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Nontrivial topology of the Alfvén continuum and topological origin of reversed-shear Alfvén eigenmodesSep 17 2019In an inhomogeneous plasma, the ideal magnetohydrodynamics model gives rise to the Alfv\'{e}n continuum, consisting of non-square-integrable improper eigenfunctions. For a gravitating slab, we calculate a Chern number for the Alfv\'{e}n continuum on a ... More

Nontrivial topology of the Alfvén continuum and topological character of reversed-shear Alfvén eigenmodesSep 17 2019Sep 18 2019In an inhomogeneous plasma, the ideal magnetohydrodynamics model gives rise to the Alfv\'{e}n continuum, consisting of non-square-integrable improper eigenfunctions. For a gravitating slab, we calculate a Chern number for the Alfv\'{e}n continuum on a ... More

Simple Model for Estimation of the Influence of Velocity on Advancing Dynamic Contact AnglesSep 17 2019Given the importance of dynamic contact angle, its numerous applications and the complexity and difficulty of use of available approaches, here we present a new simple semi-empirical models for estimation of dynamic contact angle's dependence on the wetting ... More

On the Physical Interpretation of Proper Orthogonal Decomposition and Dynamic Mode Decomposition for Liquid InjectionSep 17 2019The modal decomposition techniques of proper orthogonal decomposition (POD) and dynamic mode decomposition (DMD) have become a common method for analysing the spatio-temporal coherence of dynamical systems. In particular, these techniques are of interest ... More

Fully 3D Rayleigh-Taylor Instability in a Boussinesq FluidSep 17 2019Rayleigh-Taylor instability occurs when a heavier fluid overlies a lighter fluid, and the two seek to exchange positions under the effect of gravity. We present linearized theory for arbitrary 3D initial disturbances that grow in time, and calculate the ... More

Towards Unsupervised Segmentation of Extreme Weather EventsSep 16 2019Extreme weather is one of the main mechanisms through which climate change will directly impact human society. Coping with such change as a global community requires markedly improved understanding of how global warming drives extreme weather events. ... More

Direct numerical simulation of dense bubbly flows using an improved immersed boundary methodSep 16 2019Fully resolved simulation of flows with bubbles or buoyant particles is a challenging problem due to the fact that bubbles or buoyant particles are lighter than the surrounding fluid and as a result, two phases are strongly coupled together which means ... More

Nonlinear response of wrinkled premixed flames to time- and space-dependent forcing and stretchSep 16 2019Premixed-flame wrinkling is studied via a Michelson-Sivashinsky (MS) type of evolution equation retaining the Darrieus-Landau (DL) instability, a curvature effect and a geometric nonlinearity. Here it also keeps forcing by longitudinal shearflow and wrinkle ... More

Search and rescue at sea aided by hidden flow structuresSep 16 2019Every year hundreds of people die at sea because of vessel and airplane accidents. A key challenge in reducing the number of these fatalities is to make Search and Rescue (SAR) algorithms more efficient. Here we address this challenge by uncovering hidden ... More

Droplet leaping governs microstructured surface wettingSep 16 2019Microstructured surfaces that control the direction of liquid transport are not only ubiquitous in nature, but they are also central to technological processes such as fog/water harvesting, oil-water separation, and surface lubrication. However, a fundamental ... More

Higher order homogenized boundary conditions for flows over rough and porous surfacesSep 16 2019We derive a homogenized macroscopic model for fluid flows over ordered homogeneous porous surfaces. The unconfined free-flow is described by the Navier-Stokes equation, and the Darcy equation governs the seepage flow within the porous domain. Boundary ... More

Freezing a rivuletSep 16 2019We investigate experimentally the formation of the particular ice structure obtained when a capillary trickle of water flows on a cold substrate. We show that after a few minutes the water ends up flowing on a tiny ice wall whose shape is permanent. We ... More

