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We present a novel method for the simulation of the aerodynamic admittance in bluff body aerodynamics. The method introduces a model for describing oncoming turbulence in two-dimensional discrete vortex method simulations by seeding the upstream flow with vortex particles. The turbulence is generated prior to the simulations and is based on analytic spectral densities of the atmospheric turbulence and a coherence function defining the spatial correlation of the flow. The method is validated by simulating the turbulent flow past a flat plate and past the Great Belt East bridge. The results are generally found in good agreement with the potential flow solution due to Liepmann.

Turbulent mixing layer flow in a vertical water channel was experimentally investigated by particle image velocimetry (PIV). The mixing layer is produced by a specially designed insert plate placed in the channel with a low- and high-speed side velocity ratio of 0.25. The Reynolds number based on the velocity difference of two streams and the spanwise vorticity thickness at the place where the mixing layer start merging ranges from 2184 to 14 672. The results show that there are large coherent vortex structures near the centreline of the mixing layer. Both instantaneous kinetic energy and spanwise vorticity always concentrate at the location where the coherent structures connect or meet each other. The normalised dimensionless Reynolds stresses and average spanwise vorticity show self-similar, respectively, under different Reynolds numbers at the same cross-section in the down streamwise direction. Every component of Reynolds stresses increases but the vorticity decreases with the downstream distance. For all Reynolds number, the peak values of mean vorticity in the streamwise direction appear the same decay speed. The splitter plane wake causes a negative peak of the mean vorticity where the mixing layer merges. The negative peak values of vorticity increase with the Reynolds number. The dimensionless negative peak values decrease exponentially with Reynolds number and reach a constant when the Reynolds number is large enough. Le debit de couche de melange turbulent dans une conduite d'eau verticale a ete analyse de facon experimentale par velocimetrie par images de particules (PIV). La couche de melange est produite a l'aide d'une plaque d'insertion de conception particuliere placee dans le conduit avec un rapport de vitesse laterale basse et elevee de 0,25. Le nombre de Reynolds fonde sur la difference de vitesse de deux courants et l'epaisseur du tourbillon dans le sens de l'envergure a l'endroit ou la couche de melange commence a fusionner se situe entre 2,184∼14,672. Les resultats indiquent qu'il existe de grandes nappes de tourbillons coherentes pres de la ligne centrale de la couche de melange. A la fois l'energie cinetique instantanee et le tourbillon dans le sens de l'envergure se concentrent toujours a l'endroit ou les nappes coherentes se rencontrent. Les tensions de Reynolds normalisees adimensionnelles et le tourbillon dans le sens de l'envergure moyen demontrent qu'ils sont autosimilaires respectivement sous differents nombres de Reynolds a la meme section transversale en aval. Chaque element des tensions de Reynolds s'accroit, mais le tourbillon diminue avec la distance en aval. Pour tout nombre de Reynolds, les valeurs de crete du tourbillon moyen dans la direction du flux semblent etre de la meme vitesse de desintegration. Le sillage plan de separation cause une crete negative de tourbillon moyen lorsque la couche de melange est fusionnee. Les valeurs de crete negatives du tourbillon augmentent avec le nombre de Reynolds. Les valeurs de crete negatives adimensionnelles diminuent de facon exponentielle avec le nombre de Reynolds et atteignent une constante lorsque le nombre de Reynolds est suffisamment grand. Can. J. Chem. Eng. © 2010 Canadian Society for Chemical Engineering

The effects of pinning between fluxoids and vortices in the core of a neutron star, on the dynamics of the core neutron superfluid are considered. The pinning impedes, but does not absolutely block, any radial as well as {\em azimuthal} motion of the neutron vortices with respect to the lattice of fluxoids. The time scale for the coupling of rotation of the core superfluid to the rest of the star is calculated, allowing for the effect of the finite frictional force on the neutron vortices due to their pinning with the fluxoids. This turns out to be the dominant mechanism for the coupling of the core of a neutron star to its crust, as compared to the role of electron scattering, for most cases of interest. Furthermore, different behaviors for the post-glitch response of the core superfluid are distinguished that might be tested against the relevant observational data. Also, a conceptually important case (and controversial too, in the earlier studies on the role of the crustal superfluid) is realized where a superfluid may remain decoupled in spite of an spinning up of its vortices., Accepted for publication in ApJ

We investigate the vortex states interacting with a square array of pinning sites in a superconducting sample by using a molecular dynamics approach. An improved potential is used to model the interaction between the vortices and the pinning sites. We found several shell-type structures depending on the numbers of the vortices and pinning sites. We show that the vorticity increases with increasing of magnetic field and (meta)stable vortex shells occur due to the changes in the vorticity. We deduce that the large pinning sizes are essential to obtain higher order vortex shells. Our results are compared with those obtained from the numerical and experimental studies.

Directed transport of vortices in a Josephson junction network (JJN) with structural disorder is studied using a numerical simulation. Using spatiotemporal modulation of driving currents, the directed transport of vortices occurs even in the presence of disorder under certain conditions. From the analyses of the current–voltage and local voltage characteristics, it is found that the collective motion of vortices has an importance for the occurrence of directed transport.

