Latest in physics.flu-dyn

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Bees with attitude: the effect of gusts on flight dynamicsFeb 10 2018Flight is a complicated task at small scales in part due to the ubiquitous unsteady air which contains it. Flying organisms deal with these difficulties using active and passive control mechanisms to steer their body motion. Body attitudes of flapping ... More
Capillary-driven binding of thin triangular prisms at fluid interfacesFeb 08 2018We observe capillary-driven binding between thin, equilateral triangular prisms at a flat air-water interface. The edge length of the equilateral triangle face is 120 $\mu m$, and the thickness of the prism is varied between 2 and 20 $\mu m$. For thickness ... More
A discrete unified gas-kinetic scheme for immiscible two-phase flowsFeb 08 2018In this work, we extend the discrete unified gas-kinetic scheme (DUGKS) [Guo et al., Phys. Rev. E 88, 033305 (2013)] to continue two-phase flows. In the framework of DUGKS, two kinetic model equations are used to solve the quasi-incompressible phase-field ... More
Numerical simulation of electrically-driven flows using $\text{OpenFOAM}^\circledR$Feb 08 2018In this work, we study the implementation of electrically-driven flow (EDF) models in the finite-volume framework of $\text{OpenFOAM}^\circledR$. The Poisson-Nernst-Planck model is used for the transport of charged species and it is coupled to the Navier-Stokes ... More
Implementation of a geometrically and energetically constrained mesoscale eddy parameterization in an ocean circulation modelFeb 08 2018The global stratification and circulation of the ocean and their sensitivities to changes in forcing depend crucially on the representation of the mesoscale eddy field. Here, a geometrically informed and energetically constrained parameterization framework ... More
Crossroads of the mesoscale circulationFeb 08 2018Quantifying the mechanisms of tracer dispersion in the ocean remains a central question in oceanography, for problems ranging from nutrient delivery to phytoplankton, to the early detection of contaminants. Until now, most of the analysis has been based ... More
Fourier Analysis and Evaluation of DG, FD and Compact Difference Methods for Conservation LawsFeb 08 2018Large eddy simulation (LES) has been increasingly used to tackle vortex-dominated turbulent flows. In LES, the quality of the simulation results hinges upon the quality of the numerical discretizations in both space and time. It is in this context we ... More
Efficient collective swimming by harnessing vortices through deep reinforcement learningFeb 07 2018Fish in schooling formations navigate complex flow-fields replete with mechanical energy in the vortex wakes of their companions. Their schooling behaviour has been associated with evolutionary advantages including collective energy savings. How fish ... More
A Morphing Continuum Analysis of Energy Transfer in Compressible TurbulenceFeb 07 2018A shock-preserving finite volume solver with the generalized Lax-Friedrichs splitting flux for Morphing Continuum Theory (MCT) is presented and verified. The numerical MCT solver is showcased in a supersonic turbulent flow with Mach 2.93 over an $8^{\circ}$ ... More
A general tool for LTE thermochemistry for adiabatic nondiffusive fluid dynamics: applications to 2D planar discontinuity flows in SPHFeb 07 2018Chemical reactions in fluid dynamics deeply modify the flow physical conditions through both the contribution of the energy of reactions and the variation of the mean molecular weight and of the ratio of specific heats. This occurs typically on time scales ... More
Entrainment and mixing in gravity currents using simultaneous velocity-density measurementsFeb 07 2018Gravity currents modify their flow characteristics by entraining ambient fluid, which depends on a variety of governing parameters such as the initial density, $\Delta \rho$, the total initial height of the fluid, $H$, and the slope of the terrain, $\alpha$, ... More
Turbulent Cascade Direction and Lagrangian Time-AsymmetryFeb 07 2018We establish Lagrangian formulae for energy conservation anomalies involving the discrepancy between short-time two-particle dispersion forward and backward in time. These results are facilitated by a rigorous version of the Ott-Mann-Gaw\c{e}dzki relation, ... More