Particle reconstruction of volumetric particle image velocimetry with strategy of machine learningSep 16 2019Three-dimensional particle reconstruction with limited two-dimensional projects is an underdetermined inverse problem that the exact solution is often difficulty to be obtained. In general, approximate solutions can be obtained by optimization methods. ... More

Lattice Boltzmann model for weakly compressible flowsSep 15 2019We present an energy conserving lattice Boltzmann model based on a crystallographic lattice for simulation of weakly compressible flows. The theoretical requirements and the methodology to construct such a model are discussed. We demonstrate that the ... More

Spectral/hp element simulation of flow past a Formula One front wing: validation against experimentsSep 15 2019Emerging commercial and academic tools are regularly being applied to the design of road and race cars, but there currently are no well-established benchmark cases to study the aerodynamics of race car wings in ground effect. In this paper we propose ... More

Interfacial flows in sessile evaporating droplets of mineral waterSep 14 2019Liquid flow in sessile evaporating droplets of ultrapure water typically results from two main contributions: a capillary flow pushing the liquid towards the contact line from the bulk and a thermal Marangoni flow pulling the drop free surface towards ... More

Uncertainty Quantification in density estimation from Background Oriented Schlieren (BOS) measurementsSep 14 2019We present an uncertainty quantification methodology for density estimation from Background Oriented Schlieren (BOS) measurements, in order to provide local, instantaneous, a-posteriori uncertainty bounds on each density measurement in the field of view. ... More

A scalable computational platform for particulate Stokes suspensionsSep 14 2019We describe a computational framework for simulating suspensions of rigid particles in Newtonian Stokes flow. One central building block is a collision-resolution algorithm that overcomes the numerical constraints arising from particle collisions. This ... More

Lifetime of a Charged Droplet Levitated in an Electrodynamic balanceSep 14 2019We report here, the time-lapse of the breakup phenomenon of a charged droplet levitated in an electrodynamic (ED) balance. During the breakup process, a levitated charged droplet undergoes evaporation leading to a reduction in droplet size and increase ... More

Resolvent analysis of compressible laminar and turbulent cavity flowsSep 13 2019The present work demonstrates the use of resolvent analysis to obtain physical insights for open-cavity flows. Resolvent analysis identifies the flow response to harmonic forcing, given a steady base state, in terms of the response and forcing modes and ... More

On the Holway-Weiss Debate: Convergence of the Grad-Moment-Expansion in Kinetic Gas TheorySep 13 2019Moment expansions are used as model reduction technique in kinetic gas theory to approximate the Boltzmann equation. Rarefied gas models based on so-called moment equations became increasingly popular recently. However, in a seminal paper by Holway [Phys. ... More

On the Wiener-Khinchin transform of functions that behave as approximate power-laws. Applications to fluid turbulenceSep 13 2019As we all know, the Fourier transform is continuous in the weak sense of tempered distribution; this ensures the weak stability of Fourier pairs. This article investigates a stronger form of stability of the pair of homogeneous profiles $(|x|^{-\alpha}, ... More

Inlet swirl decay and mixing in a laminar micropipe flow with wall slipSep 13 2019In this work, the laminar decaying inlet swirl flow in a straight micro-pipe with wall slip is solved analytically and the solution verified numerically. Based on a fully developed parabolic axial velocity profiles, the swirl velocity equation is solved ... More

Inlet swirl decay and mixing in a laminar micropipe flow with wall slipSep 13 2019Sep 16 2019In this work, the laminar decaying inlet swirl flow in a straight micro-pipe with wall slip is solved analytically and the solution verified numerically. Based on a fully developed parabolic axial velocity profiles, the swirl velocity equation is solved ... More

Mechanisms of a Convolutional Neural Network for Learning Three-dimensional Unsteady Wake FlowSep 13 2019Convolutional neural networks (CNNs) have recently been applied to predict or model fluid dynamics. However, mechanisms of CNNs for learning fluid dynamics are still not well understood, while such understanding is highly necessary to optimize the network ... More