We present a novel method of constructing streamlines to derive wind speeds within jovian vortices and demonstrate its application to Oval BA for 2001 pre-reddened Cassini flyby data, 2007 post-reddened New Horizons flyby data, and 1998 Galileo data of precursor Oval DE. Our method, while automated, attempts to combine the advantages of both automated and manual cloud tracking methods. The southern maximum wind speed of Oval BA does not show significant changes between these data sets to within our measurement uncertainty. The northern maximum dries appear to have increased in strength during this time interval, tvhich likely correlates with the oval's return to a symmetric shape. We demonstrate how the use of closed streamlines can provide measurements of vorticity averaged over the encircled area with no a priori assumptions concerning oval shape. We find increased averaged interior vorticity between pre- and post-reddened Oval BA, with the precursor Oval DE occupying a middle value of vorticity between these two.

We study the distinction between giant vortex states and multivortex states in a thin mesoscopic superconducting square by using the temperature dependence of the vortex expulsion fields. We find that the results agree well with those obtained from the multiple-small-tunnel-junction method, indicating that the distinction by the temperature dependence of the vortex expulsion fields is applicable to superconducting squares.

The dye visualization experiments show that a dual leading-edge vortex (LEV) structure exists on the suction side of a simplified butterfly model of Papilio ulysses at α = 8°−12°. Furthermore, the results of particle image velocimetry (PIV) measurement indicate that the axial velocity of the primary (outer) vortex core reaches the lower extreme value while a transition from a “wake-like” to a “jet-like” axial velocity profile occurs. The work reveals for the first time the existence of dual LEV structure on the butterfly-like forward-sweep wing configuration.

The discovery of superconductivity in MgB2 and, more recently, in iron pnictides, revived the interest in two-component and other exotic superconductors, including in the field of vortex matter, as was shown recently by the discovery of “type 1.5” superconductivity. However, even some “older” exotic cuprates grown by high-pressure techniques showed interesting anomalies related to the interplay between Josephson and magnetic coupling and/or two-gap superconductivity. Here, we will present two such examples of exotic vortex matter: magnetically-coupled pancake-vortex molecules in super-multilayered cuprates, and vortex molecules composed of fractional flux quanta glued by an interband phase difference soliton, and will discuss the major differences between MgB2 and such multilayer cuprates in terms of the relative strength of the interband interaction and, respectively, in terms of the coherence and penetration lengths.

We have investigated the distribution of external current injected from superconducting leads into mesoscopic samples using time dependent Ginzburg-Landau theory. In particular, we have taken account of the current and field variation in the thickness direction. We have performed numerical simulations for the sample composed of two rectangular solids connected by two bridges. We have observed “switching” like behavior in the current distribution at the bridges, which corresponds to the change between vortex penetration and expulsion. This switching like behavior, as well as the magnitude of the currents, depends on the sample thickness in the direction of the external field.

Larval transport from distant populations is essential for maintenance and renewal of populations in patchy and disturbed ecosystems such as deep-sea hydrothermal vents. We use quasi-geostrophic modeling to consider the potential for long-distance dispersal of hydrothermal vent larvae in mesoscale eddies interacting with the northern East Pacific Rise. Modeled eddy dynamics were similar to the observed propagation dynamics of Tehuantepec eddies, including their ability to cross the ridge. Simulated surface anticyclones were associated with coherent cyclones in the deep layer with relatively strong current velocities that could significantly increase the dispersal potential of passive particles. Eddy interactions with ridge topography further enhanced tracer dispersal along the ridge axis through shearing and elongation of the eddy core. Simulations suggest that the passage of an eddy would result in local loss from the vent field and aggregate transport with potential enhancement of dispersal between vent fields separated by up to 270 km. Based on the latitude at which most Tehuantepec eddies cross the ridge, eddy-induced flows would enhance connectivity between the 13°N, 11°N, and 9°N vent fields along the East Pacific Rise asymmetrically with higher transport from northern vent fields to southern vent fields.

In spite of a low circumferential Mach number the sound of isolated centrifugal fan impellers is sometimes dominated by distinctive tones at blade passing frequency (BPF) and integer multiples. This paper reports on an experimental and numerical investigation intended to unveil the tone generating mechanism. The sound spectra from three impellers operating at a large range of speed were measured and decomposed into Strouhal and Helmholtz number dependent functions. This led to the preliminary conclusion that the BPF related tones are exclusively flow-induced. Based on hot-wire and blade pressure fluctuation measurements and a subsequent correlation analysis, coherent flow structures different from those associated with the principal azimuthal flow pattern due to the blades were detected. Eventually a numerical three-dimensional unsteady flow simulation revealed an inlet vortex. It takes on a helical form, with the vortex core slowly varying its position with respect to the impeller center. As the blades cut through that quasi-stationary helical vortex they encounter blade force fluctuations, producing the BPF tones. Slow spin of the vortex core and slow variation of vortex strength were identified as the reasons for amplitude modulation of the BPF tone.

