Internal Velocity Distribution Research Articles

EFFECT OF BUILDING PLAN FORM ON HUMAN THERMAL COMFORT IN NATURALLY VENTILATED OPEN-PLAN ENCLOSURES LOCATED IN HOT CLIMATES

This study aims to examine the effect of building plan form on internal thermal comfort conditions in naturally ventilated open-plan buildings located in hot climates. The study examined the square and the rectangular plan forms in relation to several values of wind direction, building plan depth, and climatic conditions. The study utilised CFD for ventilation prediction, DesignBuilder for thermal modelling, and the Tropical Summer Index (TSI) for thermal comfort assessment. These three tools were integrated in a quantitative approach to fulfil the study aim. The study concluded that the use of area-weighted average velocity magnitude is more accurate in the assessment of natural ventilation performance, as it accounts for both internal velocity magnitude and distribution. The study confirmed the common observation that the use of shallow building plans is more effective to increase internal air velocity and improve internal thermal comfort. At some point of increased plan depth, the internal air velocity magnitude dramatically decreases. In the three examined wind directions, this occurred when the plan depth exceeded 3H in the square cases and 2.5H in the rectangular ones, where H is the building height. This value is much less than the commonly recommended maximum value of 5H. The study also concluded that reducing building depth in the square cases has generally more potential to improve thermal comfort conditions when compared with the rectangular cases. The gross increase in Percentage of People Comfortable, PPC, in all the examined cases was 23% in the square cases, compared to 11% in the rectangular cases.

Experimental Research of Air Supply Characteristics of Ejection-permeation Fabric Air Dispersion System in a Large Space Building

In this paper, the air supply characteristics of an ejection-permeation fabric air dispersion system (EFADS) including internal pressure distribution, internal air velocity distribution and orifices air velocity distribution along the system in a large space building were experimentally studied by changing air temperature and air supply flow rate. Meanwhile, indoor air velocity field was experimentally tested. The results indicate that along the EFADS’s flow direction the internal total pressure and internal dynamic pressure decreases slightly, and the internal static pressure increases. The internal air velocity is proportional to air supply volume along the flow direction. The internal air velocity distribution is similar in each condition when the distance from the inlet is more than 4.5m. The air velocity in the indoor occupied area is relatively stable under various representative conditions. And the velocity of most of the indoor measured points is less than 0.4m/s when air supply volume is larger.

Fluid convection and solidification mechanisms of liquid Fe50Cu50 alloy under electromagnetic levitation condition

In the electromagnetic levitation experiment, the liquid flow in the undercooled liquid alloy remarkably affects the relevant thermodynamic property measurement and solidification microstructure. Therefore, it is of great importance to understand the fluid convection inside the undercooled melt. Theoretical calculation and electromagnetic levitation experiment have been used to investigate the internal velocity distribution and rapid solidification mechanism of Fe50Cu50 alloy. Based on axisymmetric electromagnetic levitation model, the distribution patterns of magnetic flux density and inducted current for levitated Fe50Cu50 alloy are calculated together with the mean Lorenz force. The Navier-Stokes equations are further taken into account in order to clarify the internal fluid flow. The results of the theoretical calculation reveal that the fluid velocity within levitated melt is strongly dependent on three factors, i.e., current density, current frequency and melt undercooling. As one of these factors increases, the maximum fluid velocity decreases while the average fluid velocity increases. Meanwhile, the area with fluid velocity larger than 100 mm·-1 is significantly extended. Furthermore, the fluid flow within levitated melt displays an annular tubular distribution characteristic. The Fe50Cu50 alloy melt is undercooled and solidified under electromagnetic levitation condition. In this undercooling regime △ T50Cu50 alloy melt has suppressed phase separation substantially. Once the undercooling attains a value of 150 K, metastable phase separation leads to the formation of layered pattern structure consisting of floating Fe-rich zone and sinking Cu-rich zone. A core-shell macrosegregation morphology with the Cu-rich zone distributed in the center and outside of the sample and Fe-rich zone in the middle occurs if the undercooling increases to 204 K. With the enhancement of undercooling after phase separation, the grain size of α -Fe dendrites in Cu-rich zone presents a decreasing trend. In contrast to the phase separated morphology of Fe50Cu50 alloy under the glass fluxing condition, the phase separated morphologies show obviously different characteristics. In such a case, the forced convection induced by electromagnetic stirring results in the formation of wavy interface between Fe-rich and Cu-rich zones, the distorted morphology of the Cu-rich spheres distributed in the Fe-rich zone, and the increased appearance probabilities of Cu-rich spheres at the upper part of electromagnetically levitated sample. Experimental observations demonstrate that the distribution pattern of Cu-rich spheres in Fe-rich zone is influenced by the tubular fluid flow inside the melt.

