Spatial Structure Of Flow Research Articles

Complex system representation for vulnerability analysis

Many socio-technical systems are endowed of dynamism, self-organization, emergency etc. These attributes make them as complex systems. Because of this complexity, the representation is a crucial step for vulnerability analysis. The objective of this paper is to provide a generic framework of complex systems representation for vulnerability analysis. We used infrastructure network such as power grid, gas and telecommunication system to illustrate our proposal. It is separated in five layers: Spatial framework, Stake, Flow, Environment, and Network structure. The static view consists of a network structure (Nodes and edges). The dynamic view is related to the flow circulation, components’ states variations, and interdependences among them. Characteristics of these factors are described. The environment refers to outside perturbations that could happen. With our proposal it is possible to model many classes of complex system as the basis of vulnerability analysis. For this purpose, some modelling rules are proposed. The result allows performing simulations. Results of the simulation can be used for instance to find out vulnerability model into complex systems, or to validate existing models.

Diagnostics of swirl flow spatial structure in a vortex furnace model

The method of laser Doppler anemometry was applied for study of the spatial structure of a swirl turbulent flow occurred in isothermal lab-scale model of a vortex furnace (“CBTI design”). The criterion of “minimum of total pressure” was applied for visualization of a vortex core; the latter possesses a W-shaped geometry. Velocity and pressure pulsation spectra were measured for a wide range of operational parameters; these spectra testify about zero precession of a vortex core.

Stability of non‐parallel and parallel basic flows in the semi‐geostrophic model in isentropic coordinates

The energy‐Casimir method is employed to examine the stability of both non‐parallel and parallel basic flows in the semi‐geostrophic (SG) model in isentropic coordinates (ICs) based on the wave‐activity invariants. It is found that the stability criteria for non‐parallel basic flow under small‐amplitude disturbances are more complicated than those for parallel basic flow, and the spatial structure of basic flow at a horizontal boundary has a great impact on the stability of both parallel and non‐parallel basic flow. Results obtained in this work extend the stability results of Eliassen which are valid for parallel basic flow with non‐normal geostrophic flow as lateral boundary conditions. It is shown that, although there is a strong similarity between the SG model in ICs and the shallow‐water SG (SWSG) model, the finite‐amplitude stability theorems for the latter model cannot be extended to the SG model in ICs and the reasons for the failure are discussed.

Self-consistent mean flow description of the nonlinear saturation of the vortex shedding in the cylinder wake.

The Bénard-von Kármán vortex shedding instability in the wake of a cylinder is perhaps the best known example of a supercritical Hopf bifurcation in fluid dynamics. However, a simplified physical description that accurately accounts for the saturation amplitude of the instability is still missing. Here, we present a simple self-consistent model that provides a clear description of the saturation mechanism and quantitatively predicts the saturated amplitude and flow fields. The model is formally constructed by a set of coupled equations governing the mean flow together with its most unstable eigenmode with finite size. The saturation amplitude is determined by requiring the mean flow to be neutrally stable. Without requiring any input from numerical or experimental data, the resolution of the model provides a good prediction of the amplitude and frequency of the vortex shedding as well as the spatial structure of the mean flow and the Reynolds stress.

Dispersion modelling in complex terrain using wind climatologies

If annual mean values of concentration in complex terrain have to be determined, a representative wind climatology, which reflects local flow characteristics, is needed. This gives rise to two problems. First, observational data representative of the dispersion area are frequently not to hand. Second, the flow in the dispersion area itself may show a significant spatial structure, so transport is affected by varying wind speeds and directions. Both problems may be overcome by determining local wind climatologies by numerical modelling. The concept is to deduce terrain–dependent wind climatologies near the ground from the geostrophic wind climatology valid for the source region. Surface observations from the model area may also be included if available. If resulting surface wind climatologies are similar to each other within the dispersion area, then the variation of flow caused by the terrain structure need not be considered when modelling dispersion. In this case, Gaussian plume modelling may be used. If, however, the calculated wind climatologies differ significantly within the model area, then dispersion modelling has to take into account the spatial structure of the flow. This requires a Eulerian or a Lagrangian approach, because simpler methods of dispersion modelling are not capable of considering three–dimensional flow characteristics.