A swirl flow is achieved in a bed of solids by passing air through multiple fluid inlets, which are tangentially located at the base of a flat-based circular column. The minimum superficial velocities needed to achieve swirling of the bed are measured experimentally under varied conditions. An empirical correlation for the minimum swirl velocity has been proposed. The results indicate that a stable swirling regime operation of the bed is possible. There exists an upper limit of static bed depth beyond which stable swirling of entire bed is not possible. The minimum swirl velocities are found to be 1.2–1.3 times the minimum fluidization velocities predicted for conventional fluidized beds.

We examine jamming and ratchet effects for vortex matter in superconductors with asymmetric funnel geometries. We show that the vortex–vortex interactions can induce a clogging or jamming effect where it becomes increasingly difficult for the vortices to move through the system. We also find that commensurability effects can arise when certain vortex configurations form highly symmetrical structures in the funnel plaquettes. Due to the asymmetry, the critical currents are different for driving in different directions, leading to a diode effect. We also discuss other possible geometries and approaches that could be used to explore jamming in vortex matter, such as an analog to a granular hopper and a single driven vortex probe moving through an array of other vortices.

We have observed vortex penetration into Nb thin films with square arrays of square holes with variable sizes and lattice constants. We find that when the lattice spacing is large and the width of superconducting line is narrow, vortices penetrate diagonally rather than parallel to the nearest neighbor direction. This phenomenon is also confirmed in NbTiN samples with the same geometry. We also confirm that the direction of edge relative to that of hole array is not relevant. Possible origin of such a preferential penetration is proposed.

Traffic-signal-support structures with cantilevered mast arms are known to exhibit large-amplitude vibrations under certain wind conditions. Previous investigations of the problematic vibrations have primarily focused on the aerodynamics of the signal heads of various configurations. Based on full-scale measurement of a traffic-signal-support structure, the role of the cantilevered mast arm in the aeroelastic vibrations is studied. Contrary to previous reports that the vibrations are due to galloping of the traffic signals, this study reveals that the aeroelastic interaction between the wind and the mast arm is critical in the excitation mechanism of the vibrations. Two types of excitation mechanisms, vortex-shedding at low wind speeds and buffeting at high wind speeds, were identified.

The rotating waves within a hollow vortex core (polygonal patterns) are generated under shallow water conditions inside a cylindrical tank by a revolving disk at its bottom. We previously reported some basic features of these polygonal patterns during transition and at the equilibrium states. The present paper includes a more comprehensive investigation into the transition process of these polygonal patterns and expands the recent partial results that have been previously reported. We show that the parent wave (or the N-gon pattern) to disk frequencies ratio is around one-third (1/3) regardless of the flow conditions. A detailed insight into the transition process from the parent wave N-gon to daughter wave (N + 1)-gon is provided, which consists of two regimes, quasi-periodic and synchronized. Based on these observations, we explained the shrinking of the disk speed subintervals over which the N-gon patterns occur, when N increases.

The three-dimensional axisymmetric wind field structure of the violent Spencer, South Dakota, 1998 tornado was analyzed using the ground-based velocity track display (GBVTD) method. Data from a Doppler on Wheels mobile radar, collected at very close range to the tornado, were used to conduct the GBVTD calculations at a very fine (16 m) resolution. The analysis revealed a two-cell vortex with a very strong axial downdraft throughout the observation period, radial inflow jets preceding intensification and a decrease in inflow preceding weakening, swirl ratio values consistent with observed multiple vortex structure, and other features of the vortex.

Geostrophic eddies control the meridional mixing of heat, carbon, and other climatically important tracers in the Southern Ocean. The rate of eddy mixing is typically quantified through an eddy diffusivity. There is an ongoing debate as to whether eddy mixing in enhanced in the core of the Antarctic Circumpolar Current or on its flanks. A simple expression is derived that predicts the rate of eddy mixing, that is, the eddy diffusivity, as a function of eddy and mean current statistics. This novel expression predicts suppression of the cross-jet eddy diffusivity in the core of the Antarctic Circumpolar Current, despite enhanced values of eddy kinetic energy. The expression is qualitatively and quantitatively validated by independent estimates of eddy mixing from altimetry observations. This work suggests that the meridional eddy diffusivity across the Antarctic Circumpolar Current is weaker than presently assumed because of the suppression of eddy mixing by the strong zonal current.

The meridional shift of the Kuroshio Extension to decadal wind variations is examined by analyzing the hindcast simulation of a high-resolution ( 1 / 12 ∘ × 1 / 12 ∘ ) North Pacific ocean general circulation model (OGCM) and by conducting a series of idealized OGCM experiments. The meridional shift of the Kuroshio Extension in the hindcast is consistent with observations and former studies. Using a series of sensitivity experiments in idealized settings, the following possible mechanism for this shift is proposed. The baroclinic Rossby waves that arise in the northern half of the subtropical gyre cannot directly enter the Kuroshio–Oyashio Extension region due to the strong Kuroshio Extension jet. When the Rossby waves accompanying the negative (positive) sea-surface height anomalies propagate westward and reach the region to the east of the recirculation gyre, the difference in thermocline depth between the recirculation gyre and the region to its east becomes larger (smaller), resulting in stronger (weaker) baroclinic instabilities. These stronger (weaker) instabilities cause a shallower (deeper) thermocline in the recirculation gyre. To compensate for this shrinking (stretching), the recirculation gyre migrates southward (northward), leading to the southward (northward) shift of the Kuroshio Extension.

