size and shape of the vortex rings. This novel method provides an ideal system to study both generation and decay of turbulence absent from any boundary effects. |
Tuesday, March 5, 2019 10:24AM - 10:36AM |
E29.00013: Numerical Analysis of Iron-Zeolite Based Emission Control Device for Two-Wheelers NAFEES AHMAD, Mehul Varshney, ANCHAL VARSHNEY, SS Alam The present work involves numerical simulation of a novel emission control device (Indian Patent Publication Number: 41/2018) for about 30 million two-wheeled vehicles running on Euro3/BS III norms without a catalytic converter across the Asia Pacific. The governing equations for turbulent fluid flow and species transport with eddy dissipation and PDF models have been solved on commercial package FLUENT^{®} to predict the behavior of oxides of nitrogen (at different engine loads) in presence of Iron-Zeolite. Substrates of Iron Zeolites with high viscous resistance provide ample residence time for adsorption of exhaust gas molecules and reduction of inorganic oxides. The findings show that the concentration of harmful oxides of Nitrogen in exhaust gases gets reduced by approximately 50% by conversion to harmless nitrogen gas. Furthermore, the geometry is optimized in a way to ensure invariance in standard speed-torque characteristics of the engine by generating negligible back pressure. The device provides an optimal business and environmental solution by controlling emissions through extremely cheap and innovative Iron-Zeolite at places where ultra-expensive Platinum/Palladium/Rhodium based catalysts are not feasible. |
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