Spline-based Interface Modeling and Optimization (SIMO) for Surface Tension and Contact Angle MeasurementsSep 12 2019Surface tension and contact angle measurements are fundamental characterization techniques relevant to thermal and fluidic applications. Drop shape analysis techniques for the measurement of interfacial tension are powerful, versatile and flexible. Here ... More

Interaction and coalescence of large bubbles rising in a thin gapSep 12 2019We present accurate measurements of the relative motion and deformation of two large bubbles released consecutively in a quiescent liquid confined in a thin-gap cell. Though the second bubble injected is smaller, we observed that in all cases it accelerates ... More

Sheared free-surface flow over three-dimensional obstructions of finite amplitudeSep 12 2019When shallow water flows over uneven bathymetry, the water surface is modulated. This type of problem has been revisited numerous times since it was first studied by Lord Kelvin in 1886. Our study analytically examines currents whose unperturbed velocity ... More

An Efficient High-Order Gas-Kinetic Scheme (I): Euler equationsSep 12 2019In this paper, an efficient high-order gas-kinetic scheme (EHGKS) is proposed to solve the Euler equations for compressible flows. We re-investigate the underlying mechanism of the high-order gas-kinetic scheme (HGKS) and find a new strategy to improve ... More

Wall turbulence without modal instability of the streaksSep 12 2019Despite the nonlinear nature of wall turbulence, there is evidence that the mechanism underlying the energy transfer from the mean flow to the turbulent fluctuations can be ascribed to linear processes. One of the most acclaimed linear instabilities for ... More

Hessian-based Lagrangian closure theory for passive scalar turbulenceSep 12 2019Self-consistent closure theory for passive-scalar turbulence has been developed on the basis of the Hessian of the scalar field. As a primitive indicator of local scalar structures, we employ Hessian into the core of the closure theory to properly characterize ... More

Feedback control for transition suppression in direct numerical simulations of channel flowSep 12 2019For channel flow at subcritical Reynolds numbers ($Re<5772$), a laminar-to-turbulent transition can emerge due to a large transient amplification in the kinetic energy of small perturbations, resulting in an increase in drag at the walls. The objectives ... More

An Extension of the Athena++ Framework for General Equations of StateSep 11 2019We present modifications to the Athena++ framework to enable use of general equations of state (EOS). Part of our motivation for doing so is to model transient astrophysics phenomena, as these types of events are often not well approximated by an ideal ... More

Structure formation in turbulence as instability of effective quantum plasmaSep 11 2019Structure formation in turbulence is effectively an instability of "plasma" formed by fluctuations serving as particles. These "particles" are quantumlike; namely, their wavelengths are non-negligible compared to the sizes of background coherent structures. ... More

Pore-Scale Flow Characterization of Polymer Solutions in Microfluidic Porous MediaSep 11 2019Polymer solutions are frequently used in enhanced oil recovery and groundwater remediation to improve the recovery of trapped non-aqueous fluids. However, applications are limited by an incomplete understanding of the flow in porous media. The tortuous ... More

Unified gas-kinetic simulation for the system of multiscale radiation hydrodynamicsSep 11 2019This paper aims at the simulation of multiple scale physics in the system of radiation hydrodynamics. The system couples the fluid dynamic evolution equations with the radiative heat transfer. The coupled system is solved by the gas-kinetic scheme (GKS) ... More

New bounds on the vertical heat transport for Bénard-Marangoni convection at infinite Prandtl numberSep 11 2019We prove a new rigorous upper bound on the vertical heat transport for B\'enard-Marangoni convection of a two- or three-dimensional fluid layer with infinite Prandtl number. Precisely, for Marangoni number $Ma \gg 1$ the Nusselt number $Nu$ is bounded ... More

On unified preserving properties of kinetic schemesSep 11 2019Numerical modeling of fluid flows based on kinetic equations provides an alternative approach for the description of complex flows simulations, and a number of kinetic methods have been developed from different points of view. A particular challenge for ... More