Satellite altimeter sea-surface height (SSH) data of the past 16 years are used to investigate the decadal changes of the Kuroshio Extension (KE) system that oscillated between a stable and an unstable dynamic state. During the stable state of 10/1992–06/1995 and 01/2002–12/2004, the KE jet was intense and had a northerly zonal mean path and a well-defined southern recirculation gyre. During the unstable state of 07/1995–12/2001 and 01/2005–present, the KE jet had a reduced eastward transport and a more southerly flow path. Transitions between the two dynamic states are caused by the basin-scale wind-stress curl forcing in the eastern North Pacific related to the Pacific decadal oscillations (PDOs) or the North Pacific Gyre Oscillations (NPGOs). During the positive PDO (or negative NPGO) phase, the intensified Aleutian Low generates negative SSH anomalies in the eastern North Pacific through Ekman divergence. As these wind-induced negative SSH anomalies propagate to the west as baroclinic Rossby waves, they weaken the zonal KE jet and shift its path southward. As its path is pushed southward ( ∼ 32 ∘ N ) , the deep-reaching KE jet has to ride over the shallow Shatsky Rise, generating localized disturbances that lead to their subsequent development along the KE jet west of the Shatsky Rise. The sequence opposite to that listed above occurs when the PDO (NPGO) changes to its negative (positive) phase. After the KE system transitions from a stable to unstable state, the enhanced eddy interaction is found to strengthen both the southern recirculation gyre and quasi-stationary meanders along the KE's upstream path. This nonlinear eddy interaction is important in determining the amplitude of the observed decadal KE variability.

Tensioned-web-over-slot die coating (TWOSD) takes advantage of the elastohydrodynamic interaction between the curved web under tension and the coating liquid to sustain a very small coating gap that enables ultra thin coating at relatively high speed. When the product requires two liquid layers, dual slot TWOSD coating can be used to coat those layers simultaneously. In this case, the liquid pressure along the coating bead sets not only the web configuration and meniscus locations but also the interlayer separation point. An easy way to control the pressure distribution is through the die lip geometry. Here, we analyze the effect of four different die lip geometric parameters, e.g. the downstream lip radius, the mid lip radius, the downstream lip offset and the mid lip apex point, on the coating window of the dual slot TWOSD coating. Using the model proposed by Nam and Carvalho (2009c) and a direct tracking of flow features, the boundaries of the vortex-free operating window, area inside the parameter spaces that ensure a uniform coating without vortex inside the flow, were obtained and compared for each die lip configuration. We found that the mid lip radius is one of the important parameters to control the location of the upstream meniscus. Also the location of the interlayer separation point can be controlled by the lip offset and location of the apex point.

Synoptic eddy–mean flow interaction has been recognized as one of the key sources for extratropical low-frequency variability. In this paper, the underlying dynamics of this interaction are examined from the perspective of a synoptic eddy-induced dynamic instability. To delineate this instability, a barotropic model is used that is linearized with respect to a stochastic basic flow prescribed with both climatologic-mean flow and synoptic eddy statistics. This linear model captures the dynamics of feedback between synoptic eddy and low-frequency flow through a dynamic closure that relates the anomalous eddy vorticity forcing to low-frequency flow anomalies. After reducing this dynamic closure to its fundamental components, this stability is elucidated with analytical results under the most idealized consideration of basic flow. It is shown that through systematic alteration of the synoptic eddy structures in the basic flow, a low-frequency planetary-scale perturbation generates anomalous eddy vorticity forcing positively proportional to the vorticity of the perturbation. Such a perturbation amplifies itself; the energy source for its growth comes from the reservoir residing in the basic synoptic eddy activity. Thus, the growth rate of the synoptic eddy-induced dynamic instability depends primarily on the kinetic energy level of the basic synoptic eddy activity. Moreover, this instability is scale selective with preference for zonal symmetric and asymmetric planetary-scale modes, whose meridional and zonal scales are roughly in the range of those of the observed leading low-frequency patterns. Analysis of this synoptic eddy-induced instability provides insight into the origin of extratropical low-frequency variability.

The tourbillon is a mechanical device that was invented to improve the precision of old-fashioned pocket watches. These devices continually rotate the escapement, balance wheel, and spring to compensate for bias due to gravity. A high-quality modern mechanical watch can achieve a precision, referred to as rate error in the horological community, of 1 s per day, while a less expensive mechanical watch may attain a precision of 5 s per day. To place these figures in perspective, the precision of an inexpensive quartz watch is less than .5 s per day. Measuring the precision of a mechanical timepiece is not quite as obvious at it may seem because the variation in watch speed depends on various factors, such as temperature and spatial orientation. Temperature compensation has been the subject of much thought and experimentation over the centuries. Consequently, the construction of a modern mechanical watch is such that, over a limited temperature range, the watch is insensitive to variations in ambient temperature. Variation in both accuracy and precision, that is, in watch speed and rate error, due to the orientation of the gravitational field is a characteristic of oldfashioned pocket watches.

