ATLAS potential for elliptic flow measurements in Pb+Pb collisions at LHC

Study of particle azimuthal anisotropies, quantified by coefficients of the Fourier decomposition of the azimuthal angle distributions, has emerged as an important tool to probe the early stages of nucleusnucleus collisions. In this paper the ATLAS capability of measuring elliptic flow, the second Fourier coefficient, is presented. It is shown that various analysis techniques can be applied for different combinations of the detector sub-systems. A systematic comparison of various analysis methods is also shown.     

Azimuthal anisotropy of photon and charged parti cle emissionin 208Pb + 208Pb collisions at 158 $\ cdot A$ GeV/ c

The azimuthal distributions of photons and charged particles with respect to the event plane are investigated as a function of centrality in ²⁰⁸Pb + ²⁰⁸Pb collisions at 158 GeV/c in the WA98 experiment at the CERN SPS. The anisotropy of the azimuthal distributions is characterized using a Fourier analysis. For both the photon and charged particle distributions the first two Fourier coefficients are observed to decrease with increasing centrality. The observed anisotropies of the photon distributions compare well with the expectations from the charged particle measurements for all centralities.Received: 22 May 2004, Revised: 14 April 2005, Published online: 4 May 2005PACS: 25.75.Dw     

Laser Diffraction – Unlimited?

Within the past 20 years, particle size analysis with laser diffraction (LD) has been subject to rapid development, extending the size range stepwise from 1–200 μm to about 0.1–3500 μm. The limits of LD are discussed in terms of light sources, the influence of the beam diameter, special Fourier optics and a new detector design. It is shown that the size range is not only restricted by the wavelength of the laser and the transmission limits of the medium. Its extension is mainly related to improvements in the measurement of the angular intensity distribution. Influences from stability and flow dominate on the coarse side of the measuring range. On the fine side, the spatial extension of aerosols and the resulting demand for extended working distances can be covered only in a parallel laser beam. Extended Fourier optics in combination with an adapatable beam expansion technique and a detector with virtual borders between semicircular elements overcome the existing limits and extend the size range to a lower limit of about 0.05 μm and an upper limit above 10 mm. The sensititivity limit of LD is approaching that of single particle counting techniques. For medical spray and inhaler applications, a 0.1% optical concentration can be converted to particle size distributions even for time-resolved analyses with sample intervals of a few milliseconds. The reproducibility of the sensor, with a standard deviation typically much less than 0.5%, is no longer the limiting factor. The reproducibility of the results is mainly dominated by the reproducibility of sampling, sample splitting, dispersion and the contamination of the optical path. The latter can be improved by the control of flow, especially for in-line and inhaler applications.     

Multiplicity distributions of charged hadrons at AGS, SPS and RHIC

It is found that Collective Flow Model (CFM) which can successfully analyze charged particle distributions at AGS and lower SPS (less than 20 GeV/n), fails to analyze that of RHIC. The tail of distribution of charged particle at RHIC has a jump away from the collective model calculation as the energy increase. Thermalization Component Model (TCM) is presented basing on collective flow to study the multiplicity distributions at RHIC in this paper. It is realized that the limitation of phase space of collective flow can denote that of thermalization region. By comparing the contributions of particle productions from thermalization region at different energies and different centrality, we can deep our study on the feature of collective movement at RHIC.     

The Characterisation of Particles Using the Settling Rate dependent movement in two phase flows

The drawback of conventional sedimentation methods, mainly their extremely long sedimentation time for small particles, can be overcome in two phase flow systems. In this paper several principles which permit the rapid determination of settling rate distributions are discussed. Settling rate distributions can be determined from the accelerated particle movement in a flow of constant velocity at low and high solids concentrations. Another system uses accelerated flow at low solids concentrations. The best utilisation of settling rate applications have socalled cross flow systems as set up in a stagnation point flow, in a flow round a bend, or in the decelerated particle movement perpendicular to a flow of constant velocity.     