On unified preserving properties of kinetic schemesSep 11 2019Sep 12 2019Numerical modeling of fluid flows based on kinetic equations provides an alternative approach for the description of complex flows simulations, and a number of kinetic methods have been developed from different points of view. A particular challenge for ... More

Fractional hyperviscosity induced growth of bottlenecks in energy spectrum of Burgers equation solutionsSep 11 2019Energy spectrum of turbulent fluids exhibit a bump at an intermediate wavenumber, between the inertial and the dissipation range. This bump is called bottleneck. Such bottlenecks are also seen in the energy spectrum of the solutions of hyperviscous Burgers ... More

Shadowing the rotating annulus. Part II: Gradient descent in the perfect model scenarioSep 11 2019Shadowing trajectories are model trajectories consistent with a sequence of observations of a system, given a distribution of observational noise. The existence of such trajectories is a desirable property of any forecast model. Gradient descent of indeterminism ... More

Feedback control of vortex shedding using a resolvent-based modelling approachSep 11 2019An investigation of optimal feedback controllers' performance and robustness is carried out for vortex shedding behind a 2D cylinder at low Reynolds numbers. To facilitate controller design, we present an efficient modelling approach in which we utilise ... More

An Energy-Stable Scheme for Incompressible Navier-Stokes Equations with Periodically Updated Coefficient MatrixSep 11 2019We present an energy-stable scheme for simulating the incompressible Navier-Stokes equations based on the generalized Positive Auxiliary Variable (gPAV) framework. In the gPAV-reformulated system the original nonlinear term is replaced by a linear term ... More

On the formation of three-dimensional flows over finite-aspect-ratio wings under tip effectsSep 10 2019We perform DNS of flow over finite-aspect-ratio NACA 0015 wings to characterize the tip effects on the wake dynamics. This study focuses on the development of three-dimensional separated flow over the wing, and discuss flow structures formed on the wing ... More

Inviscid limit of vorticity distributions in Yudovich classSep 10 2019We prove that given initial data $\omega_0\in L^\infty(\mathbb{T}^2)$, forcing $g\in L^\infty(0,T; L^\infty(\mathbb{T}^2))$, and any $T>0$, the solutions $u^\nu$ of Navier-Stokes converge strongly in $L^\infty(0,T;W^{1,p}(\mathbb{T}^2))$ for any $p\in ... More

Particle Size Effects in Flow-Stabilized SolidsSep 10 2019Flow-stabilized solids are a class of fragile matter that forms when a dense suspension of colloids accumulates against a semi-permeable barrier, for flow rates above a critical value. In order to probe the effect of particle size on the formation of ... More

Nonlinear dynamics of forced baroclinic critical layersSep 10 2019In this paper, we study the forcing of baroclinic critical levels, which arise in stratified fluids with horizontal shear flow along the surfaces where the phase speed of a wave relative to the mean flow matches a natural internal wavespeed. Linear theory ... More

Elements of resolvent methods in fluid mechanics: notes for an introductory short courseSep 10 2019This is a collection of notes for part of a short course on modal methods in fluid mechanics held at DAMTP, University of Cambridge, in the summer of 2019. These notes introduce the reader to resolvent analysis as it is currently used in fluid mechanics. ... More

Topology and morphology of self-deforming active shellsSep 10 2019We present a generic framework for modelling three-dimensional deformable shells of active matter that captures the orientational dynamics of the active particles and hydrodynamic interactions on the shell and with the surrounding environment. We find ... More

Effects of rotation on the bulk turbulent convectionSep 10 2019We study rotating homogeneous turbulent convection forced by a mean vertical temperature gradient by means of direct numerical simulations (DNS) in the Boussinesq approximation in a rotating frame. In the absence of rotationour results are in agreement ... More

