Sloping convection: A paradigm for large-scale waves and eddies in planetary atmospheres?

In laboratory studies and associated theoretical and numerical work covering a very wide range of conditions (as specified by the key dimensionless parameters of the systems used) the phenomenon of sloping convection in rotating fluids can manifest itself in one of several spatial forms (waves, closed eddies, and combinations thereof), but all with strong local gradients (fronts, jet streams) and exhibiting various types of temporal behavior [steady, periodic vacillation, aperiodic (geostrophic) turbulence]. These general properties were first discovered in cylindrical (annular) systems, but they do not depend critically on geometry; differences between spherical and cylindrical systems are largely to be found in quantitative details. In all cases, the raison d'e tre of sloping convection is horizontal advective transfer, a process accompanied by upward advective heat transfer, which affects and may control vertical potential density gradients. It has been argued that sloping convection is the basic dynamical process underlying a wide variety of large-scale flow phenomena seen in planetary atmospheres (e.g., irregular waves in the Earth's atmosphere, regular waves in the Martian atmosphere, the Jovian Great Red Spot and other long-lived eddies seen in the atmospheres of the giant planets). In this review the extent to which this paradigm is upheld in the atmospheres of the major planets by recent work is discussed.     

On thermal convection in slowly rotating systems

The dynamical properties of convection patterns in a fluid layer heated from below and rotating slowly about a horizontal axis are reviewed. Applications to the equatorial regions of planetary and stellar atmospheres are emphasized. Attention is drawn to the wavelike drift of hexagonal convection cells in the azimuthal direction and to the mean flow generated by all convection patterns except for rolls aligned with the axis of rotation.     

Hagen-Poiseuille-Strömung in wandstabilisierten zylindersymmetrischen Lichtbögen

The purpose of this paper is to examine the properties and parameter dependences of the electrical, thermal, dynamical and radiation quantities of a Hagen-Poiseuille flow in a cylindrical wallstabilized electrical arc. The basic equations are derived from the single fluid model of plasma physics taking into account the special arc conditions. For this flow it is outlined, that the temperature distribution and hence the electrical and radiation quantities do not depend upon the dynamical entities in the considered parameter region. The determination of these functions can be performed in the same way, which is demonstrated for the electrical arc without convection in a previous paper. Knowing the temperature distribution it is possible to calculate the dynamical quantities, which are modified by the temperature field of the arc contrary to the isothermal flow. Corresponding to this they have different parameter dependences as shown by analytical and numerical treatment for a nitrogen and an argon arc.     

Thermal and inertial modes of convection in a rapidly rotating annulus

The nature of the primary instabilities that arise in a fluid contained in a fast rotating cylindrical annulus with slightly inclined plane top and bottom boundaries, radial gravity, and internal heating is numerically analyzed. It is shown that for moderate and high Prandtl numbers, the onset of convection is described by a competition of azimuthal thermal modes with different radial structure, which dominate in different regions of the parameter space. By the combined effect of the inclined ends and rotation, there are modes that are attached to the heated wall and slanted to the prograde direction of rotation, and others which are straight and fill the convective layer. Nevertheless, for very small Prandtl numbers the velocity field of the dominant modes corresponds essentially to the inertial solution of the Poincare equation, and the temperature perturbation is forced by this velocity field. In addition, a detailed exploration of the critical Rayleigh numbers and precession frequencies of the convective modes versus the radius ratio and the Coriolis parameter, for different Prandtl numbers, is presented.     

Effectiveness of stirring measures in an axisymmetric rotating annulus flow

Lagrangian stirring in a thermally driven rotating annulus is investigated numerically using a Navier-Stokes model and a second order Runge-Kutta integration routine. The stirring properties are investigated using finite scale Lyapunov exponents, Lagrangian coherent structures and a leaking method. The ability of these measures to identify transport barriers, regions of well and poorly stirred flow, and stable and unstable manifolds is investigated, as well as the stirring properties of the annulus flow. It is found that finite scale Lyapunov exponents characterise the stirring properties of flows occurring in the rotating annulus more efficiently than the leaking method or Lagrangian coherent structures. The strength of the stirring varies monotonically with thermal forcing amplitude, but non-monotonically with forcing frequency. The flows investigated are axisymmetric (i.e. two dimensional) and time dependent.     

Phase space structure and anomalous diffusion in a rotational fluid experiment

The transport of passive scalars is considered in a model of rotating annulus experiments. The system has a chain of vortices and a jet, separated by a stochastic layer. For special values of the control parameters, the boundary of the stochastic layer can contain self-similar structures of islands with regular trajectories. Two such values are identified, with the structure being on the jet boundary and on the vortex boundary, respectively. The transport properties for both cases were studied by high-precision direct numerical integration of the equations of motion. The presence of such structures is found to significantly affect the statistical properties of the trajectories and the transport exponent. The results of the computations are compared with various theoretical models of anomalous diffusion. The particle behavior was found to depend significantly on the time scale, with different theories being applicable on different time intervals. Some regimes do not match any of the existing theories. (c) 2000 American Institute of Physics.     