Blowup ring profiles have been investigated by finding non-vortex blowup solutions of nonlinear Schrodinger equations (NLSEs) (cf. Fibich et al. (2005) [7] and Fibich et al. (2007) [8] ). However, those solutions have infinite L 2 norm, so one may not maintain the ring profile all the way up to the singularity. To find H 1 non-vortex blowup solutions with ring profiles, we study the blowup solutions of two-component systems of NLSEs with nonlinear coefficients β and ν j , j = 1 , 2 . When β 0 and ν 1 ≫ ν 2 > 0 , the two-component system can be transformed into a multi-scale system with fast and slow variables which may produce H 1 blowup solutions with non-vortex ring profiles. We use the localized energy method with symmetry reduction to construct these solutions rigorously. On the other hand, these solutions may describe steady non-vortex bright ring solitons. Various types of ring profiles including m -ring and ring–ring profiles are presented by numerical solutions.

Large Eddy Simulations are used to model a turbulent confined coannular combustor and examine the effects of swirl on the flow field and mixing. Three separate simulations with relatively high mesh resolutions and different swirl numbers have been carried out using a finite volume method on a Cartesian non-uniform structured grid. A localised dynamic Smagorinsky model is used to parameterize the sub-grid scale turbulence. The snapshots of the axial and swirl velocities and velocity vector fields show the complex flow patterns developing with increased swirl number and the rapid decay of axial momentum. Precessing vortex cores (PVC) were identified for all three cases and the mean axial velocity plots indicate that the upstream extremity of the vortex breakdown bubble shifts towards the inlet as the swirl number increases. The calculated power spectra indicate the distinct precession frequency for high swirl number. Probability density functions of axial velocity showed the changes of their distributions from approximately Gaussian to non-Gaussian with increased swirl number. The swirl has a large effect on the rate of decay of the axial velocity throughout the domain, whereas only has a significant effect on the decay of swirl velocity in the near field close to the jet inlet. The relation between swirl number and the axial extent of the recirculation zone is approximately linear. Radial plots of mean passive scalar and its variance also demonstrate an increase in the rate of mixing with increasing swirl number.

Receptivity of the two-dimensional boundary layer on a flat plate with elliptic leading edge is studied by numerical simulation. Vortical perturbations in the oncoming free stream are considered, impinging on two leading edges with different aspect ratio to identify the effect of bluntness. The relevance of the three vorticity components of natural free-stream turbulence is illuminated by considering axial, vertical and spanwise vorticity separately at different angular frequencies. The boundary layer is most receptive to zero-frequency axial vorticity, triggering a streaky pattern of alternating positive and negative streamwise disturbance velocity. This is in line with earlier numerical studies on non-modal growth of elongated structures in the Blasius boundary layer. We find that the effect of leading-edge bluntness is insignificant for axial free-stream vortices alone. On the other hand, vertical free-stream vorticity is also able to excite non-modal instability in particular at zero and low frequencies. This mechanism relies on the generation of streamwise vorticity through stretching and tilting of the vertical vortex columns at the leading edge and is significantly stronger when the leading edge is blunt. It can thus be concluded that the non-modal boundary-layer response to a free-stream turbulence field with three-dimensional vorticity is enhanced in the presence of a blunt leading edge. At high frequencies of the disturbances the boundary layer becomes receptive to spanwise free-stream vorticity, triggering Tollmien–Schlichting (T-S) modes and receptivity increases with leading-edge bluntness. The receptivity coefficients to free-stream vortices are found to be about 15% of those to sound waves reported in the literature. For the boundary layers and free-stream perturbations considered, the amplitude of the T-S waves remains small compared with the low-frequency streak amplitudes.

The region in Jupiter’s atmosphere with the highest density of anticyclonic spot-like vortices is the region known as the South South Temperate Zone (SSTZ), which is located between the eastward jet at ≈−42.9° latitude and the westward jet at ≈−39.2° latitude. We present a characterization of the spots found in this region based on ground-based and Hubble Space Telescope observations from the years 1993 to 2007. Mergers have been reported between spots in this region, similar to those observed for the White Ovals in the latitudinal domain immediately equatorward (northward). We use a multilayer model to perform numerical simulations that capture the details of a well-observed merger event involving multiple interacting vortices. We find that the vertical stratification has an important effect in the outcome of the interaction between spots. In particular it can play a determining role on whether or not a cyclone embedded between two approaching anticyclones can inhibit their merging. From our simulations we conclude that the background static stability of the atmosphere in the SSTZ is better characterized by an average value of N = 0.005 s - 1 .

The flow field in square tanks with various corner roundings is studied to investigate drain flow characteristics. An attempt is made to understand the mechanism of flow field responsible for vortex suppression by the different radius of rounding at the corner. For this purpose, flow visualization studies using particle image velocimetry are employed to determine the flow patterns in a square tank. Results are obtained for no draining and with draining experiments. The flow field is visualized both in horizontal and vertical planes. The results reveal that the secondary vortices formed at the corners are responsible for vortex suppression.