Conformal invariance and the Lundgren-Monin-Novikov equations for vorticity fields in 2D turbulence: Refuting a recent claimFeb 06 2018The recent claim by Grebenev et al. [J. Phys. A: Math. Theor. 50, 435502 (2017)] that the inviscid 2D Lundgren-Monin-Novikov (LMN) equations on a zero vorticity characteristic naturally would reveal local conformal invariance when only analyzing these ... More
Kinematics of a Fluid Ellipse in a Linear FlowFeb 06 2018A four-parameter kinematic model for the position of a fluid parcel in a time-varying ellipse is introduced. For any ellipse advected by an arbitrary linear two-dimensional flow, the rates of change of the ellipse parameters are uniquely determined by ... More
Elastoviscoplastic flow in porous mediaFeb 06 2018We investigate the elastoviscoplastic flow through porous media by numerical simulations. We solve the Navier-Stokes equations combined with the elastoviscoplastic model proposed by Saramito for the stress tensor evolution. In this model, the material ... More
Complexity of the laminar-turbulent boundary in pipe flowFeb 06 2018Over the past decade, the edge of chaos has proven to be a fruitful starting point for investigations of shear flows when the laminar base flow is linearly stable. Numerous computational studies of shear flows demonstrated the existence of states that ... More
Motility induces a double positive effect of E. coli dispersion in porous mediaFeb 06 2018The role of motility on the hydrodynamic dispersion of bacteria in a porous media is here studied by tracking thousands of bacteria in a microfluidic chip containing randomly placed obstacles. We first evaluate the dynamics of the spreading of two populations ... More
Pressure-driven dynamics of liquid plugs in rectangular microchannels: influence of the transition between static and dynamic film deposition regimesFeb 06 2018In this paper, we study experimentally and theoretically the dynamics of liquid plugs in rectangular microchannels for both unidirectional and cyclic pressure forcing. In both cases, it is shown that the transition between static and dynamic film deposition ... More
Ion Transport and Precipitation Kinetics as Key Aspects of Stress Generation on Pore Walls Induced by Salt CrystallizationFeb 06 2018The stress generation on pore walls due to the growth of a sodium chloride crystal in a confined aqueous solution is studied from evaporation experiments in microfluidic channels in conjunction with numerical computations of crystal growth. The study ... More
Efficiency of high-performance discontinuous Galerkin spectral element methods for under-resolved turbulent incompressible flowsFeb 05 2018The present paper addresses the numerical solution of turbulent flows with high-order discontinuous Galerkin methods for discretizing the incompressible Navier-Stokes equations. The efficiency of high-order methods when applied to under-resolved problems ... More
Relaminarization by steady modification of the streamwise velocity profile in a pipeFeb 05 2018We show that a rather simple, steady modification of the streamwise velocity profile in a pipe can lead to a complete collapse of turbulence and the flow fully relaminarizes. Two different devices, a stationary obstacle (inset) and a device to inject ... More
Jet mixing optimization using machine learning controlFeb 05 2018We experimentally optimize mixing of a turbulent round jet using machine learning control (MLC) following Li et al (2017). The jet is manipulated with one unsteady minijet blowing in wall-normal direction close to the nozzle exit. The flow is monitored ... More
Formation of eyes in large-scale cyclonic vorticesFeb 04 2018We present numerical simulations of steady, laminar, axisymmetric convection of a Boussinesq fluid in a shallow, rotating, cylindrical domain. The flow is driven by an imposed vertical heat flux and shaped by the background rotation of the domain. The ... More
Model and Solution of Darcy's Law: Homogeneous and Inhomogeneous MediaFeb 03 2018Using a mathematical analytic scheme we present a model of groundwater dynamics, given as usual in terms of partial differential equations whose solution requires the implementation of boundary conditions under physical basis. The final aim is to model ... More