Stochastic Aspects of Mass Transport in Gas Diffusion Layers

The relationship between the 3D morphology of gas-diffusion layers (GDL) of HT-PEFCs and their functionality is analyzed. A stochastic model describing the microstructure of paper-type GDL is combined with the Lattice-Boltzmann method (LBM) to simulate gas transport within the GDL microstructure. Virtual 3D microstructures representing paper-type GDL are generated by a stochastic model, where the binder morphology is systematically modified. On these structures, single phase single component gas flow is computed by the LBM. Quality criteria evaluating the spatial homogeneity of gas supply are introduced and related to the binder morphology. The spatial homogeneity of the gas supply is analyzed by a parametrized stochastic model describing the gas flow at the exit of the GDL. This approach gives insight into the spatial structure of the gas flow at the GDL exit. The quality of gas supply is quantified by characterizing size and arrangement of regions with high gas supply. This stochastic gas flow model predicts the quality of gas supply for further binder morphologies. Analyzing the quality criteria and the stochastic evaluation of the spatial structure of the gas flow field at the GDL exit, it is found that the binder morphology has an essential influence on the gas supply.

Spatial and temporal resolution of a local Lorentz force flowmeter

Electromagnetic measurement techniques are very promising for accessing the flow properties of liquid melts. We extend one of the recently developed techniques, Lorentz force velocimetry, to the measurement of spatial flow structures close to the wall of the confining container. The sensor we use is called local Lorentz force flowmeter (L2F2). It comprises a small permanent magnet which is attached to a force measurement system. We demonstrate that it is possible to reconstruct the complex flow in the vicinity of the wall of a confined vessel using the L2F2. Additionally, we show with the help of a solid body experiment that the L2F2 responds to temporal changes in the flow in the order of 1 Hz.

Observations of the space-time structure of flow, turbulence, and stress over orbital-scale ripples

The spatial and temporal structure of flow, turbulence, and stress over equilibrium orbital-scale sand ripples are investigated at turbulence-resolving scales with a wide-band coherent Doppler profiler (MFDop) and an oscillating tray apparatus. The oscillation period and horizontal excursion were 10 s and 0.5 m. A single trial was also executed at 0.6 m excursion. Ripple wavelength and amplitude were 25 and 2.2 cm. Ensemble-averaged velocity profiles were acquired with 3 mm vertical resolution at 42 Hz. The spatial pattern of flow as a function of oscillation phase was determined by combining the phase-averaged velocity measurements from trials with the MFDop at different positions relative to a particular ripple crest. The MFDop measurements are used to investigate the coevolution of the lee vortex, turbulent kinetic energy, Reynolds stress, and turbulence production as a function of phase. Shear stress is determined from the vertically integrated vorticity equation and the double-averaged momentum equations. Friction factors obtained from the two methods are comparable and range from 0.1 to 0.2.

Flow Visualization on Lateral Multiple Jet Interaction with Freestream

The interaction flowfield of gaseous jets ejecting from three different orifice configurations into a Mach 5 turbulent crossflow over a flat plate was investigated experimentally. These jet configurations have equal equivalent throat diameter of 6 mm and nominal exit Mach number of 3. Schlieren photography was used to visualize the spatial flow structures; meanwhile surface oil flow patterns were employed to identify the separation and reattachment regions on the flat plate. Results show the influence of the jet-to-freestream static pressure ratio and jet configurations on flow interaction characteristics.