Nonlinear wave interaction in coastal and open seas -- deterministic and stochastic theorySep 10 2019We review the theory of wave interaction in finite and infinite depth. Both of these strands of water-wave research begin with the deterministic governing equations for water waves, from which simplified equations can be derived to model situations of ... More

Transport properties of Keplerian flows in extended local domains with no imposed fieldSep 10 2019We compare transport statistics of elongated incompressible shearing boxes for different Reynolds and magnetic Prandtl numbers, $Re$ and $Pm$, and aspect ratios, $L_z/L_x$. We find that at fixed aspect ratio $L_z/L_x=4$ and $Re = 10,000$, the turbulent ... More

Viscoelasticity-induced pulsatile motion of 2D roll cell in laminar wall-bounded shear flowSep 10 2019For the clarification of the routes to elasto-inertial turbulence (EIT), it is essential to understand how viscoelasticity modulates coherent flow structures including the longitudinal vortices. We focused on a rotating plane Couette flow that provides ... More

Mapping micron-scale wetting properties of superhydrophobic surfacesSep 10 2019There is a huge interest in developing super-repellent surfaces for anti-fouling and heat transfer applications. To characterize the wetting properties of such surfaces, the most common approach is to place a millimetric-sized droplet and measure its ... More

Viscoelastic effect on steady wavy roll cells in wall-bounded shear flowSep 10 2019An alternative step in understanding the flows of near wall drag-reducing turbulence can be examining the flow in a well-organized streamwise vortex with a laminar background. Herein, we studied the flow behaviors of the Giesekus viscoelastic fluid in ... More

DNS of Taylor-Couette flow between counter-rotating cylinders at small radius ratioSep 10 2019A counter-rotating Taylor-Couette flow with relatively small radius ratios of $\eta$ = 0.2--0.5 was investigated over a wide range of the Reynolds number, from laminar to turbulent regime, by means of three-dimensional direct numerical simulations. We ... More

Central Moment Lattice Boltzmann Method using a Pressure-based Formulation for Multiphase Flows at High Density Ratios and including Effects of Surface Tension and Marangoni StressesSep 09 2019Simulation of multiphase flows require coupled capturing or tracking of the interfaces in conjunction with the solution of fluid motion often occurring at multiple scales. We will present unified cascaded LB methods based on central moments for the solution ... More

The Kinematics of Lagrangian Flow Separation in External AerodynamicsSep 09 2019Kinematic aspects of flow separation in external aerodynamics are investigated in the Lagrangian frame. Specifically, the initial motion of upwelling fluid material from the wall is related to the long-term attracting manifolds in the flow field. While ... More

Drag reduction in boiling Taylor-Couette turbulenceSep 09 2019We create a highly controlled lab environment-accessible to both global and local monitoring-to analyse turbulent boiling flows and in particular their shear stress in a statistically stationary state. Namely, by precisely monitoring the drag of strongly ... More

On Secondary Tones Arising in Trailing-Edge Noise at Moderate Reynolds NumbersSep 09 2019Direct numerical simulations are carried out to investigate the flow features responsible for secondary tones arising in trailing-edge noise at moderate Reynolds numbers. Simulations are performed for a NACA 0012 airfoil at freestream Mach numbers 0.1, ... More

On Secondary Tones Arising in Trailing-Edge Noise at Moderate Reynolds NumbersSep 09 2019Sep 10 2019Direct numerical simulations are carried out to investigate the flow features responsible for secondary tones arising in trailing-edge noise at moderate Reynolds numbers. Simulations are performed for a NACA 0012 airfoil at freestream Mach numbers 0.1, ... More

Small scale reconstruction in three-dimensional Kolmogorov flows using four-dimensional variational data assimilationSep 09 2019We apply the four dimensional variational method to reconstruct the small scales of three-dimensional turbulent velocity fields with a moderate Reynolds number, given a time sequence of measurement data on a coarse set of grid points. The results show ... More