The issue of internal wave–mesoscale eddy interactions is revisited. Previous observational work identified the mesoscale eddy field as a possible source of internal wave energy. Characterization of the coupling as a viscous process provides a smaller horizontal transfer coefficient than previously obtained, with vh ≅ 50 m2 s−1 in contrast to νh ≅ 200–400 m2 s−1, and a vertical transfer coefficient bounded away from zero, with νυ + ( f 2/N 2)Kh ≅ 2.5 ± 0.3 × 10−3 m2 s−1 in contrast to νυ + ( f 2/N 2)Kh = 0 ± 2 × 10−2 m2 s−1. Current meter data from the Local Dynamics Experiment of the PolyMode field program indicate mesoscale eddy–internal wave coupling through horizontal interactions (i) is a significant sink of eddy energy and (ii) plays an O(1) role in the energy budget of the internal wave field.

A hexagonal structure has been observed at ∼76°N on Saturn since the 1980s (Godfrey, D.A. [1988]. Icarus 76, 335-356). Recent images by Cassini (Baines, K., Momary, T., Roos-Serote, M., Atreya, S., Brown, R., Buratti, B., Clark, R., Nicholson, P. [2007]. Geophys. Res. Abstr. 9, 02109; Baines, K., Momary, T., Fletcher, L., Kim, J., Showman, A., Atreya, S., Brown, R., Buratti, B., Clark, R., Nicholson, P. [2009]. Geophys. Res. Abstr. 11, 3375) have shown that the feature is still visible and largely unchanged. Its long lifespan and geometry has puzzled the planetary physics community for many years and its origin remains unclear. The measured rotation rate of the hexagon may be very close to that of the interior of the planet (Godfrey, D.A. [1990]. Science 247, 1206-1208; Caldwell, J., Hua, X., Turgeon, B., Westphal, J.A., Barnet, C.D. [1993]. Science 206, 326-329; Sánchez-Lavega, A., Lecacheux, J., Colas, F., Laques, P. [1993]. Science 260, 329-332), leading to earlier interpretations of the pattern as a stationary planetary wave, continuously forced by a nearby vortex (Allison, M., Godfrey, D.A., Beebe, R.F. [1990]. Science 247, 1061-1063). Here we present an alternative explanation, based on an analysis of both spacecraft observations of Saturn and observations from laboratory experiments where the instability of quasi-geostrophic barotropic (vertically uniform) jets and shear layers is studied. We also present results from a barotropic linear instability analysis of the saturnian zonal wind profile, which are consistent with the presence of the hexagon in the North Pole and absence of its counter-part in the South Pole. We propose that Saturn's long-lived polygonal structures correspond to wavemodes caused by the nonlinear equilibration of barotropically unstable zonal jets. © 2009 Elsevier Inc. All rights reserved.

We present a computationally efficient, adaptive solver for the solution of the Poisson and Helmholtz equation used in flow simulations in domains with combinations of unbounded and periodic directions. The method relies on using FFTs on an extended domain and it is based on the method proposed by Hockney and Eastwood for plasma simulations. The method is well-suited to problems with dynamically growing domains and in particular flow simulations using vortex particle methods. The efficiency of the method is demonstrated in simulations of trailing vortices.

This study investigates the two-dimensional flow of a solitary wave that passes over a submerged rectangular obstacle using a Lagrangian-type numerical method. The main purpose is to investigate vortex generation and evolution caused by the obstacle. The numerical method is based on the combination of vortex methods and boundary integral methods using the Helmholtz decomposition. The simulated flow pattern is compared with the experimental measurements in detail, and the overall agreement is reasonably good. A series of simulations were performed with various wave heights to study the effect of wave height on vortex generation and evolution. The relation between the vorticity field and the drag experienced by the obstacle is also discussed. In the presented cases, the effects of the generated vortices are preserved over a long period, and may cause local scouring of the foundation at the lee side of the obstacle. The deformation of the solitary wave is not much affected by the presence of the vortices, but the drag is significantly affected by the vorticity field. An almost linear relationship between the Reynolds number and the maximum magnitude of the drag (positive and negative) is observed.

The velocity field around a zigzagging ascent single bubble has a wide dynamic range. It is hard to precisely measure such velocity field via conventional PIV. In this study, to overcome this difficulty the authors employed recursive cross-correlation algorithm and a high-speed video camera. The analysis code of a newly developed PIV system showed a high performance in measuring velocities of a wide dynamic range. At first, the authors demonstrate the performance of the recursive cross-correlation PIV algorithm as compared with the results obtained by conventional PIV algorithm using the standard PIV images with a wide dynamic range presented by The Visualization Society of Japan. At second, the system was applied to the simultaneous measurement of the surrounding liquid motion (i.e. liquid-phase velocities) and surface motion of a single bubble zigzagging upward in purified water and contaminated water. At third, surfactant effects on the surrounding liquid motion (i.e. intensity of the vorticity, size of the vorticity and the structure of a hairpin-like vortex) were discussed as well as those on centre-of-gravity and surface motions of the bubble. In this study, a very small amount of surfactant (1-pentanol) solutions were examined. Although the bulk surface tension was almost the same as that of purified water, the bubble motion and the surrounding liquid motion in the solutions (i.e. contaminated system) were very different from those in purified water (i.e. purified system). A critical concentration of a surfactant was found out. At the critical concentration, the intensity and size of the vorticity become the largest. From the consideration of coupling the asymmetric surface motion of the bubble and the surrounding liquid motion, it was found out that the Marangoni stress owing to a concentration gradient of the adsorbed surfactant on the bubble surface plays a great role in both bubble and surrounding liquid motion.