Editorial—the 4th International Workshop on Modeling the Ocean (IWMO 2012)

The 4th International Workshop on Modeling the Ocean (IWMO; http://www.jamstec.go.jp/frcgc/jcope/htdocs/e/ iwmo2012.html) was held on May 21–24, 2012 in the vibrant city of Yokohama on the Tokyo Bay, Japan. TheWorkshop was hosted by Japan Agency for Marine-Earth Science and Technology (JAMSTEC)—the home of the famous “Earth Simulator”—one of the world's most powerful supercomputers dedicated for simulating the complex interactive processes of the earth and its environment. Over 100 researchers worldwide participated in the Workshop, which included two keynote lecturers, by Professor Mellor of Princeton University and Professor Yamagata of the University of Tokyo, and more than 80 oral presentations and 20 posters. The topics covered in the Workshop, as in the past IWMO's, are wide-ranging, from small-scale waves and estuarine processes to large-scale eddy and multi-decadal climate dynamics. In part thanks to the generosity of the host, a new record of 30 graduate students and postdocs participated in the Outstanding Young Scientist Award Competition, some with truly outstanding presentations of top scientific rigors. The collection of 11 papers in this Topical Collection was selected from a total of 22 originally submitted after they underwent the usual process of reviews and revisions. There were at least two reviewers for each paper, but a few submissions had more. The reviews were solicited from both the Workshop attendees and the scientific community at large. The subjects of papers in this Topical Collection include two on regional processes (Ezer and Oey 2013; Miyama and Miyazawa 2013), three on surface and upper-layer physics (Goh and Noh 2013; Mellor 2013; Ponte and Klein 2013), one on global modeling (Exarchou et al. 2012), three on coastal processes (Gao et al. 2013; Lu et al. 2013; Wang et al. 2013a), and two on analyses of model outputs (Wang et al. 2013b; Wu and Wang 2013). Ezer and Oey (2013) use the results of high-resolution numerical experiments based on the Princeton Ocean Model (POM) of the Bering Sea (Ezer and Oey 2010) to study the dynamics of strait flows. Three distinct categories of strait dynamics are identified: shallow passages with near barotropic flows, wide passages which are driven bymesoscale eddies, and deep passages which have persistent baroclinic currents with deep return flows. Universal relations are found between the radius of deformation of each strait and the observed variability. Empirical Orthogonal Function (EOF) analyses reveal the spatial structure and forcing of the strait flows. The model shows that mesoscale variability in the Bering Sea originate from two Responsible Editor: Jorg-Olaf Wolff

A Numerical Study of Salt Fluxes in Delaware Bay Estuary

AbstractThe results of a numerical study of Delaware Bay using the Regional Ocean Modeling System (ROMS) are presented. The simulations are run over a range of steady river inputs and used M2 and S2 tidal components to capture the spring–neap variability. Results provide a description of the spatial and temporal structure of the estuarine exchange flow and the salinity field, as well the along-channel salt flux in the estuary. The along-channel salt flux is decomposed into an advective term associated with the river flow, a steady shear dispersion Fe associated with the estuarine exchange flow, and a tidal oscillatory salt flux Ft. Time series of Fe and Ft show that both are larger during neap tide than during spring. This time variability of Ft, which is contrary to existing scalings, is caused by the lateral flows that bring velocity and salinity out of quadrature and the stronger stratification during neap tide, which causes Ft to be enhanced relative to spring tide. A fit for the salt intrusion length L with river discharge Q for a number of isohalines is performed. The functional dependences of L with Q are significantly weaker than Q−1/3 scaling. It is concluded that the response of the salt field with river discharge is due to the dependence of Fe and Ft with Q and the relative importance of Ft to the total upstream salt flux: as river discharge increases, Fe becomes the dominant mechanism. Once Fe dominates, the salt field stiffens because of a reduction of the vertical eddy viscosity with increasing Q.