Anisotropic collisions of dipolar Bose–Einstein condensates in the universal regime

We report the measurement of collisions between two Bose–Einstein condensates with strong dipolar interactions. The collision velocity is significantly larger than the internal velocity distribution widths of the individual condensates, and thus, with the condensates being sufficiently dilute, a halo corresponding to the two-body differential scattering cross section is observed. The results demonstrate a novel regime of quantum scattering, relevant to dipolar interactions, in which a large number of angular momentum states become coupled during the collision. We perform Monte-Carlo simulations to provide a detailed comparison between theoretical two-body cross sections and the experimental observations.

Radio reflection imaging of asteroid and comet interiors II: Results and recommendations

We modeled orbital surface-penetrating radar of an asteroid and comet using two-dimensional finite-difference wavefield migration, in order to assess key target properties and experiment parameters required to fully image internal structure. Migration places radar echoes in their correct positions in a complex subsurface and is a complementary tool to travel-time tomography. The target shape was scaled from 433 Eros to 0.5-km mean diameter for an asteroid and 10km for a comet. The interiors were populated with a power-law distribution of spherical blocks. We used an image structural similarity index to compare the internal surfaces reconstructed under different assumptions to a “best” image using optimum parameters. We found that successful internal imaging of the asteroid was not sensitive to whether the block interstices were regolith or void. Frequency dependence between 5 and 15MHz was also minor. Internal interfaces could also be imaged if the attenuation was higher than that inferred within volcanic plains on Mars, but not as high as measured in a strongly fractured volcanic tuff on Earth. The overall imaging quality for the comet was statistically similar to the asteroid, but there was less variability due to smaller internal contrasts. A key finding is that imaging was vastly improved by using a second spacecraft as a radar receiver. A subsatellite with a different orbit will eventually provide a range of different illumination geometries over each part of the target. Finally, the results depend strongly on the specified internal velocity distribution, representing partial progress in complementary tomographic velocity estimation. The modeled impedance contrasts within the asteroid are larger than those typically encountered in exploration seismology and very much larger than in medical imaging, and so the velocity used to migrate the reflections must be close to the actual distribution. This again emphasizes the need for joint traveltime tomography and wavefield migration for asteroid imaging, which is optimized using two orbiters.

The flow structure of jets from transient sources and implications for modeling short‐duration explosive volcanic eruptions

AbstractWe used laboratory experiments to examine the rise process in neutrally buoyant jets that resulted from an unsteady supply of momentum, a condition that defines plumes from discrete Vulcanian and Strombolian‐style eruptions. We simultaneously measured the analog‐jet discharge rate (the supply rate of momentum) and the analog‐jet internal velocity distribution (a consequence of momentum transport and dilution). Then, we examined the changes in the analog‐jet velocity distribution over time to assess the impact of the supply‐rate variations on the momentum‐driven rise dynamics. We found that the analog‐jet velocity distribution changes significantly and quickly as the supply rate varied, such that the whole‐field distribution at any instant differed considerably from the time average. We also found that entrainment varied in space and over time with instantaneous entrainment coefficient values ranging from 0 to 0.93 in an individual unsteady jet. Consequently, we conclude that supply‐rate variations exert first‐order control over jet dynamics, and therefore cannot be neglected in models without compromising their capability to predict large‐scale eruption behavior. These findings emphasize the fundamental differences between unsteady and steady jet dynamics, and show clearly that: (i) variations in source momentum flux directly control the dynamics of the resulting flow; (ii) impulsive flows driven by sources of varying flux cannot reasonably be approximated by quasi‐steady flow models. New modeling approaches capable of describing the time‐dependent properties of transient volcanic eruption plumes are needed before their trajectory, dilution, and stability can be reliably computed for hazards management.