稠密气固流动中颗粒聚集的定量评价

本文提出了定量评价稠密两相流动中颗粒聚集现象的参数和方法:用碰撞频率的大小估计颗粒聚集的强弱;用颗粒体积分数的标准偏差评价流场中颗粒分布的不均匀程度;用颗粒分布的相关系数衡量流动的相似性;用颗粒体积分数的概率分布和颗粒分布曲线描述流场细节;用高密集区域颗粒数目比例和稀疏区域面积比例来反映流场的特征部分。     

Dynamic analysis of bubble-driven liquid flows using time-resolved particle image velocimetry and proper orthogonal decomposition techniques

Abstract  

An experimental study to evaluate dynamic structures of flow motion and turbulence characteristics in bubble-driven water flow in a rectangular tank with a varying flow rate of compressed air is conducted. Liquid flow fields are measured by time-resolved particle image velocimetry (PIV) with fluorescent tracer particles to eliminate diffused reflections, and by an image intensifier to acquire enhanced clean particle images. By proper orthogonal decomposition (POD) analysis, the energy distributions of spatial and temporal modes are acquired. Time-averaged velocity and turbulent kinetic energy distributions are varied with the air flow rates. With increasing Reynolds number, bubble-induced turbulent motion becomes dominant rather than the recirculating flow near the side wall. Detailed spatial structures and the unsteady behavior of dominant dynamic modes associated with turbulent kinetic energy distributions are addressed.     

Analysis of charged hadron multiplicity distributions at RHIC

It is demonstrated that with Heinz's collective flow model charged particle distributions at AGS and lower SPS energies (less than 20 GeV/n) ,can successfully be analyzed,but that the model fails for the RHIC data.Heinz's model calculation underestimates the tails of the charged particle distributions from RHIC,the discrepancy becoming bigger as the energy increases.To study the multiplicity distributions at RHIC we develop the so-cailed"Thermalization Component Model",which is based on Heinz's collective flow model.It is realized that the limitation of phase space of collective flow can be reflected in that of the thermalization region.By comparing the contributions of particle production from the thermalization regions at different energies and different centralities,we can deepen our understanding of the features of collective motion at RHIC.     

Anomalous dispersion in correlated porous media: a coupled continuous time random walk approach

We study the causes of anomalous dispersion in Darcy-scale porous media characterized by spatially heterogeneous hydraulic properties. Spatial variability in hydraulic conductivity leads to spatial variability in the flow properties through Darcy’s law and thus impacts on solute and particle transport. We consider purely advective transport in heterogeneity scenarios characterized by broad distributions of heterogeneity length scales and point values. Particle transport is characterized in terms of the stochastic properties of equidistantly sampled Lagrangian velocities, which are determined by the flow and conductivity statistics. The persistence length scales of flow and transport velocities are imprinted in the spatial disorder and reflect the distribution of heterogeneity length scales. Particle transitions over the velocity length scales are kinematically coupled with the transition time through velocity. We show that the average particle motion follows a coupled continuous time random walk (CTRW), which is fully parameterized by the distribution of flow velocities and the medium geometry in terms of the heterogeneity length scales. The coupled CTRW provides a systematic framework for the investigation of the origins of anomalous dispersion in terms of heterogeneity correlation and the distribution of conductivity point values. We derive analytical expressions for the asymptotic scaling of the moments of the spatial particle distribution and first arrival time distribution (FATD), and perform numerical particle tracking simulations of the coupled CTRW to capture the full average transport behavior. Broad distributions of heterogeneity point values and lengths scales may lead to very similar dispersion behaviors in terms of the spatial variance. Their mechanisms, however are very different, which manifests in the distributions of particle positions and arrival times, which plays a central role for the prediction of the fate of dissolved substances in heterogeneous natural and engineered porous materials.     

旋流泵无叶腔内盐析颗粒湍流脉动特性研究

盐析晶体颗粒脉动特性是研究湍流输运状态下盐析过程的重要问题之一.为探索泵内盐析晶体颗粒湍流脉动规律及其对液相流场的影响,采用相位多普勒粒子速度场仪对旋流式输送泵无叶腔内的盐析湍流流场进行了测量,通过对改变泵运行工况、运行介质温度后颗粒脉动速度分布情况的分析,初步掌握了无叶腔中盐析晶体颗粒的湍流脉动特性;同时,讨论了晶体颗粒存在对液相湍流结构的影响。实验结果表明,随着流量的增加,颗粒的周向、径向及轴向脉动速度相应提高;盐析颗粒脉动速度值随温度发生变化,较高温度时速度脉动也较大;在一定条件下,盐析晶体颗粒表现出抑制湍流的行为。     

An experimental investigation of three-dimensional particle aggregation using digital holographic microscopy