Phoretic Active MatterSep 09 2019These notes are an account of a series of lectures given at the Les Houches Summer School ``Active Matter and Non-equilibrium Statistical Physics'' during August and September 2018. The lectures can be viewed online at [http://www.ds.mpg.de/lmp/lectures/les-houches-2018]. ... More

Recasting Navier-Stokes EquationsSep 09 2019Classical Navier-Stokes equations fail to describe some flows in both the compressible and incompressible configurations. In this article, we propose a new methodology based on transforming the fluid mass velocity vector field to obtain a new class of ... More

Semi-analytic velocity profile for a Bingham fluid in a curved channelSep 09 2019We derive an expression for the velocity profile of a pressure-driven yield-stress Bingham fluid flowing around a 2D concentric annulus. The formula requires the numerical solution of a nonlinear equation for the positions of the yield surfaces. The results ... More

Eigenvectors, Circulation and Linear Instabilities for Planetary Science in 3 Dimensions (ECLIPS3D)Sep 09 2019Context. The study of linear waves and instabilities is necessary to understand the physical evolution of an atmosphere, and can provide physical interpretation of the complex flows found in simulations performed using Global Circulation Models (GCM). ... More

The effective shear and dilatational viscosity of a particle-laden interface in the dilute limitSep 09 2019The effective dilatational and shear viscosities of a particle-laden fluid interface are computed in the dilute limit under the assumption of an asymptotically vanishing viscosity ratio between both fluids. Spherical particles with a given contact angle ... More

On Two-Dimensional Steady Hypersonic-Limit Euler Flows Passing Ramps and Radon Measure Solutions of Compressible Euler EquationsSep 09 2019We proposed rigorous definitions of Radon measure solutions for boundary value problems of steady compressible Euler equations which modeling hypersonic-limit inviscid flows passing two-dimensional ramps, and their interactions with still gas and pressureless ... More

Neural Network Models for the Anisotropic Reynolds Stress Tensor in Turbulent Channel FlowSep 09 2019Reynolds-averaged Navier-Stokes (RANS) equations are presently one of the most popular models for simulating turbulence. Performing RANS simulation requires additional modeling for the anisotropic Reynolds stress tensor, but traditional Reynolds stress ... More

Nonlinear dynamics of acoustic bubbles excited by their pressure dependent subharmonic resonance frequency: oversaturation and enhancement of the subharmonic signalSep 09 2019The acoustic bubble is an example of a highly nonlinear system which is the building block of several applications and phenomena ranging from underwater acoustics to sonochemistry and medicine. Nonlinear behavior of bubbles, and most importantly 1/2 order ... More

A Framework for Data-Based Turbulent Combustion Closure: A Posteriori ValidationSep 08 2019In this work, we demonstrate a framework for developing closure models in turbulent combustion using experimental multi-scalar measurements. The framework is based on the construction of conditional means and joint scalar PDFs from experimental data based ... More

Information production in homogeneous isotropic turbulenceSep 08 2019We study the Reynolds number scaling of the Kolmogorov-Sinai entropy and attractor dimension for three dimensional homogeneous isotropic turbulence through the use of direct numerical simulation. To do so, we obtain Lyapunov spectra for a range of different ... More

Distributed flexibility in inertial swimmersSep 08 2019We study a linear inviscid model of a passively flexible swimmer with distributed flexibility, calculating its propulsive performance and optimal distributions of flexibility. The frequencies of actuation and mean stiffness ratios we consider span a large ... More

Soliton molecules and asymmetric solitons in fluid systems via velocity resonanceSep 08 2019Soliton molecules may be formed in some possible mechanisms in both theoretical and experimental aspects. In this letter, we introduce a new possible mechanism, the velocity resonant, to form soliton molecules. Under the resonant mechanism, two solitons ... More

Repetitive acoustic streaming patterns in sinusoidal shaped microchannelsSep 07 2019Geometry of the fluid container plays a key role in the shape of acoustic streaming patterns. Inadvertent vortices can be troublesome in some cases, but if treated properly, the problem turns into a very useful parameter in acoustic tweezing or micromixing ... More