Nonlinear resonances in the $ABC$-flowFeb 02 2018In this paper we study resonances of the $ABC$-flow in the near integrable case ($C\ll 1$). This is an interesting example of a Hamiltonian system with 3/2 degrees of freedom in which simultaneous existence of two resonances of the same order is possible. ... More
Analysis of stationary points and their bifurcations in the ABC flowFeb 02 2018Analytical expressions for coordinates of stationary points and conditions for their existence in the ABC flow are received. The type of the stationary points is shown analytically to be saddle-node. Exact expressions for eigenvalues and eigenvectors ... More
Propelled micro-probes in turbulenceFeb 01 2018Feb 06 2018The temporal statistics of incompressible fluid velocity and passive scalar fields in developed turbulent conditions is investigated by means of direct numerical simulations along the trajectories of self-propelled point-like probes drifting in a flow. ... More
Optimized cell geometry for buffer-gas-cooled molecular-beam sourcesJan 31 2018We have designed, constructed, and commissioned a cryogenic helium buffer-gas source for producing a cryogenially-cooled molecular beam and evaluated the effect of different cell geometries on the intensity of the produced molecular beam, using ammonia ... More
Two-dimensional vortex quantum dropletsJan 31 2018It was recently found that the Lee-Huang-Yang (LHY) correction to the mean-field Hamiltonian suppresses the collapse and creates stable localized modes (two-component "quantum droplets", QDs) in two and three dimensions. We construct two-dimensional\ ... More
An Analysis of the Convergence of Stochastic Lagrangian/Eulerian Spray SimulationsJan 30 2018This work derives how the convergence of stochastic Lagrangian/Eulerian simulations depends on the number of computational parcels, particularly for the case of spray modeling. A new, simple, formula is derived that can be used for managing the numerical ... More
Hill's Spherical Vortex in a Rotating FluidJan 30 2018A popular model for a generic fat-cored vortex ring or eddy is Hill's spherical vortex (Phil. Trans. Roy. Soc. A vol. 185, 1894, p. 213). Here we find an exact solution for such a spherical vortex steadily propagating along the axis of a rotating ideal ... More
Microtransformers: controlled microscale navigation with flexible robotsJan 29 2018Artificial microswimmers are a new technology with promising microfluidics and biomedical applications, such as directed cargo transport, microscale assembly, and targeted drug delivery. A fundamental barrier to realising this potential is the ability ... More
Numerically Modelling Stochastic Lie Transport in Fluid DynamicsJan 29 2018We present a numerical investigation of stochastic transport in ideal fluids. According to Holm (Proc Roy Soc, 2015) and Cotter et al. (2017), the principles of transformation theory and multi-time homogenisation, respectively, imply a physically meaningful, ... More
A multi-scale limit of a randomly forced rotating $3$-D compressible fluidJan 29 2018We study a singular limit of a scaled compressible Navier--Stokes--Coriolis system driven by both a deterministic and stochastic forcing terms in three dimensions. If the Mach number is comparable to the Froude number with both proportional to say $\varepsilon\ll ... More
Impact of roughness on the instability of a free-cooling granular gasJan 29 2018A linear stability analysis of the hydrodynamic equations with respect to the homogeneous cooling state is carried out to identify the conditions for stability of a granular gas of rough hard spheres. The description is based on the results for the transport ... More
Origins of liquid-repellency on structured, flat, and lubricated surfacesJan 29 2018There are currently three main classes of high-performance liquid-repellent surfaces: micro-/nano-structured lotus-effect superhydrophobic surfaces, flat surfaces grafted with 'liquid-like' polymer brushes, and various lubricated surfaces. Despite recent ... More
Theoretical bounds for the exponent in the empirical power-law advance-time curve for surface flowJan 28 2018A fundamental and widely applied concept used to study surface flow processes is the advance-time curve characterized by an empirical power law with an exponent r and a numerical prefactor p (i.e., x = p*t^r). In the literature, different values of r ... More