The design rules for cross-wind vibrations given by DIN 4133 and the CICIND model code can give results that differ a factor 6 or more. Still, both design rules are included in the Eurocode. In this paper we apply a model closely related to the Vickery–Basu model, of which the CICIND model code and several other Codes of Practice are simplified derivates, to 13 industrial steel chimneys of which the operational history is known in some detail. The results are much more reliable than either DIN 4133 or the CICIND model code. The dominant parameter is the influence of turbulence on the aerodynamic damping parameter. This site specific parameter is neglected or too strongly simplified in all current Codes of Practice.

Obtaining solutions of the Eliassen balanced vortex model requires solving an invertibility relation, which is a nonlinear elliptic problem of the Monge-Ampere type. Multigrid techniques for this problem are investigated. An adaptive algorithm which combines the full multigrid method with continuation in a parameter related to the strength of the forcing is developed. Numerical results demonstrate the efficiency and robustness of this algorithm.

This paper furthers existing work into the instability mechanisms within the boundary-layer flow over a rotating sphere through the study of amplification rates within the convectively-unstable region. The onset of convective instability is associated with the experimentally observed onset of spiral vortices reported in the literature. Axial flow is found to stabilize the boundary layer by both delaying the onset of convective instability at all latitudes and also by significantly reducing the spatial amplification rates. We find that the type II (streamline curvature) mode becomes increasingly amplified with respect to the type I (crossflow) mode and is therefore likely to be selected in practice for sufficiently high axial flow rates. Furthermore, in experiments where special care is taken to remove all surface roughness, we predict that vortices will rotate at around 75% of the local surface speed. This is consistent with the experimental observations of Kobayashi & Arai who note a speed of around 76% under particular experimental conditions. These predictions are entirely consistent with related work on the rotating-disk and cone boundary layers.

In large-eddy simulations (LES) of gas-particle flows most investigators use single-phase subgrid scale (SGS) stress models. The Interaction between the two-phase SGS stresses is not fully taken into account. In this paper, a unified second-order moment (USM) two-phase SGS stress model for the LES of gas-particle flows is proposed, in which the interaction between the two-phase SGS stresses and anisotropy of the two-phase SGS stresses is fully taken into account. The proposed model is used in the LES of swirling gas-particle flows, together with RANS modeling using the USM two-phase turbulence model. The instantaneous results exhibit the multiple recirculating gas flow structure similar to that of the single-phase swirling flows, but the particle flow structure shows less vortices. The two-phase time-averaged velocities and RMS fluctuation velocities predicted by both LES-USM and RANS-USM models are almost the same and are in good agreement with the experimental results. However, for two-phase RMS fluctuation velocities, the LES-USM results are somewhat better than the RANS-USM results.

At finite weak mixing angle the sphaleron solution of Weinberg-Salam theory can be endowed with angular momentum proportional to the electric charge. Here we show, that this holds also for sphaleron-antisphaleron systems such as pairs, chains and vortex rings. We also address the equilibrium conditions for these solutions., 11 pages, 5 figures

Sharp-crested weirs are commonly used where highly accurate discharge measurements are needed to determine the flow rates in hydraulic laboratories, industrial applications and irrigation systems. Vortex theory and the definitive results obtained by Bazin and Scimeni were used to assess flow over rectangular sharp-crested weir and determine discharge coefficient. Laboratory facilities consisting of sharp-crested weirs with various widths and heights were used. The proposed theoretical analysis agreed well with the experimental observations. Also, the experimental data indicate that the suggested equation presents reasonable results for a large range of relative weir depths.

Breakup and spray formation of swirl liquid jets introduced into a low-speed cross-flow are experimentally investigated. Effects of the cross-flows on the macro and microscopic spray parameters are optically measured in terms of jet Weber number and liquid-to-gas momentum ratio. At lower jet Weber numbers, the liquid stream undergoes Rayleigh jet breakup. At higher momentum ratios, bag breakup occurs and tends to distort the liquid column into a loop-like structure. As the jet Weber number rises, stronger aerodynamic interaction and secondary flows cause multi-mode breakup. Regardless of the momentum ratio, the spray profile is hardly altered at higher jet Weber numbers. The cross-flow promotes the jet breakup and renders a finer spray in an entire range of injection velocities.

Extensive experimental research has been conducted using the particle image velocimetry (PIV), laser-induced fluorescence (LIF) imaging and backlit photographic recordings to study the complex interactions between coherent vortex structures created in the shear layer of jets and the bubbles. Triggering of the naturally-developing instabilities of the shear layer by a thin, pulsed annular flow surrounding the jets allowed the creation of large, orderly structures with controllable frequency and phase. Synchronization of the triggering with data acquisition permitted phase averaging of the data and revealed several interesting phenomena. In particular, the evolution of large vortices and bubble fields could be tracked and the interactions could be studied. The horizontal and vertical velocity components of the liquid and bubble fields and the vertical velocity of both the vortex and bubble rings that were created were measured by the PIV. LIF and image recordings have been combined to visualize bubble trapping inside large eddy structures.