Shape and size of large-scale vortices : a universal fluid pattern in geophysical fluid dynamicsSep 07 2019Planetary rotation organizes fluid motions into coherent, long-lived swirls, known as large scale vortices (LSVs). LSVs are ubiquitous in nature, and their shape and size are expected to control their effect on the dynamics and long-term evolution of ... More

Orientational instability and spontaneous rotation of active nematic dropletsSep 07 2019In experiments, an individual chemically active liquid crystal (LC) droplet submerged in the bulk of a surfactant solution may self-propel along a straight, helical, or random trajectory. In this paper, we develop a minimal model capturing all three types ... More

Transverse Force Induced by a Magnetized WakeSep 06 2019The force on a test charge moving through a strongly magnetized plasma is calculated using linear response theory. Strong magnetization is found to generate a component of the force perpendicular to the velocity of the particle in the plane formed by ... More

Analysis of the dissipative range of the energy spectrum in grid turbulence and in direct numerical simulationsSep 06 2019We present a statistical analysis of the behavior of the kinetic energy spectrum in the dissipative range of scales of fully developed three-dimensional turbulence. We analyze spectra recorded in experiments of grid turbulence generated in the Modane ... More

Macroscopic models for heterogeneous reactions in porous mediaSep 06 2019Sep 09 2019Derivation of coarse grained models for advection-diffusion processes in the presence of dominant surface reactions using homogenisation theory or volume averaging is often deemed unfeasible due to the strong coupling between scales that characterise ... More

Macroscopic models for heterogeneous reactions in porous mediaSep 06 2019The upscaling by homogenisation or volume averaging of advection-diffusion processes in the presence of dominant bulk or surface reactions is often deemed unfeasible [1, 2] due to the coupling between the scales that naturally appears. In this paper, ... More

First-principle hydrodynamics and kinetics for solvent-free coarse-grained membrane modelsSep 06 2019The great challenge with simulating bilayer membranes is the the wide range of scales involved, from nanometer/picosecond pertaining to individual lipids, to the micrometer/millisecond scale of biological membranes. While solvent-free coarse-grained membrane ... More

Notes on the two main routes of period doubling and 1/2 order subharmonic oscillations in a bubble oscillatorSep 06 2019Period doubling route to chaos is one of the well-known characteristics of nonlinear oscillators. A bubble is a highly nonlinear oscillator that exists in various phenomena and applications ranging from material science and underwater acoustics to medical ... More

Adaptive Third Order Adams-Bashforth Time Stepping Scheme for 2D Extended Boussinesq EquationsSep 05 2019We develop the third-order adaptive Adams-Bashforth time stepping scheme and the second-order finite difference discretization equation for variable time steps. We incorporate these schemes in the Celeris Advent software to discretize and solve the extended ... More

Reinterpreting Shock Wave Structure Predictions using the Navier-Stokes EquationsSep 05 2019Classical Navier-Stokes equations fail to predict shock wave profiles accurately. In this paper, the Navier-Stokes system is fully transformed using a velocity variable transformation. The transformed equations termed the re-casted Navier-Stokes equations ... More

Alignment of non-spherical active particles in chaotic flowsSep 05 2019We study the orientation statistics of spheroidal, axisymmetric microswimmers, with shapes ranging from disks to rods, swimming in chaotic, moderately turbulent flows. Numerical simulations show that rod-like active particles preferentially align with ... More

A well-balanced scheme for the simulation tool-kit A-MaZe: implementation, tests, and first applications to stellar structureSep 05 2019Characterizing stellar convection in multiple dimensions is a topic at the forefront of stellar astrophysics. Numerical simulations are an essential tool for this task. We present an extension of the existing numerical tool-kit A-MaZe that enables such ... More