Decay of Kadomtsev - Petviashvili lumps in dissipative mediaJan 28 2018The decay of Kadomtsev - Petviashvili lumps is considered for a few typical dissipations - Rayleigh dissipation, Reynolds dissipation, Landau damping, Chezy bottom friction, viscous dissipation in the laminar boundary layer, and radiative losses caused ... More
Decay of Benjamin - Ono solitons under the influence of dissipationJan 27 2018The adiabatic decay of Benjamin - Ono algebraic solitons is studied when the influence of various types of small dissipation and radiative losses due to large scale Coriolis dispersion are taken into consideration. The physically most important dissipations ... More
Soliton spectra of random water waves in shallow basinsJan 27 2018Interpretation of random wave field on a shallow water in terms of Fourier spectra is not adequate, when wave amplitudes are not infinitesimally small. A nonlinearity of wave fields leads to the harmonic interactions and random variation of Fourier spectra. ... More
Soliton solutions to the fifth-order Korteweg - de Vries equation and their applications to surface and internal water wavesJan 27 2018Jan 31 2018We study solitary wave solutions of the fifth-order Korteweg - de Vries equation which contains, besides the traditional quadratic nonlinearity and third-order dispersion, additional terms including cubic nonlinearity and fifth order linear dispersion, ... More
Mean-field theory of differential rotation in density stratified turbulent convectionJan 26 2018A mean-field theory of differential rotation in a density stratified turbulent convection has been developed. This theory is based on a combined effect of the turbulent heat flux and anisotropy of turbulent convection increasing with the rate of rotation ... More
Edge-induced shear banding in entangled polymeric fluidsJan 26 2018Despite decades of research, the question of whether solutions and melts of highly entangled polymers exhibit shear banding as their steady state response to a steadily imposed shear flow remains controversial. From a theoretical viewpoint, an important ... More
Time-delayed feedback control of shear-driven micellar systemsJan 26 2018Feb 05 2018Suspensions of elongated micelles under shear display complex non-linear behaviour including shear banding, spatio-temporal oscillatory patterns and chaotic response. Based on a suitable rheological model [S. M. Fielding and P. D. Olmsted, Phys. Rev. ... More
Self-bound droplets of light with orbital angular momentumJan 25 2018Systems with competing attractive and repulsive interactions have a tendency to condense into droplets. This is the case for water in a sink, liquid helium and dipolar atomic gases. Here, we consider a photon fluid which is formed in the transverse plane ... More
Algebraic multigrid preconditioners for two-phase flow in porous media with phase transitionsJan 25 2018Multiphase flow is a critical process in a wide range of applications, including oil and gas recovery, carbon sequestration, and contaminant remediation. Numerical simulation of multiphase flow requires solving of a large, sparse linear system resulting ... More
Dynamic Control of Particle Deposition in Evaporating Droplets by an External Point Source of VaporJan 24 2018The deposition of particles on a surface by an evaporating sessile droplet is important for phenomena as diverse as printing, thin-film deposition and self-assembly. The shape of the final deposit depends on the flows within the droplet during evaporation. ... More
Robust and efficient discontinuous Galerkin methods for under-resolved turbulent incompressible flowsJan 24 2018We present a robust and accurate discretization approach for incompressible turbulent flows based on high-order discontinuous Galerkin methods. The DG discretization of the incompressible Navier-Stokes equations uses the local Lax-Friedrichs flux for ... More
Hamiltonian fluid dynamics and distributed chaosJan 23 2018It is shown that distributed chaos with spontaneously broken time translational symmetry (homogeneity) has a stretched exponential frequency spectrum $E(f) \propto \exp-(f/f_0)^{1/2}$. Good agreement has been established with a laboratory experimental ... More
The vortex doublet as a generating mechanism of inviscid vortex sheets. Part I: separation at a sharp edgeJan 22 2018In two-dimensional flow, the vortex sheet corresponding to inviscid flow separation at a sharp edge is generated by a vortex doublet, which arises as a result of representing the solid surfaces as vortex doublet sheets. Namely, the inviscid limit of the ... More