Analysis and Evaluation of Wind Turbine Flow Field and Noise Simulation Based on CFD Software

CFD is the abbreviation of the computational fluid dynamics, which is widely used in engineering fluid simulation. Based on two-dimensional N-S equation and k-e turbulence model, this paper uses FLUENT software, finite volume method and SIMPLEC algorithm to do numerical simulation and analysis on flow field in centrifugal fan. In order to improve the efficiency and accuracy of calculation, this paper uses AutoCAD to establish the two-dimensional model of fan, and uses the structured triangular mesh to divide grid. Encrypting the blade can improve the precision and also save the computer memory. Through the calculation we get the internal flow field velocity and pressure distribution in the wind turbine, and get the power level cloud of internal noise in fan. It provides the technical reference for the optimization design of wind turbine.

Surface slopes, velocity profiles and fluid pressure in coarse-grained debris flows saturated with water and mud

AbstractData on the internal velocity distribution of flowing sediment–fluid mixtures such as debris flows are rare, but necessary for model development and testing. A probe to measure the mean particle velocity at different depths and different locations within experimental debris flows in a 4 m diameter rotating drum was developed. In addition, the flow depth, basal normal stress and basal pore fluid pressure were also measured. Results show that for a given sediment–fluid mixture the velocity profiles collapse to distinct non-dimensional profiles. Macroscopic flow behaviour shows great similarity, with mean surface slopes weakly dependent on the shear rate for water-saturated gravel, but strongly shear-rate-dependent when pores are filled with mud. Poorly sorted material with a high content of fines produced fluid pressures close to normal stress and sidewall friction had a strong effect on the flow pattern. Our results reveal variability in profile characteristics for flows displaying similar macro-dynamics and provide data for model testing.

Numerical Simulation and Orthogonal Design Method Research Effect of Splitter Blade's Main Geometry Factors on the Performance of Pump as Turbine

In order to research the effect of splitter blades main geometry factors on the performance of pump as turbine, the L9(34)orthogonal design scheme has been developed based on four factors which contain the blades circumferential biasing degrees, the outlet deflection angle, the outlet diameter and the number of blade. According to this design scheme, numerical simulation of centrifugal pump (ns48) as turbine has been done. By range analysis of computational results, the best design scheme of splitter blades and the level of each factor for the primary and secondary order of turbine efficiency (the outlet deflection angle, the outlet diameter, the number of blade, and blades circumferentially biasing degrees) are obtained. The internal characteristics analysis was done on centrifugal pump (ns48) as turbine at its optimal operating conditions. The results shows, compared with conventional impeller, that the internal velocity and pressure field distribution using the design scheme of composite impeller is more reasonable.

225 空間フィルタ流速計を用いた液滴速度の測定(OS-2 流体計測技術の向上とその応用(3),オーガナイズド・セッション(OS))

225 空間フィルタ流速計を用いた液滴速度の測定(OS-2 流体計測技術の向上とその応用(3),オーガナイズド・セッション(OS))

Universality of the holographic angular momentum cutoff

The AdS/CFT dual description of a peripheral heavy ion collision involves an asymptotically AdS rotating black hole. The explicitly known black holes of this kind, with planar event horizon topology [the “KMV0” spacetimes], have been shown to be unstable when string-theoretic effects are taken into account. It has been argued that this implies a “holographic” angular momentum cutoff for peripheral collisions at very high energies. However, the KMV0 black hole corresponds to a specific velocity distribution in the aftermath of a peripheral collision, and this distribution is not realistic at all points of the interaction zone. It could therefore be argued that the angular momentum cutoff is an artefact of this particular choice of bulk geometry. We demonstrate that, on the contrary, a quark–gluon plasma with any physically reasonable internal velocity distribution corresponds to a black hole which is still unstable, in the same way as the KMV0 spacetime. The angular momentum cutoff is therefore a universal prediction of the holographic description of these collisions.

