Vortical dynamics of spinning quantum plasmas: helicity conservation

It is shown that a vorticity, constructed from the spin field of a quantum spinning plasma, combines with the classical generalized vorticity (representing the magnetic and the velocity fields) to yield a new grand generalized vorticity that obeys the standard vortex dynamics. Expressions for the quantum or spin vorticity and for the resulting generalized helicity invariant are derived. Reduction of the rather complex spinning quantum system to a well known and highly investigated classical form opens familiar channels for the delineation of physics peculiar to dense plasmas spanning solid state to astrophysical objects. A simple example is worked out to show that the magnetics of a spinning plasma can be much richer than that of the corresponding classical system.     

Vortex dynamics in the wake of a magnetic obstacle

We present an experimental study about the vortex dynamics in liquid metal flow under the influence of confined non-homogeneous magnetic field, so-called magnetic obstacle. A permanent magnet installed on a moving rail beneath a cell, filled with eutectic alloy GaInSn, moves with constant velocities with the corresponding Reynolds number from \(Re = \text{125 to 2000}\) . The liquid metal flow patterns are recorded using a camera moving with the magnet. Small bubbles, which are a product of hydrochloric acid and GaInSn oxide reaction, illuminate the streamlines which are to be presented here. As the velocity and hence Reynolds number and interaction parameter change, complicated phenomena are visible inside the channel including formation of vortices or their suppression, symmetry breakdown, vortex duplication and vortex shedding. The vast number of instability-related phenomena present in the flow past a magnetic obstacle make it worth investigating. This leads to a better understanding of magnetic obstacle or even turbulence. Since it is impossible to present all the observed phenomena in detail in one paper, here we present only a few illustrative examples to provide an overall view of the phenomena occurring. We conclude with a discussion of the flow instabilities and comparison between the results of our experiments and the theoretical predictions of the reference literature.     

Vortical gust boundary condition for realistic rotor wake/stator interaction noise prediction using computational aeroacoustics

In this work, the NASA Glenn Research Center Broadband Aeroacoustic Stator Simulation (BASS) code is extended for use in the prediction of noise produced by realistic three-dimensional rotor wakes impinging on a downstream stator row. In order to accurately simulate such a flow using a nonlinear time-accurate solver, the inflow and outflow boundary conditions must simultaneously maintain the desired mean flow, allow outgoing vortical, entropic, and acoustic waves to cleanly exit the domain, and accurately impose the desired incoming flow disturbances. This work validates a new method for the acoustics-free imposition of three-dimensional vortical disturbances using benchmark test cases.     

Plasma ions dynamics in the wake of a short laser pulse

A new physical effect of a plasma channel formation by the ponderomotive force of a wakefield generated by a laser pulse with a length of the order of the electron plasma wavelength is discussed. For a narrow pulse, wherein the width is less than c/omega(pe) ( omega(pe) and c are the plasma frequency and light velocity, respectively), the channel has an annular form with on-axis density maximum. The depth of the channel increases with the distance from the pulse until the phase mixing arises and the wake starts to break. The linear fluid theory is used to obtain the scaling for wave-breaking conditions. The results of numerical simulations for high intensity laser pulses are in good agreement with theoretical predictions.     

Numerical simulation of momentumless turbulent wake dynamics in linearly stratified medium

This paper presents comparison of two numerical models of the momentumless turbulent wake dynamics behind a body of revolution in a linearly stratified medium, namely, the model based on direct (DNS) numerical integration of Navier–Stokes equations in the Oberbeck–Boussinesq approximation and the mathematical model with application of a semi-empirical turbulence model of the third order. The results of calculations by these two models agree with the known experimental data.     

Structure and dynamics of edge flames in the near wake of unequal merging shear flows

We examine in this study the structure and dynamic properties of an edge flame formed in the near-wake of two initially separated shear flows, one containing fuel and the other oxidiser. A comprehensive study is carried out within the diffusive-thermal framework where the flow field, computed a-priori, is used for the determination of the combustion field. Our focus is on the effects of three controlling parameters: the Damköhler number controlling the overall flow rate, the oxidiser-to-fuel strain rate ratio of the supply streams that determines the extent of oxidiser entrainment towards the mixing zone, and the Lewis number, assumed equal for the fuel and oxidiser, that depends on the mixture composition. Response curves, representing the edge flame standoff distance as a function of Damköhler number, exhibit two distinct shapes: C-shaped and U-shaped curves characterising the response of low and high Lewis number flames, respectively. Stability considerations show that the upper solution branch of the C-shaped response curve is unstable and hence corresponds to physically unrealistic states, but due to heat conduction toward the cold plate the lower solution branch is always stable. The states forming this solution branch correspond to flame attachment, where the edge flame remains practically attached to the tip of the plate until it is blown off by the flow when the velocity exceeds a critical value. The U-shaped response, on the other hand, consists of equilibrium states that are globally stable. Thus, high Lewis number flames can be always stabilised near the splitter plate, with the edge held stationary or undergoing a back and forth motion, or lifted and stabilised downstream by the flow. Insight into the distinct stabilisation characteristics, exhibited by the different Lewis number cases, is given by examining the relationship between the local flow velocity and the edge propagation speed.     