Negative absolute temperatures of vortices in a two-dimensional superfluidJan 22 2018We have observed negative absolute temperature configuration of vortices in a 2D superfluid atomic gas of Rb atoms confined in a circular-shaped, flat-bottom potential. We create the vortex configurations by sweeping a linear array of optical barriers ... More
Negative-Temperature Onsager Vortex Clusters in a Quantum FluidJan 22 2018Turbulence in classical fluids is a ubiquitous non-equilibrium phenomenon, yet a complete theoretical description for turbulent flow remains a challenging problem. A useful simplification for ideal two-dimensional (2D) fluids is to describe the turbulent ... More
Hurricane's Maximum Potential Intensity and the Gravitational Power of PrecipitationJan 21 2018The concept of Maximum Potential Intensity (MPI) is widely used in tropical cyclone research to estimate the minimum central pressure and the maximum velocity of tropical storms from environmental parameters. The MPI pressure derives from consideration ... More
Classification of Machine Learning Frameworks for Data-Driven Thermal Fluid ModelsJan 20 2018Thermal fluid processes are inherently multi-physics and multi-scale, involving mass-momentum-energy transport phenomena. Thermal fluid simulation (TFS) is based on solving conservative equations, for which - except for "first-principle" direct numerical ... More
Competitive dynamics of two erosion patterns around a cylinderJan 17 2018Jan 26 2018We investigate experimentally the local erosion of a granular bed near a fixed vertical cylinder that emerges from the bed. The onset of erosion arising at the base of the cylinder and usually ascribed to the wrapping horseshoe vortex is determined and ... More
Anomalous Exponents in Strong Turbulence in an Infinite Fluid Driven by a Gaussian Random ForceJan 17 2018To characterize fluctuations in a turbulent flow, one usually studies different moments of velocity increments and/or dissipation rate, $\overline{(v(x+r)-v(x))^{n}}\propto r^{\zeta_{n}}$ and $\overline{{\cal E}^{n}}\propto Re^{d_{n}}$, respectively. ... More
The simultaneous discharge of liquid and grains from a siloJan 17 2018The flow rate of water through an orifice at the bottom of a container depends on the hydrostatic pressure whereas for a dry granular material is nearly constant. But what happens during the simultaneous discharge of grains and liquid from a silo? By ... More
Self-Consistent Description of Local Density Dynamics in Simple Liquids. The Case of Molten LithiumJan 15 2018The dynamic structure factor is the quantity, which can be measured by means of Brillouin light-scattering as well as by means of inelastic scattering of neutrons and X-rays. The spectral (or frequency) moments of the dynamic structure factor define directly ... More
Long-lived quantum vortex knotsJan 15 2018Dynamics of simplest quantum vortex knots of torus type in a superfluid at zero temperature has been simulated within a regularized Biot-Savart law (the torus radii $R_0$ and $r_0$ for initial vortex configuration were large in comparison with a vortex ... More
Negative-mass effects in spin-orbit coupled Bose-Einstein condensatesJan 15 2018Negative effective masses can be realised by engineering the dispersion relation in a variety of quantum systems. A recent experiment with spin-orbit coupled Bose-Einstein condensates has shown that a negative effective mass can halt the free expansion ... More
The ultimate state for heat transfer between two parallel platesJan 14 2018The incompressible time-independent velocity field has been determined so as to maximize heat transfer between two parallel plates of a constant temperature difference under the constraint of fixed total enstrophy. The present variational problem is the ... More
Turbulent superstructures in Rayleigh-Bénard convectionJan 13 2018Turbulent Rayleigh-B\'enard convection displays a large-scale order in the form of rolls and cells on lengths larger than the layer height once the fluctuations of temperature and velocity are removed. These turbulent superstructures are reminiscent of ... More
Experimental Confirmation of the Magnetorotational Instability MechanismJan 10 2018The Magnetorotational Instability (MRI) has long been considered a plausibly ubiquitous mechanism to destabilize Keplerian flows, transport angular momentum, and facilitate fast accretion in astrophysical objects. But heretofore, experimental validation ... More