Study of dynamic hydrophobicity of micro-structured hydrophobic surfaces and lotus leaves

The dynamic wetting characteristics of water droplets on silicon wafers with microscale regular pillars structures and fresh lotus leaves are investigated experimentally. We measured the static contact angle, contact angle hysteresis, and roll-off angle of water droplets on both of these superhydrophobic surfaces with a high speed contact angle meter. The dynamic contact angles and internal velocity distribution of water droplets on superhydrophobic surfaces were studied with a high-speed camera system and a particle image velocimetry (PIV) system, respectively. We found that the acceleration of water droplets when they slide off lotus leaves is greater than that of water droplets sliding off the silicon wafers with microscale pillar structures although the static contact angles of water droplets on lotus leaves are slightly smaller than those on the silicon wafers. The reason is that water droplets sliding off lotus leaves have smaller contact angle hysteresis and larger slip velocities. These results indicate that the dynamic contact angle hysteresis and sliding acceleration of liquid droplets are more suitable for reflecting the hydrophobicity of material surfaces compared with static contact angles. Our experiments also show that lotus leaves with multiscale micro/nanostructures have stronger hydrophobicity and self-cleaning properties compared with the micro-structured superhydrophobic surfaces.

Evidence of a link between the evolution of clusters and their AGN fraction

We discuss the optical properties, X-ray detections and active galactic nucleus (AGN) populations of four clusters at z ~ 1 in the Subaru–XMM Deep Field (SXDF). The velocity distribution and plausible extended X-ray detections are examined, as well as the number of X-ray point sources and radio sources associated with the clusters. We find that the two clusters that appear virialized and have an extended X-ray detection contain few, if any, AGN, whereas the two pre-virialized clusters have a large AGN population. This constitutes evidence that the AGN fraction in clusters is linked to the clusters' evolutionary stage. The number of X-ray AGN in the pre-virialized clusters is consistent with an overdensity of a factor of ~200; the radio AGN appear to be clustered with a factor of 3 to 6 higher. The median K-band luminosities of L_K= 1.7 ± 0.7 L* for the X-ray sources and L_K= 2.3 ± 0.1 L* for the radio sources support the theory that these AGN are triggered by galaxy interaction and merging events in sub-groups with low internal velocity distributions, which make up the cluster environment in a pre-virialization evolutionary stage.

Internal state populations and velocity distributions of monatomic species ejected after the 1064 nm laser irradiation of barium

The plumes accompanying 1064 nm nanosecond pulsed laser ablation of barium in vacuum at three moderate incident laser fluences in the range of 5.3–10.8 J/cm2 have been studied using both wavelength and time resolved optical emission spectroscopy and time-of-flight laser-induced fluorescence. Neutral atoms and both singly and doubly charged monatomic cations in excited states up to near the corresponding ionization limits are identified in the optical emission spectra. The population distributions of low-lying (≤1.41 eV) “dark” states of Ba atoms measured by laser-induced fluorescence revel that the metastable D3J and D12 abundances in the plume are higher than predictions based on assuming a Boltzmann distribution. The D3J and D12 populations are seen, respectively, to decrease slightly and nearly no vary with raising fluence, which contrasts with the increasing trend that is observed in the ground-state Ba(S10) population. At all fluences, the time-of-flight distributions of the whole dark states and of various of the emitting levels are bimodal and well described by Maxwell–Boltzmann and shifted Maxwell–Boltzmann velocity functions, respectively, with different average translational temperatures ⟨T⟩ for each state. The ⟨T⟩ values for the dark states are insensitive to the fluence, while for all emitting species marked variations of ⟨T⟩ with fluence are found. These observations have been rationalized in terms of material ejection from the target being dominated by a phase explosion mechanism, which is the main contributor to the Ba(S10) population. Thermionic emission from the target surface can also release initial densities of free electrons and cations which, at the prevailing irradiances, will arguably interact with the incident laser radiation by inverse bremsstrahlung, leading to further excitation and ionization of the various plume species. Such a heating mechanism ensures that the energy injected to the plume will alter the propagation velocities of the primary inverse bremsstrahlung absorbers, i.e., cations, to a major extent than those of neutral atoms with increasing fluence. Electron-ion recombination occurring early in the plume expansion can lead to the generation of both neutral and ionic species in a manifold of long-lived Rydberg states, from which a radiative cascade will likely ensue. The distinct fluence dependences of the Ba(D3J) and Ba(D12) populations and velocity distributions show up the major complexity that distinguishes their populating mechanisms with respect to the remaining species.