Down-slope cascading modulated by day/night variations of solar heating

Sloping sides of natural basins favour the formation of cross-shore temperature gradients (differential coastal heating/cooling), which cause significant littoral-pelagial water exchange. Autumnal denser water cascading along a sloping lake boundary, modulated by day/night variations of solar heating is considered numerically, in order to reveal the development of the cascading process in time, spatial structure of the exchange flows, and diurnal variations of volumetric flow-rate of littoral-pelagial exchange flow, as well as to compare its daily maxima at different depths/cross-sections, with known quasi-steady state predictions under constant buoyancy flux. The development of exchange flows progress through two phases: i) appearance and adjustment to day/night buoyancy flux variations; and ii) quasi-steady exchange, when variations of the flow rate in every next diurnal cycle are more or less the same as the previous day. The duration of the first phase depends on local depth (~1 day for depths of about 10 m, ~2 days for depths 15-25 m, and ~5 days down to 30 m for the considered initial linear vertical temperature stratification). Maximum horizontal exchange takes place in the cross-section where the thermocline meets the slope, and the cold down-slope currents detach from the bottom. The location of this cross-section advances off-shore with time, in accordance with the deepening of the upper mixed layer. The existence of a specific coastal circulation cell, with different water dynamics from those above the main part of the slope, is a characteristic feature of horizontal convective exchange. The mean value of the specific volumetric flow rate of the convective exchange, driven by day/night oscillations in its fully developed quasi-steady phase increases almost linearly with local depth, and is about twice as large as the quasi-steady exchange values, predicted by formula Q=0.0013·d1.37 (Q is measured in m2 s-1, and local depth above the slope d in m), suggesting that the thermal siphon, energized by oscillating day/night buoyancy fluxes, flushes coastal regions twice as efficiently as the cascading, developing under (more or less) uniform external conditions in field observations and laboratory experiments, which lie behind the given formula. Flushing time in the considered case has an order of 10-60 hours for a littoral zone of 6-30 m depth. Application of convective phase diagrams (e.g., Q vs ΔT) is suggested as a convenient way to describe the day/night convective exchange, allowing for visualization of the flow development process, its coherency and the time lag of the development at different depths.

Experimental and Computational Methods for Flow Investigation in High-Speed Multistage Compressor

This study takes place in the frame of a research project to better understand the flow that develops in multistage high-speed compressors. First, the paper presents the high-speed 3.5-stage compressor CREATE and the methods that are considered to increase the data reliability and the investigation capability with such realistic compressors. Second, flow simulations, achieved with three-dimensional unsteady Reynolds-averaged Navier-Stokes computations over the whole compressor spatial and temporal periodicities, are analyzed through a study of their sensitivity to some parameters such as the inlet conditions, the space and time discretization, and technological effects such as tip and hub clearances. Finally the paper focuses on the methodology used to compare the experimental and numerical results over the whole compressor periodicities. The local spatial and temporal flow structures are well estimated. The key is the advection of these structures, which interact with each other and produce a significant part of the flow fluctuations in the downstream stages. The paper presents the zone close to the casing, where losses and blockage are induced by the interaction between the tip leakage flow and the incoming wakes. This is where the numerical simulation has to be improved, in order to accurately predict the performance.

Determining the structure of the flow in a flow of high pressure turbine

The results of the current study the spatial turbulent fluid flow in a flow of high-pressure turbines. The results of calculation of the spatial structure of flow and energy losses in the supply of the radial-axial turbines

Airborne Doppler Lidar Measurements of Valley Flows in Complex Coastal Terrain

AbstractThree-dimensional winds obtained with an airborne Doppler lidar are used to investigate the spatial structure of topographically driven flows in complex coastal terrain in Southern California. The airborne Doppler lidar collected four hours of data between the surface and 3000 m MSL along a 40-km segment of the Salinas Valley during the afternoon of 12 November 2007. The airborne lidar measurements, obtained at horizontal and vertical resolutions of approximately 1500 and 50 m, respectively, reveal a detailed spatial structure of the atmospheric flows within the valley and their associated aerosol features. Clear skies prevailed on the flight day with northwesterly synoptic flows around 10 m s−1. The data document a shallow sea breeze making a transition into an upvalley flow in the Salinas Valley that accelerates in the upvalley direction. Along with the acceleration of the upvalley wind, the lidar data indicate the presence of enhanced sinking motions. No return flows associated with the sea-breeze or upvalley flows are observed. While synoptic flows are aligned along the valley axis in the upvalley direction, lidar data indicate the presence of a northerly cross-valley flow around the height of the surrounding ridges. This flow intrudes into the valley atmosphere and induces, along with thermally driven slope flows on the sunlit valley sidewall, a cross-valley circulation that causes an asymmetric distribution of the aerosols. This study demonstrates the large potential of airborne Doppler lidar data in describing flows in complex terrain.