Deformation of a biconcave-discoid capsule in extensional flow and electric fieldJan 06 2018Biconcave-discoid (empirical shape of a red blood cell) capsule finds numerous applications in the field of bio-fluid dynamics and rheology, apart from understanding the behavior of red blood cells (RBC) in blood flow. A detailed analysis is, therefore, ... More
Generation of large-scale vorticity in rotating stratified turbulence with inhomogeneous helicity: mean-field theoryJan 01 2018We discuss a mean-field theory of generation of large-scale vorticity in a rotating density stratified developed turbulence with inhomogeneous kinetic helicity. We show that the large-scale nonuniform flow is produced due to ether a combined action of ... More
Electrochemical membrane microactuator with a millisecond response timeJan 01 2018Lack of fast and strong actuators to drive microsystems is well recognized. Electrochemical actuators are considered attractive for many applications but they have long response time (minutes) due to slow gas termination. Here an electrochemical actuator ... More
Compressibility effects in turbulent MHD and passive scalar transport: mean-field theoryDec 30 2017We develop a mean-field theory of compressibility effects in turbulent magnetohydrodynamics and passive scalar transport using the quasi-linear approximation and the spectral $\tau$-approach. We find that compressibility decreases the $\alpha$ effect ... More
Moment Approximations and Model Cascades for Shallow FlowDec 29 2017Shallow flow models are used for a large number of applications including weather forecasting, open channel hydraulics and simulation-based natural hazard assessment. In these applications the shallowness of the process motivates depth-averaging. While ... More
Particle Ice Front Interaction - The Brownian Ratchet ModelDec 29 2017We treat the problem of particle pushing by growing ice as a free diffusion near a wall that moves with discrete steps. When the particle diffuse away from the surface the surface can grow, blocking the particle from going back. Elementary calculations ... More
Universal scaling of extreme vorticity regions and the structure of the vortex lines representationDec 28 2017The incompressible three-dimensional ideal flows develop very thin pancake-like regions of increasing vorticity, which evolve with the scaling \omega_{\max}\propto\ell^{-2/3} between the vorticity maximum and the pancake thickness. We study this process ... More
Spinning and tumbling of micron-sized triangles in a micro-channel shear flowDec 22 2017We report on measurements of the angular dynamics of micron-sized equilaterally triangular platelets suspended in a micro-channel shear flow. Our measurements confirm that such particles spin and tumble like a spheroid in a simple shear. Since the triangle ... More
A nested polyhedra model of isotropic MHD turbulenceDec 22 2017A nested polyhedra model has been developed for magnetohydrodynamic (MHD) turbulence. Driving only the velocity field at large scales with random, divergence free forcing results in a clear, stationary $k^{-5/3}$ spectrum for both kinetic and magnetic ... More
Simulation and stability analysis of oblique shock wave/boundary layer interactions at Mach 5.92Dec 21 2017We investigate flow instability created by an oblique shock wave impinging on a Mach 5.92 laminar boundary layer at a transitional Reynolds number. The adverse pressure gradient of the oblique shock causes the boundary layer to separate from the wall, ... More
Converging Shock Flows for a Mie-Grüneisen Equation of StateDec 21 2017Previous work has shown that the one-dimensional (1D) inviscid compressible flow (Euler) equations admit a wide variety of scale-invariant solutions (including the famous Noh, Sedov, and Guderley shock solutions) when the included equation of state (EOS) ... More
Atmospheric Circulations of Hot Jupiters as Planetary Heat EnginesDec 20 2017Because of their intense incident stellar irradiation and likely tidally locked spin states, hot Jupiters are expected to have wind speeds that approach or exceed the speed of sound. In this work we develop a theory to explain the magnitude of these winds. ... More