E205 液中ジェット界面における内部流動と周囲流動との相互作用(高速炉基盤技術,OS8 軽水炉・新型炉・核燃料サイクル)

For the safety design of the Fast Breeder Reactor (FBR), it is strongly required that the Post Accident Heat Removal (PAHR) is achieved after a hypothetical Core Disruptive Accident (CDA). In the PAHR, it is important that the molten core material is fragmented to be solidified by the sodium coolant and it is necessary to evaluate the jet breakup length. Although there are many previous studies on the jet breakup length, the tendency of jet breakup length is different for the previous studies. To estimate jet breakup length, it is necessary to clarify the influence of fragmentation behavior on jet surface and on jet breakup behavior in coolant, In present study, experiments are conducted to obtain interfacial fragmentation behavior by injecting transparent fluid in water. Internal and external velocity distributions of the jet are measured by PPV technique. Reynolds stress, turbulent energy and shear stress are evaluated from the velocity data. As the results, Reynolds stress and turbulent energy become large in the vicinity of jet surface. Vortex around interfacial wave is observed. Local shear stress acts on the interfacial wave. Mechanism of fragmentation and interaction of jet internal flow and surrounding flow through interface are discussed.

Dynamical Effects of Cold Dark Matter Subhalos on a Galactic Disk

Abstract We have investigated the dynamical interaction between a galactic disk and numerous surrounding dark subhalos as expected for a galaxy-sized halo in the cold dark matter models. Our particular interest is to what extent accretion events of subhalos into a disk are allowed in light of the observed thinness of a disk. Several models of subhalos were considered in terms of their internal density distribution, mass function, and spatial and velocity distributions. Based on a series of $N$-body simulations, we find that disk thickening, quantified by the change of its scale height, $\Delta z_{\mathrm{d}}$, depends strongly on the individual mass of an interacting subhalo, $M_\mathrm{sub}$. This is described by the relation $\Delta z_{\mathrm{d}} / R_{\mathrm{d}} \simeq 8 \sum_{j=1}^N (M_{\mathrm{sub},j} / M_{\mathrm{d}})^2$, where $R_{\mathrm{d}}$ is the disk scale length, $M_{\mathrm{d}}$ is the disk mass, and $N$ is the total number of accretion events of subhalos inside a disk region ($\le 3 R_{\mathrm{d}}$). Using this relation, we find that an observed thin disk has never interacted with subhalos with a total mass of more than 15% of the disk mass. Also, a less-massive disk with a smaller circular velocity, $V_{\mathrm{c}}$ is more affected by subhalos than a disk with a larger $V_{\mathrm{c}}$, in agreement with observations. Further implications of our results for the origin of a thick disk component are also discussed.

The Velocity and Mass Distribution of Clusters of Galaxies from the CNOC1 Cluster Redshift Survey

In the context of the CNOC1 survey, redshifts were obtained for galaxies in 16 clusters. The resulting sample is ideally suited for an analysis of the internal velocity and mass distribution of clusters. Previous analyses of this data set used the Jeans equation to model the projected velocity dispersion profile. However, the results of such an analysis always yield a strong degeneracy between the mass density profile and the velocity dispersion anisotropy profile. Here we analyze the full (R,v) data set of galaxy positions and velocities in an attempt to break this degeneracy. We build an cluster from the individual clusters under the assumption that they form a homologous sequence; if clusters are not homologous then our results are probably still valid in an average sense. To interpret the data we study a one-parameter family of spherical models with different constant velocity dispersion anisotropy, chosen to all provide the same acceptable fit to the projected velocity dispersion profile. The best-fit model is sought using a variety of statistics, including the likelihood of the data set and the shape and Gauss-Hermite moments of the grand-total velocity histogram. The confidence regions and goodness of fit for the best-fit model are determined using Monte Carlo simulations. Although the results of our analysis depend slightly on which statistic is used to judge the models, all statistics agree that the best-fit model is close to isotropic. For none of the statistics does the 1 σ confidence region extend below σr/σt = 0.74, or above σr/σt = 1.05. This result derives primarily from the fact that the observed grand-total velocity histogram is close to Gaussian, which is not expected to be the case for a strongly anisotropic model. The best-fitting models have a mass–to–number density ratio that is approximately independent of radius over the range constrained by the data. They also have a mass density profile that is consistent with the dark matter halo profile advocated by Navarro, Frenk, & White in terms of both the profile shape and the characteristic scale length. This adds important new weight to the evidence that clusters do indeed follow this proposed universal mass density profile. We present a detailed discussion of a number of possible uncertainties in our analysis, including our treatment of interlopers and brightest galaxies, our use of a restricted one-parameter family of distribution functions, our use of spherical models for what is in reality an ensemble of nonspherical clusters, and our assumption that clusters form a homologous set. These issues all constitute important approximations in our analysis. However, none of the tests that we have done indicates that these approximations influence our results at a significant level.