Natural convection of water-copper nanoliquids confined in low-porosity cylindrical annuli

Natural convection in cylindrical porous annuli saturated by a nanoliquid whose inner and outer vertical radial walls are respectively subjected to uniform heat and mass influxes and out fluxes is studied analytically using the modified Buongiorno-Darcy model (MBDM) and the Oseen-linearization technique. Nanoliquid-saturated porous medium made up of water as base liquid, copper nanoparticles of five different shapes, viz., spheres, bricks, cylinders, platelets and blades, and glass balls porous material is considered as working medium for investigation. The thermophysical properties of nanoliquid -saturated porous medium is modeled using phenomenological laws and mixture theory. The effect of various parameters and individual effects of five different shapes of copper nanoparticles on velocity, temperature and heat transport are found. From the study, it is clear that the addition of a dilute concentration of nanoparticles increases the effective thermal conductivity of the system and thereby increases the velocity and the heat transport, and decreases the temperature. In other words, the heat transport is more in the case of heat and mass driven convection compared to purely heat-driven convection. Among the five different shapes of nanoparticles, blade-shaped nanoparticles facilitate the transport of maximum temperature compared to all other shapes. Maximum heat transport is achieved in a shallow cylindrical annulus compared to square and tall circular annuli. The increase of the inner solid cylinder’s radius is to decrease heat transport. The results of the KVL single-phase model are obtained from the present study by setting to zero the value of the nanoparticles’ concentration Rayleigh number. Also, neglecting the curvature effect in the present problem, we obtain the results of the rectangular enclosure problem.     

Impacts of external electric fields on the permeation of glycerol and water molecules through aquaglyceroporin-7: molecular dynamics simulation approach

The European Physical Journal E - The current research numerically investigates the Marangoni convection in a cylindrical annulus filled with hybrid nanofluid saturated porous media. The interior...     

柱状固体复合结构对斜入射超声波的散射

较详细阐述了三层柱状固体复合结构对斜入射超声波的散射理论.厚度远小于声波波长和内层半径的中间圆环可模拟为内外层媒质之间的界面薄层.将声波斜入射时中间国环层力学量的传递矩阵作线性近似展开,我们首次建立了描述界面薄层的三维弹簧物理模型,由此进一步分析了固体界面处的声学边界条件.利用弹簧模型,我们最后从数值上研究了玻璃纤维/铝基复合结构中界面薄层力学参量的变化对斜入射超声散射截面积的影响.     

Gravitational Jaynes–Cummings model beyond the rotating wave approximation

In this paper, the quantum properties of a two-level atom and the cavity-field in the Jaynes?CCummings model with the gravity beyond the rotating wave approximation are investigated. For this purpose, by solving the Schr?dinger equation in the interaction picture, the evolving state of the system is found by which the influence of the counter-rotating terms on the dynamical behaviour of atomic population inversion and the probability distribution of the cavity-field as quantum properties is explored. The results in the atom?Cfield system beyond the rotating wave approximation with the gravity show that the quantum properties are not completely suppressed under certain conditions.     

Modeling of Ice-Water Phase Change in Horizontal Annulus Using Modified Enthalpy Method

Phase change in ice-water systems in the geometry of horizontal cylindrical annulus with constant inner wall temperature and adiabatic outer wall is modeled with an enthalpy-based mixture model. Solidification and melting phenomena under different temperature conditions are analyzed through a sequence of numerical calculations. In the case of freezing of water, the importance of convection and conduction as well as the influence of cold pipe temperature on time for the complete solidification is examined. As for the case of melting of ice, the influence of the inner pipe wall temperature on the shape of the ice-water interface, the flow and temperature fields in the liquid, the heat transfer coefficients and the rate of melting are analyzed. The results of numerical calculations point to good qualitative agreement with the available experimental and other numerical results.     

Theoretical study of the decaying convective turbulence in a shear-buoyancy PBL

The derivation of a theoretical model for the decaying convective turbulence in a shear-buoyancy planetary boundary layer is considered. The model is based on the dynamical equation for the energy density spectrum in which the buoyancy, mechanical and inertial transfer terms are retained. The parameterization for the buoyancy and mechanical terms is provided by the flux Richardson number. Regarding the inertial term an approach employing Heisenberg’s spectral transfer theory is used to describe the turbulence friction, caused by small eddies, responsible for the energy dissipation of the large eddies. Therefore, a novelty in this study is to utilize the Adomian decomposition method to solve directly without linearization the energy density spectrum equation, with this the nonlinear nature of the problem is preserved. Therefore, the errors found are only due to the parameterization used. Comparison of the theoretical model is performed against large-eddy simulation data for a decaying convective turbulence in a shear-buoyancy planetary boundary layer. The results show that the existence of a mechanical turbulent driving mechanism reduces in an accentuated way the energy density spectrum and turbulent kinetic energy decay generated by the decaying convective production in a shear-buoyancy planetary boundary layer.     