Collapsing cavities and converging shocks in non-ideal materialsDec 20 2017As modern hydrodynamic codes increase in sophistication, the availability of realistic test problems becomes increasingly important, but their very nature is usually unrealistic because they must be simple enough to be understood without computer aid. ... More
Particle-Pair Relative Velocity Measurement in High-Reynolds-Number Homogeneous and Isotropic Turbulence Using 4-Frame Particle Tracking VelocimetryDec 20 2017The radial relative velocity between particles suspended in turbulent flow plays a critical role in droplet collision and growth. We present a simple and accurate approach to RV measurement in isotropic turbulence - planar 4-frame particle tracking velocimetry ... More
Direct simulation of liquid-gas-solid flow with a free surface lattice Boltzmann methodDec 19 2017Direct numerical simulation of liquid-gas-solid flows is uncommon due to the considerable computational cost. As the grid spacing is determined by the smallest involved length scale, large grid sizes become necessary -- in particular if the bubble-particle ... More
Metric for attractor overlapDec 03 2017We present the first general metric for attractor overlap (MAO) facilitating an unsupervised data comparison. The starting point is two or more attractors, i.e. ensembles of states representing different operating conditions. The proposed metric quantifies ... More
An energy-based equilibrium contact angle boundary condition on jagged surfaces for phase-field methodsNov 15 2017We consider an energy-based boundary condition to impose an equilibrium wetting angle for the Cahn-Hilliard-Navier-Stokes phase-field model on voxel-set-type computational domains. These domains typically stem from the micro-CT imaging of porous rock ... More
Turbulence statistics in a 2D vortex condensateNov 15 2017Disentangling the evolution of a coherent mean-flow and turbulent fluctuations, interacting through the non-linearity of the Navier-Stokes equations, is a central issue in fluid mechanics. It affects a wide range of flows, such as planetary atmospheres, ... More
Multi-component lattice Boltzmann models for accurate simulation of flows with wide viscosity variationNov 09 2017Multi-component lattice Boltzmann models operating in a wide range of fluid viscosity values are developed and examined. The algorithm is constructed with the goal to enable engineering applications without sacrificing simplicity and computational efficiency ... More
The culmination of an inverse cascade: mean flow and fluctuationsOct 25 2017Feb 01 2018Two dimensional turbulence has a remarkable tendency to self-organize into large, coherent structures, forming a mean flow. The purpose of this paper is to elucidate how these structures are sustained, and what determines them and the fluctuations around ... More
Calculations for the Practical Applications of Quadratic Helicity in MHDOct 24 2017For the quadratic helicity $\chi^{(2)}$ we present a generalization of the Arnol'd inequality which relates the magnetic energy to the quadratic helicity, which poses a lower bound. We then introduce the quadratic helicity density using the classical ... More
A complete equation of state for non-ideal condensed phase explosivesOct 10 2017Dec 15 2017The objective of this work is to improve the robustness and accuracy of numerical simulations of both ideal and non-ideal explosives by introducing temperature dependence in mechanical equations of state for reactants and products. To this end, we modify ... More
Dynamo Action in a Quasi-Keplerian Taylor-Couette FlowAug 25 2017Oct 06 2017We numerically compute the flow of an electrically conducting fluid in a Taylor-Couette geometry where the rotation rates of the inner and outer cylinders satisfy $\Omega_o/\Omega_i=(r_o/r_i)^{-3/2}$. In this quasi-Keplerian regime a non-magnetic system ... More
Influence of the approach boundary layer on the flow over an axisymmetric hill at a moderate Reynolds numberAug 23 2017Large Eddy Simulations of a flow at a moderate Reynolds number over and around a three-dimensional hill have been performed. The main aim of the simulations was to study the effects of various inflow conditions (boundary layer thickness and laminar versus ... More
Superposition solutions to the extended KdV equation for water surface wavesAug 20 2017The KdV equation can be derived in the shallow water limit of the Euler equations. Over the last few decades, this equation has been extended to include higher order effects. Although this equation has only one conservation law, exact periodic and solitonic ... More