The tendency of particles to aggregate depends on particle-particle and particle-fluid interactions. These interactions can be characterized but it requires accurate 3D measurements of particle distributions. We introduce the application of an off-axis digital holographic microscopy for measuring distributions of dense micrometer (2 μm) particles in a liquid solution. We demonstrate that digital holographic microscopy is capable of recording the instantaneous 3D position of particles in a flow volume. A new reconstruction method that aids identification of particle images was used in this work. About 62% of the expected number of particles within the interrogated flow volume was detected. Based on the 3D position of individual particles, the tendency of particle to aggregate is investigated. Results show that relatively few particles (around 5–10 of a cohort of 1500) were aggregates. This number did not change significantly with time.     

浓淡燃烧器弯曲圆管内气固两相流动的试验研究

本文运用三维粒了动态分析仪（３Ｄ－ＰＤＡ）对竖直转水平弯管内气固两相流动特性进行了测量，得到了管内气相的速度分布以及颗粒的浓度分布；为进一步改善湾管的浓缩特性，在弯管入口处安装了一三角形滑块，对其管内的颗粒浓度分布也进行了侧量，并记录了弯管两侧的阻力特性。实验结果为人型电站锅炉燃烧器的设计和运行提供了依据。     

Comparison of four mobility particle sizers with different time resolution for stationary exposure measurements

Exposure to airborne ultrafine and nanoparticles has raised increased interest over the recent years as they may cause adverse health effects. A common way to quantify exposure to airborne particles is to measure particle number size distributions through electrical mobility analysis. Four mobility particle sizers have been subject to a detailed intercomparison study, a TSI Fast Mobility Particle Sizer (FMPS), a Grimm Sequential Mobility Particle Sizer (SMPS+C), and two TSI Scanning Mobility Particle Sizers (SMPSs), equipped with two different condensation particle counters (CPC). The instruments were challenged with either NaCl or diesel soot particles. The results indicate that the sizing of all tested instrument was similar with only the FMPS size distributions consistently shifted toward smaller particle sizes. The Grimm SMPS generally measured higher concentrations and broader distributions than the TSI instruments. The two Grimm DMAs agreed well with each other; however, the TSI SMPS results showed a reproducible dependence on the flow rates. While TSI and Grimm SMPS delivered consistent results for sodium chloride (NaCl) and diesel soot, the FMPS seemed to react differently to the changing particle source than the SMPSs, which may be caused by either the different morphology or particle size dependent effects. For NaCl particles, the FMPS delivered the narrowest distributions and concentrations comparable with TSI SMPSs, whereas for diesel soot, it delivered the broadest distributions and higher concentrations than TSI SMPSs.     

Particle Mass Loading Effect on a Two-Phase Turbulent Downward Jet Flow

The particle mass loading effect on the flow structure of a two-phase turbulent jet flow was studied. A particle mass loading ratio ranging from 0 to 3.6 was used as the control parameter. The polystyrene solid particles used had nominal diameters of 210 and 780 μm. The flow Reynolds number, which was based on the pipe nozzle diameter and the fluid-phase centerline mean velocity, was 2 × 10⁴ in the current test. A two-color laser Doppler anemometer (LDA), combined with the amplitude discrimination method and the velocity filter method, was employed to measure the mean velocity distributions for the particle and fluid phases, and the turbulent intensities and Reynolds stresses of the flow. The two-phase jet flow field was measured from the initial pipe exit to 90 D downstream. Another one-component He? Ne laser LDA system was also applied to obtain the energy spectra and temporal correlations of the two-phase jet flow.     

Rotational intermittency and turbulence induced lift experienced by large particles in a turbulent flow

The motion of a large, neutrally buoyant, particle freely advected by a turbulent flow is determined experimentally. We demonstrate that both the translational and angular accelerations exhibit very wide probability distributions, a manifestation of intermittency. The orientation of the angular velocity with respect to the trajectory, as well as the translational acceleration conditioned on the spinning velocity, provides evidence of a lift force acting on the particle.     