On the variable order dynamics of the nonlinear wake caused by a sedimenting particle

In this work we develop a variable order (VO) differential equation of motion for a spherical particle sedimenting in a quiescent viscous liquid. In particular, we examine the various force terms in the equation of motion and propose a new form for the history drag acting on the particle. We show that the variable order formulation allows for an effective way to express the dynamic transition of the dominant forces over the entire time of the motion of the particle from rest to terminal velocity. The use of VO operators also allows us to examine the evolving dynamics of the wake during sedimentation. Using numerical data from a finite element simulation of a sedimenting particle, we first solve for the order of the derivative that returns the correct decay of the history force. We then propose a relatively simple expression for the history force that is a function of the Reynolds number and particle-to-fluid density ratio. The new history drag expression correlates very well (R²>0.99) with the numerical data for terminal Reynolds numbers ranging from 2.5 to 20, and for particle-to-fluid density ratios of interest in practice (1<β<10).     

可压缩涡中的激光传播

采用一种二维弱可压缩性的轴对称的涡模型,研究单个涡和光波阵面的相互干扰.对于低能量激光,在近场采用几何光学的分析方法.计算受干扰波阵面的光程差以及抖动角,确定通过涡的低密度区后会加速波阵面的变形,单体涡对光束有散焦作用.计算化学氧碘激光(COIL)通过涡之后的斯特列尔比,证明涡强对斯特列尔比有重要的影响.     

Impact of trailing wake drag on the statistical properties and dynamics of finite-sized particle in turbulence

We study by means of an Eulerian-Lagrangian model the statistical properties of velocity and acceleration of a neutrally-buoyant finite-sized particle in a turbulent flow statistically homogeneous and isotropic. The particle equation of motion, besides added mass and steady Stokes drag, keeps into account the unsteady Stokes drag force-known as Basset-Boussinesq history force-and the non-Stokesian drag based on Schiller-Naumann parametrization, together with the finite-size Faxén corrections. We focus on the case of flow at low Taylor-Reynolds number, Re_λ?31, for which fully resolved numerical data which can be taken as a reference are available [Homann H., Bec J. Finite-size effects in the dynamics of neutrally buoyant particles in turbulent flow. J Fluid Mech 651 (2010) 81-91]. Remarkably, we show that while drag forces have always minor effects on the acceleration statistics, their role is important on the velocity behavior. We propose also that the scaling relations for the particle velocity variance as a function of its size, which have been first detected in fully resolved simulations, does not originate from inertial-scale properties of the background turbulent flow but it is likely to arise from the non-Stokesian component of the drag produced by the wake behind the particle. Furthermore, by means of comparison with fully resolved simulations, we show that the Faxén correction to the added mass has a dominant role in the particle acceleration statistics even for particles whose size attains the integral scale.     

On numerical modeling of the dynamics of turbulent wake behind a towed body in linearly stratified medium

Two numerical models of the dynamics of a turbulent wake behind a towed body in a linearly stratified medium are compared, namely, the model based on direct numerical integration of Navier-Stokes equations in the Oberbeck-Boussinesq approximation and the mathematical model with applying a semiempirical turbulence model of the second order. The calculation results of the two models are similar to the known experimental data and are in good agreement.     

The onset of chaos in the wake of an oscillating cylinder: Experiment and the dynamics of the circle map

This paper deals with a comparison between experimental observations in a low-Reynolds-number wake behind an oscillating cylinder and the universal properties of a sine circle map. When the limit cycle due to the natural vortex shedding in the wake is modulated at a second frequency by oscillating the cylinder transversely, one obtains in phase space a flow on a two torus. The nonlinear interaction between the two oscillators results in Arnol’d tongues due to phase locking, the devil’s staircase along the critical line, and a transition from order to chaosvia the quasiperiodic route. The sine circle map describes these features adequately. A comparison between the experiment and the theory is made in terms of multifractal formalism and trajectory scaling function.     