A numerical study of a variable-density low-speed turbulent mixing layerAug 15 2017Direct numerical simulations of a temporally-developing, low-speed, variable-density, turbulent, plane mixing layer are performed. The Navier-Stokes equations in the low-Mach number approximation are solved using a novel algorithm based on an extended ... More
Boundary-Conforming Free-Surface Flow Computations: Interface Tracking for Linear, Higher-Order and Isogeometric Finite ElementsAug 14 2017The simulation of certain flow problems requires a means for modeling a free fluid surface; examples being viscoelastic die swell or fluid sloshing in tanks. In a finite-element context, this type of problem can, among many other options, be dealt with ... More
Bounding Surface Integral Of Functions Dragged By Velocity FieldsJul 28 2017Aug 31 2017To find bounded magnitudes is essential in dynamical systems when they evolve over time. Particularly, the problem of bounded kinetic energy for velocity fields has received increasing attention on this type of systems. Here it is reasoned how to tie ... More
On the aerodynamic forces on heaving and pitching airfoils at low Reynolds numberJul 24 2017The influence that the kinematics of pitching and heaving 2D airfoils have on the aerodynamic forces is investigated using Direct Numerical Simulations and a force decomposition algorithm. Large amplitude motions are considered (of the order of one chord), ... More
Turbulent Mass Inhomogeneities induced by a point-sourceJul 20 2017Dec 01 2017We describe how turbulence distributes tracers away from a localized source of injection, and analyse how the spatial inhomogeneities of the concentration field depend on the amount of randomness in the injection mechanism. For that purpose, we contrast ... More
Bulk viscosity model for near-equilibrium acoustic wave attenuationJul 18 2017Acoustic wave attenuation due to vibrational and rotational molecular relaxation, under simplifying assumptions of near-thermodynamic equilibrium and absence of molecular dissociations, can be accounted for by specifying a bulk viscosity coefficient $\mu_B$. ... More
Lagrangian Transport Through Surfaces in Compressible FlowsJul 03 2017Sep 28 2017A material-based, i.e., Lagrangian, methodology for exact integration of flux by volume-preserving flows through a surface has been developed recently in [Karrasch, SIAM J. Appl. Math., 76 (2016), pp. 1178-1190]. In the present paper, we first generalize ... More
Sparse reduced-order modeling : Sensor-based dynamics to full-state estimationJun 12 2017We propose a general dynamic reduced-order modeling framework for typical experimental data: time-resolved sensor data and optional non-time-resolved PIV snapshots. This framework contains four steps. First, the sensor signals are lifted to a dynamic ... More
A wall-function approach for direct precipitation/crystallization fouling in cfd modellingJun 09 2017The main objective of this paper is to present a generic modelling framework, for the diffusive mass transport through the turbulent, reactive boundary layer of multi-component fluid mixtures that precipitate on the wall. The modelling is based on Maxwell-Stefan ... More
Impact of cyclostationarity on fan broadband noise predictionJun 01 2017One of the dominant noise sources of modern Ultra High Bypass Ratio (UHBR) engines is the interaction of the rotor wakes with the leading edges of the stator vanes in the fan stage. While the tonal components of this noise generation mechanism are fairly ... More
Transport properties of the Azimuthal Magnetorotational InstabilityMay 10 2017Oct 05 2017The magnetorotational instability (MRI) is thought to be a powerful source of turbulence in Keplerian accretion disks. Motivated by recent laboratory experiments, we study the MRI driven by an azimuthal magnetic field in an electrically conducting fluid ... More
Linear genetic programming control for strongly nonlinear dynamics with frequency crosstalkApr 30 2017We advance Machine Learning Control (MLC), a recently proposed model-free control framework which explores and exploits strongly nonlinear dynamics in an unsupervised manner. The assumed plant has multiple actuators and sensors and its performance is ... More