颗粒湍流扩散的数值模拟

1引言颗粒湍流扩散是气固两相流中的一个重要的研究课题,近年来,国外有大量文献报道这方面的工作。因为颗粒的湍流扩散的研究的一个基本问题就是湍流的描述,它一方面可以来检验湍流描述的正确性;另一方面,该问题是气固两相流理论中,特别是颗粒群轨道模型中一个难点。描述湍流大体上可分为两种方法。一是直接数值模拟方法（DNS）,J．B．Mclaughlin对管流内颗粒沉降的研究就基于直接数值模拟山,K．D．squires和J．K．Eaton对颗粒扩散的研究也基于DNS［2］,DNS一般只适用于低Reynolds数。另一方面,用随机方法来模拟湍流,该…     

Spatial anisotropy: a method to study anisotropic flow in heavy ion collisions

We introduce a method to study anisotropic flow parameter v<,n> as a collective probe to Quark Gluon Plasma in relativistic heavy ion collisions. The emphasis is put on the use of the Fourier expansion of initial spatial azimuthal distributions of participant nucleons in the overlapped region. The coefficients ε<,n> of Fourier expansion are called the spatial anisotropy parameter for the n-th harmonic. We propose that collective dynamics can be studied by v<,n>/ε<,n>. In this paper, we will discuss in particular the second (n=2) and the fourth (n=4) harmonics.     

Absorption and Scattering of Light by Highly Concentrated Two‐phase Flows

The spray cone emerging during an extended metal atomization process (called spray forming) has been investigated in order to quantify the influence of highly concentrated multiphase flows on phase‐Doppler‐anemometry (PDA) measurements. Using this non‐intrusive, optical measurement technique not only the local particle size and velocity distributions of the spray can be obtained but also additional information about the mass flux in the multiphase flow. Since standard phase‐Doppler systems can be easily applied to low concentrated particle systems (spherical particles with smooth surfaces and an optical transparent continuous phase taken for granted) the application of this measurement technique to highly concentrated multiphase flows is more complex. Both the laser light propagating from the PDA device to the probe volume and the scattered one going backward to the PDA receiving system are disturbed by passing the highly concentrated multiphase flow. The resulting significant loss in signal quality especially concerns the measurement of the smaller particles of the spray because of their reduced silhouette (in comparison with the bigger ones). Thus, the detection of the smallest particles becomes partially impossible leading to measurement of a distorted diameter distribution of the entire particle collective. In this study the distortions of the measured distributions dependent on the particle number concentration as well as on the path length of the laser light are discussed.     

Evaluation of char combustion models: measurement and analysis of variability in char particle size and density

Char samples representing a range of combustion conditions and extents of burnout were obtained from a well-characterized laminar flow combustion experiment. Individual particles from the parent coal and char samples were characterized to determine distributions in particle volume, mass, and density at different extent of burnout. The data were then compared with predictions from a comprehensive char combustion model referred to as the char burnout kinetics model (CBK). The data clearly reflect the particle-to-particle heterogeneity of the parent coal and show a significant broadening in the size and density distributions of the chars resulting from both devolatilization and combustion. Data for chars prepared in a lower oxygen content environment (6% oxygen by vol.) are consistent with zone II type combustion behavior where most of the combustion is occurring near the particle surface. At higher oxygen contents (12% by vol.), the data show indications of more burning occurring in the particle interior. The CBK model does a good job of predicting the general nature of the development of size and density distributions during burning but the input distribution of particle size and density is critical to obtaining good predictions. A significant reduction in particle size was observed to occur as a result of devolatilization. For comprehensive combustion models to provide accurate predictions, this size reduction phenomenon needs to be included in devolatilization models so that representative char distributions are carried through the calculations.     

Evaluating practical measurements of fire-induced vent flows with stereoscopic PIV

Stereoscopic particle image velocimetry (SPIV) was applied to a fire-induced doorway flow to provide the velocity field for computations of the mass flow rate of air into an enclosure. For a flow of uniform temperature and concentration, the technique met all of the requirements to provide the best estimate of the mass flow rate. Simultaneous measurements of vertical distributions of velocity and temperature were also conducted with conventional vent flow techniques, bi-directional probes and thermocouples. Correction factors for mass flow rate computations using the conventional techniques were determined based on comparisons to the SPIV results. An average correction factor of unity was determined for the bi-directional probe technique thus further confirming the utilization of velocity distributions acquired using the technique in mass flow rate computations. An average correction factor of 0.69 was determined for mass flow rates computed from vertical temperature distributions inside and outside the enclosure. This agrees with average correction factors determined in previous studies. The results from the present study suggest that the conventional techniques, which are practical and affordable for routine fire testing, may be applied with greater confidence for fires up to 500 kW.