Finding optimal hull shapes for fast vertical penetration into waterSep 05 2019A new approach for the supercavitating hull optimization was proposed, which combines the CFD simulation and analytical methods. The high-speed penetration into water at the velocity 1 km/s was considered with the fixed body mass and caliber. Six different ... More

Weak formulation and scaling properties of energy fluxes in 3D numerical turbulent Rayleigh-Bénard convectionSep 05 2019We apply the weak formalism on the Boussinesq equations, to characterize scaling properties of the mean and the standard deviation of the potential, kinetic and viscous energy flux in very high resolution numerical simulations. The local Bolgiano-Oboukhov ... More

Investigating viscous surface wave propagation modes and study of nonlinearities in a finite depth fluidSep 05 2019The object of this study is to investigate the effect of viscosity on propagation of free-surface waves in an incompressible viscous fluid layer of arbitrary depth. While we provide a more detailed study of properties of linear surface waves, the description ... More

Three-dimensional tracking of finite-size spheres in a turbulent boundary layerSep 04 2019The motion of individual magnetic wax spheres with specific gravities of 1.003, 1.050 and 1.150 was investigated in turbulent boundary layers with $Re_{{\tau}}=700$ and 1300 ($d^+ = 60$ and 120). The spheres were marked with dots all over the surface ... More

Dripping, jetting and tip streamingSep 04 2019Dripping, jetting and tip streaming have been studied up to a certain point separately by both fluid mechanics and microfluidics communities, the former focusing on fundamental aspects while the latter on applications. Here, we intend to review this field ... More

Benchmarking of a preliminary MFiX-Exa codeSep 04 2019MFiX-Exa is a new code being actively developed at Lawrence Berkeley National Laboratory and the National Energy Technology Laboratory as part of the U.S. Department of Energy's Exascale Computing Project. The starting point for the MFiX-Exa code development ... More

Rayleigh-Taylor unstable flames at higher Reynolds numberSep 04 2019Rayleigh-Taylor (RT) unstable flames are a key component of Type Ia and Iax supernovae explosions, but their complex hydrodynamics is still not well understood. These flames are affected not only by the RT instability, but also by the turbulence it generates. ... More

Leray turbulence: what can we learn from acceleration compared to velocitySep 04 2019In a recent paper we presented evidence for the occurence of Leray-like singularities with positive Sedov-Taylor exponent $\alpha$ in turbulent flows recorded in Modane's wind tunnel, by looking at simultaneous acceleration and velocity records. Here ... More

Thermal transients in a U-BendSep 04 2019We study numerically the propagation of a hot thermal transient through a U-bend via an ensemble of wall-resolved large eddy simulations. Conjugate heat transfer between fluid and solid domains is accounted for. The flow is in a fully turbulent mixed ... More

Shadowing the rotating annulus. Part I: Measuring candidate trajectory shadowing timesSep 04 2019An intuitively necessary requirement of models used to provide forecasts of a system's future is the existence of shadowing trajectories that are consistent with past observations of the system: given a system-model pair, do model trajectories exist that ... More

A novel subcritical transition to turbulence in Taylor-Couette flow with counter-rotating cylindersSep 03 2019The transition to turbulence in Taylor-Couette flow often occurs via a sequence of supercritical bifurcations to progressively more complex, yet stable, flows. We describe a subcritical laminar-turbulent transition in the counter-rotating regime mediated ... More

Streaming controlled by meniscus shapeSep 03 2019Surface waves called meniscus waves often appear in the systems that are close to the capillary length scale. Since the meniscus shape determines the form of the meniscus waves, the resulting streaming circulation has a structure distinct from that caused ... More

Stable mixing estimates in the infinite Péclet number limitSep 03 2019We consider a passive scalar $f$ advected by a strictly monotone shear flow and with a diffusivity parameter $\nu\ll 1$. We prove an estimate on the homogeneous $\dot{H}^{-1}$ norm of $f$ that combines both the $L^2$ enhanced diffusion effect at a sharp ... More