Infrared remote sensing of planetary atmospheres

Infrared remote sensing is a powerful tool for studying the chemical composition and the thermal structure of planetary atmospheres. Infrared spectra, in particular, are used to derive molecular abundances and to infer elemental and isotopic ratios, which allow to constrain theoretical models of the formation and early evolution of the solar system, as well as the history of planetary atmospheres. Infrared imaging and spectroscopy have been performed from the ground but also from space planetary missions (Mariner 9 on Mars, Voyager on the giant planets, Galileo on Jupiter), and from the ISO Earth-orbiting infrared satellite. In the forthcoming decade, the Cassini mission will explore the Saturn system. Planetary exploration from Earth orbit will be performed by the FIRST and NGST space observatories.     

大尺度螺旋孤子实验

通过大型流体动力学转盘实验,证实了自然界中以台风为代表的大尺度涡旋运动形态具有孤子特性,建议用“螺旋孤子”来刻划这类运动形态 关键词：     

Speedup of self-propelled helical swimmers in a long cylindrical pipe

Pipe-like confinements are ubiquitously encountered by microswimmers.Here we systematically study the ratio of the speeds of a force-and torque-free microswimmer swimming in the center of a cylindrical pipe to its speed in an unbounded fluid(speed ratio).Inspired by E.coli,the model swimmer consists of a cylindrical head and a double-helical tail connected to the head by a rotating virtual motor.The numerical simulation shows that depending on swimmer geometry,confinements can enhance or hinder the swimming speed,which is verified by Reynolds number matched experiments.We further developed a reduced model.The model shows that the swimmer with a moderately long,slender head and a moderately long tail experiences the greatest speed enhancement,whereas the theoretical speed ratio has no upper limit.The properties of the virtual motor also affect the speed ratio,namely,the constant-frequency motor generates a greater speed ratio compared to the constant-torque motor.     

Turbulent structures in cylindrical density currents in a rotating frame of reference

Gravity currents are flows generated by the action of gravity on fluids with different densities. In some geophysical applications, modeling such flows makes it necessary to account for rotating effects, modifying the dynamics of the flow. While previous works on rotating stratified flows focused on currents of large Coriolis number, the present work focuses on flows with small Coriolis numbers (i.e. moderate-to-large Rossby numbers). In this work, cylindrical rotating gravity currents are investigated by means of highly resolved simulations. A brief analysis of the mean flow evolution to the final state is presented to provide a complete picture of the flow dynamics. The numerical results, showing the well-known oscillatory behavior of the flow (inertial waves) and a final state lens shape (geostrophic adjustment), are in good agreement with experimental observations and theoretical models. The turbulent structures in the flow are visualized and described using, among others, a stereoscopic visualization and videos as supplementary material. In particular, the structure of the lobes and clefts at the front of the current is presented in association to local turbulent structures. In rotating gravity currents, the vortices observed at the lobes front are not of hairpin type but are rather of Kelvin-Helmholtz type.     

Air flow control around a cylindrical model induced by a rotating electric arc discharge in an external magnetic field. Part I

The structure and dynamics of a near-wall gas flow produced by a rotating electric arc discharge in an external magnetic field around a cylindrical model without an incoming flow has been investigated. The electric arc on the model has been produced by a combined electric discharge (low-current rf discharge + high-current pulse-periodic discharge). Permanent magnets with induction B ≈ 0.1 T have been placed inside the cylindrical models. Ring electrodes are arranged on the surface of the model. The structure and dynamics of the near-wall gas flow around the cylindrical model have been investigated using high-speed photography, as well as the shadowgraph and particle image velocimetry (PIV) methods.     

The Perturbation Effect of Rotating Solar Polytropic Model on the Variation of Planetary Orbital Elements

In this paper the author examines the perturbation effect of rotating solar polytropic model on the variation of planetary orbital elements by the method of general perturbation in celestial mechanics and the polytropic model ofgaseous star in astrophysics. The perturbation variables of planetary orbital elements caused by the rotation, oblateness and central density of the sun for the polytropic index n = 3 are derived. The result shows clearly that the periodic perturbation effects are the orbital elements of all and the secular perturbation effects are the variation of the longitudes of perihelion, the ascending node and the mean anomaly of epoch. Finally, the author applies the obtained theoretical results to a calculation of the variation of orbital elements of four planets. The numerical results are given in Table 1.