We experimentally studied the dynamic-state characteristics of Josephson vortices (JVs) and influence of pancake vortices (PVs) on the JV dynamics in a stack of inductively coupled Bi2Sr2CaCuO8+δ intrinsic Josephson junctions. In a few-tesla magnetic field range, we observed Josephson-vortex-flow branches (JVFBs) in the current–voltage characteristics. We show that the JVFBs are generated by the non-collective pinning (depinning) of Josephson vortices in individual junctions by (from) pancake vortices. Results of our study suggest a convenient means of controlling JVs for quantum-electronics applications utilizing stacked Josephson junctions.

The ferroelectric domain structures in 1-3 type bulk magnetoelectric composites were studied using the phase-field method. The ferroelectric polarization distributions in triangle, square, circle, and other polygons-shaped rods embedded in a ferromagnetic matrix were obtained. The influences of ferroelectric particle size and symmetry and the surrounding magnetic phase medium on the stability of double vortex structures are discussed.

Three dimensional simulation of vortex dynamics based on main principles was studied by using Pancake model and Monte Carlo technique. The correlation strength between pancake vortices on adjacent layers was determined by comparing our simulation model with previous results. Point-like and columnar pinning were studied for a layered sample. At low temperatures where thermal effects ignored, columnar pinning centers were found to be more effective to demobilize vortices. At higher temperatures mobility of vortices were traced. Our results showed that melting occurred at around the same temperatures for both point-like and columnar pinning, although Columnar pinning has shown remarkable two-step melting.

In this work the structure of a spray resulting from the break-up of a conical liquid sheet was investigated through experimental techniques. The disperse and continuous phase velocities and the size of droplets were measured using a phase Doppler particle analyzer. A data post-processing, applying the generalized integral method, was used to evaluate liquid volume fluxes for different droplet size classes. The spatial distribution of the liquid flow was characterized by the radial mean spread and spatial dispersion parameters. It was found to be mainly influenced by the differences in droplet inertia and by the droplet collision phenomena. A high dispersion of droplet velocity module was measured at the spray densest region predicting high droplet collision rates. As a consequence of the coalescing collisions, a liquid flow rate transfer between size classes was detected as the spray developed. This process favoured the large size classes and caused the progressive increase of the droplet mean diameter.

In this paper, we study the single-vortex solutions of a two-dimensional high-$\kappa$ high-field Ginzburg–Landau model of superconductivity with a constant applied current. Under a nondegeneracy condition and for appropriate ranges of the applied magnetic field and applied current, we construct some special solutions which, up to a constant shift of phase in time, are the stationary solutions of the model equation. Our result provides partial justification for the existence of a critical applied current which is the one important step towards a rigorous mathematical characterization of the interactions between the quantized vortices and applied electric current.

The separated and reattaching turbulent flow over a surface-mounted two-dimensional square cylinder was experimentally studied by using time-resolved particle image velocimetry (TR-PIV). A total of 61,440 instantaneous image frames were acquired at a framing rate of 125 Hz, yielding a reliable result of the statistical quantities. The time-averaged features of the separated and reattaching flow were analyzed in terms of distributions of the velocity vectors, vorticity, the streamwise velocity fluctuation intensity and shear stress. The association between the large-scale vortical structures and spatial variation of these time-averaged quantities were thoroughly discussed. The unsteady features of the flow were revealed from distributions of the reverse-flow intermittency, space-time contour plot of the fluctuating streamwise velocity, and cross-correlation of the streamwise velocity. Subsequently, a comprehensive understanding of the contribution of the flow structures into the fluctuating flow field was gained by using a snapshot proper orthogonal decomposition (POD) analysis. The results showed that the linear combination of the first five POD modes, which capture 57% of the fluctuation energy, was capable of representing the large-scale behaviors of the separated and reattaching turbulent flow in the senses of spectrum, instantaneous feature and spatial variation of the velocity fluctuation intensity.

We study the dynamics of multi-vortex configurations to the Ginzburg–Landau dissipative/gradient flow equations with external potential in . We show that for initial data close to the widely spaced multi-vortex configurations, the effective dynamics of the vortex centres are governed by the inter-vortex forces and by external potential forces for weak and strong external potentials, respectively.

Numerous experimental results have suggested that the J c of YBa 2 Cu 3 O 7 (YBCO) films is significantly higher near the film–substrate interface than in the remainder of the film. We previously proposed that this effect is due to interfacial pinning enhancement caused by stress and the resulting misfit dislocations at the heteroepitaxial interface. To test this hypothesis we have used a non-superconducting PrBa 2 Cu 3 O 7− δ (PrBCO) buffer layer to minimize the lattice mismatch with YBCO. We find that the PrBCO layers lower J c of the 0.4 μm YBCO films in a predictable way, and that, if sufficiently thick (∼0.5 μm), they eliminate interfacial enhancement altogether. Our interpretation of this result is that the defects responsible for interfacial enhancement of flux pinning originate at the bottom of the non-superconducting PrBCO layer, which screens the pinning centers from vortices in YBCO. This result demonstrates that the pinning enhancement arises from stress at the film–substrate interface.