Application of modern optical methods for detecting the spatial structure of turbulent flames

A number of modern optical methods used for diagnostics of reactive flows are described. Various aspects of using advanced modifications of particle image velocimetry (Stereo-PIV, High-repetition PIV, and Tomo-PIV) for measuring instantaneous velocity fields in reactive flows are discussed in detail. Capabilities of PIV and spectroscopy of flame radiation (CH* radical) in obtaining data on the spatial flow structure and the flame are demonstrated by an example of studying a swirled turbulent propane-air flame and an isothermal jet.

Diagnostic complex for the modelling and experimental investigation of the spectral and gas-dynamic characteristics of an inductively coupled plasma

A diagnostic complex has been developed for the modelling and experimental investigation of the gas-dynamic and spectral characteristics of an inductively coupled plasma. This complex includes a four-dimensional computer model of plasma, a research plasma generator, a schlieren system for visualizing the spatial structure of gas flows in the torch, and a high-resolution spectrometer for obtaining information on the temperature in the discharge zone from the intensity of the emission spectra. The model adequately maps the gas-flow dynamics in the torch with no discharge ignited in the inductively coupled plasma. The results of the calculations agree well with the experimental data.

Turbulent flow separation and characteristics of heat transfer under unsteady hydrodynamic conditions

Results from an experimental study of hydrodynamics and heat transfer in turbulent separation flow under the conditions of its periodic pulsations are presented. It is found that an essential change occurs in the spatial and timing structure of separation flow under the effect of superimposed unsteadiness. Phenomena involving reduction of the longitudinal dimensions of the separation region and essential enhancement of heat transfer in the separation region of pulsating flow are revealed. The physical mechanism of these phenomena is described.

Experimental Investigation on Zonal Structure in Drag-Reducing Channel Flow with Surfactant Additives

The spatial structure of a drag-reducing channel flow with surfactant additives in a two-dimensional channel was investigated experimentally. We carried out detailed measurements of the instantaneous velocity in the streamwise wall-normal plane and streamwise spanwise plane by using particle image velocimetry (PIV). The surfactant used in this experiment is a kind of cationic surfactant CTAC. The weight concentrations of the CTAC solution were 25 and 40 ppm on the flow. We considered the effects of Reynolds number ranging from 10000 to 25000 and the weight concentration of CTAC. The results of this paper showed that in the drag-reducing flow, there appeared an area where the root mean square of streamwise velocity fluctuation and the vorticity fluctuation sharply decreased. This indicated that two layers with different turbulent structure coexisted on the boundary of this area. Moreover, these layers had characteristic flow structures, as confirmed by observation of the instantaneous vorticity fluctuation map.

Diagnosing indirect-drive inertial-confinement-fusion implosions with charged particles

High-energy charged particles are being used to diagnose x-ray-driven implosions in inertial-confinement fusion. Recent measurements with vacuum hohlraums have resulted in quantitative characterization of important aspects of x-ray drive and capsule implosions. Comprehensive data obtained from spectrally resolved, fusion-product self-emission and time-gated proton radiographs with unprecedented clarity reveal new and important phenomena. Several types of spontaneous electric fields differing by two orders of magnitude in strength are observed, the largest being on the order of one-tenth of the Bohr field (, where a0 is the Bohr radius). The hohlraum experiments demonstrate the absence of stochastic filamentary patterns and striations around the imploded capsule, a feature common to direct-drive implosions. The views of spatial structure and temporal evolution of spontaneous electromagnetic fields, plasma flows, implosion symmetry and dynamics provide insight into the physics of x-ray driven implosions. Potential applications for the National Ignition Facility are outlined.