The dynamics of charged particles in the near wake of a verynegatively charged body-laboratory experiment and numerical simulation

A numerical simulation that is cylindrical in configuration space and 3-D (v_x, v_y, v_z) in velocity space has been initiated to test a model for the near-wake dynamics of a very negatively charged body, with reference to the plasma environment around spacecraft. The simulation parameters were closely matched to those of a laboratory experiment so that the results may be compared directly. It was found from the laboratory study that the electrons and ions can display different temporal features in the filling-in of the wake; and that they both can be found in the very near-wake region (within one body diameter) of an object with a highly negative body potential. It was also found that the temperature of the electrons in the very near wake could be somewhat colder than the ambient value, suggesting the possibility of a filtering mechanism being operative there. The simulation results to date largely corroborate the density findings in terms of the presence of an enhancement for both ions and electrons and in its location     

Thermomechanically Excited Vortical Flow in a Hybrid-Oriented Nematic Channel

Physics of the Solid State - In this paper, we described numerically several scenarios of formation of vortex flows (VF) in microsized hybrid-oriented liquid crystal (HOLC) channels with...     

强磁场与涡旋场中的夸克胶子物质

相对论重离子碰撞可以产生高温的夸克胶子物质,同时也产生极强的电磁场和流体涡旋。在强电磁场和涡旋场中的夸克胶子物质呈现出新奇的宏观量子现象,比如手征磁效应、手征涡效应、手征分离效应、手征电分离效应、自旋极化现象等。它们一方面给我们提供了可以探测高温下量子色动力学的非平庸规范场拓扑结构、强相互作用的宇称破坏、夸克胶子物质中的自旋动力学等的实验手段,另一方面也与物理学其他分支,比如粒子物理、凝聚态物理、天体物理、冷原子物理等发生紧密联系,形成新的交叉研究领域。本文旨在对这些宏观量子现象的产生机制以及它们在相对论重离子碰撞中的探测等做一回顾和展望。特别地,我们揭示出重离子碰撞的磁场强度可以达到$10^{18}\sim 10^{20}$ G,流体涡旋可以达到$10^{22}$ s–1;这是我们已知当前宇宙中最强的磁场和流体涡旋。我们定量地对同量素碰撞实验做了分析,发现即便背景比例达到93%以上,当前的同量素碰撞实验仍然可在大约$3\sigma$的显著性水平上判断是否有手征磁效应的发生。我们系统地给出了满足因果律的自旋流体力学方程,并推导了其中的集体激发模式,这将有助于理解超子自旋极化中出现的符号问题。     

Status of experiments probing the dynamics of water in confinement

In many relevant situations, water is not in its bulk form but is instead attached to some substrates or filling some cavities. We shall call water in the latter environment confined or interfacial water as opposed to bulk water. This confined water is essential for the stability and function of biological macromolecules. In this review paper, we present the more recent up to date account of the dynamics of confined water as compared with that of bulk water. Various techniques are used to study the dynamics of confined water. Among them, quasi-elastic and inelastic neutron scattering is a powerful tool to study translational and rotational diffusion as well as vibrational density of states of confined water. Various examples involving water confined in porous media, adsorbed on surface of ionic crystals, in the presence of organic solutes and at the surface of biological molecules are presented. The combined effects of the hydration level and the temperature on the retardation of the water molecules motions are discussed on the basis of phenomenological models as well as of power law fits based on the Mode Coupling Theory.Received: 1 January 2003, Published online: 8 October 2003PACS: 61.12.Ex Neutron scattering (including small-angle scattering) - 66.30.Pa Transport properties of condensed matter (nonelectronic): Diffusion in nanoscale solids     

Collective dynamics of supercritical water

Inelastic X-ray scattering experiments on sub- and supercritical water were performed to investigate collective dynamics of this unique solvent. Analysis within a generalized Langevin formalism shows that the positive dispersion of the sound velocity, as compared to the hydrodynamic value, first decreases (1.0<ρ<0.8 g cm⁻³) at all measured momentum transfers (1.3-10.7 nm⁻¹), and then increases (0.7<ρ<0.26 g cm⁻³) again only at higher momentum transfers. We suggest the initial decrease is due to approaching the percolation limit in the number of hydrogen bonds, and the subsequent increase is due to the formation of rigid dimers in sub- and supercritical water.