THE INTERNAL FLOW AND EXIT CONDITIONS OF PRESSURE SWIRL ATOMIZERS

A computational fluid dynamics model and experiments are used to obtain information on the internal flow of pressure swirl atomizers and their outlet conditions. At the Reynolds numbers typical of many applications, fully turbulent flow is not expected internally so that a time-stepping laminar-flow solution procedure is used. The computed air-core topology, atomizer discharge coefficient, and spray angle agree well with measurements for several internal geometry shapes. The computed velocity distributions generally agree with published laser Doppler anemometer measurements. In a manner dependent on Reynolds number and internal geometry, the velocity fields differ significantly from those assumed in approximate inviscid analyses of swirl atomizers. The most obvious differences are preferences for the flow through the atomizer to concentrate either near the air core or near the wall, and also the occurrence of secondary motion, particularly Görtler vortices near the swirl chamber wall. The modeling technique is particularly useful for predicting the velocity profiles in the liquid sheet at the atomizer exit. Although atomizer discharge coefficient may not vary greatly for variation of the atomizer convergence geometry, these velocity profiles do vary. Viscous losses in the atomizer, for a given Reynolds number, are related to changes in the internal velocity distribution. Air-core surface waves are noted in the experiments and these waves influence the sheet and its breakup downstream. The secondary motion predicted in the liquid inside the atomizer may be a source of perturbation for these waves.

Grid and Particle Hydrodynamics:: Beyond Hydrodynamics via Fluid Element Particle-in-Cell

A new plasma/fluid transport algorithm is presented that combines and retains the strengths of the particle and hydrodynamic methods. By including internal velocity characteristics of real particles within each finite size macro-particle (FSP), a redundancy is introduced in the representation of the real particle distribution that is recovered by the superposition of these macro-particles. This redundancy is exploited by merging particles that sufficiently overlap in parameter space. The internal velocity distribution is exploited by allowing the distribution within each FSP to evolve hydrodynamically. In turn the evolution establishes the partitioning of moments into central and expansion particles. Such aggressive increases in the number of individual FSPs probe for emerging features. If interesting features fail to materialize, aggressive merging provides particle economy. The objective is to economically recover details of the particle distribution necessary for accurate collisions. GaPH promises to accomplish this mission without squandering computational resources in uninteresting regions of phase space. This paper reports collisionless GaPH test results that compare well with analytic solutions that initially contain large gradients.

Measurements of the velocity distribution in ping-pong-ball avalanches

Dense-flow avalanches may be simulated as granular flows. In this work, large-scale experiments on ping-pong-ball avalanches are investigated. In one situation, channeled flows with up to 6000 balls are produced. Another set-up is the open, three-dimensional flow over the landing track of a ski-jump field, using up to 300 000 ping-pong balls. The measurements focus on the internal velocity distribution, of the balls as well as of the air. A video camera positioned above the flow allows the measurement of the location and distance of a single ball, which finally leads to its velocity. Different profiles in the head and tail as well as other flow properties are obtained. With vertically placed lubes, in and above the flow, the open ends pointing towards the ground, the static pressure depression induced by the air flow is measured and leads to qualitative air-velocity profiles in and above the tail of the ping-pong-ball avalanches.