Characteristics of turbulence transport for momentum and heat in particle-laden turbulent vertical channel flows

The dynamic and thermal performance of particle-laden turbulent flow is investigated via direction numerical simulation combined with the Lagrangian point-particle tracking under the condition of two-way coupling, with a focus on the contributions of particle feedback effect to momentum and heat transfer of turbulence. We take into account the effects of particles on flow drag and Nusselt number and explore the possibility of drag reduction in conjunction with heat transfer enhancement in particle-laden turbulent flows. The effects of particles on momentum and heat transfer are analyzed, and the possibility of drag reduction in conjunction with heat transfer enhancement for the prototypical case of particle-laden turbulent channel flows is addressed. We present results of turbulence modification and heat transfer in turbulent particle-laden channel flow, which shows the heat transfer reduction when large inertial particles with low specific heat capacity are added to the flow. However, we also found an enhancement of the heat transfer and a small reduction of the flow drag when particles with high specific heat capacity are involved. The present results show that particles, which are active agents, interact not only with the velocity field, but also the temperature field and can cause a dissimilarity in momentum and heat transport. This demonstrates that the possibility to increase heat transfer and suppress friction drag can be achieved with addition of particles with different thermal properties.

Numerical Analysis on Nanoparticles-laden Gas Film Thrust Bearing

Nanoparticles can be taken as additives and added into various fluids to improve their lubricating performances. At present, researches in this area are mainly concentrated on the improvement effects of nanoparticles on the lubricating performances of liquid such as oil and water. Nanoparticles will also affect gas lubrication, but few related studies have been reported. Nanoparticles-laden gas film (NLGF) is formed when adding nanoparticles into gas bearing. Then, the lubricating performances of gas bearing including pressure distribution and load-carrying capacity will change. The variations of pressure distribution and load-carrying capacity in nanoparticles-laden gas film thrust bearing are investigated by numerical method. Taking account of the compressibility of gas and the interactions between gas and nanoparticles, a computational fluid dynamics model based on Navier-Stokes equations is applied to simulate the NLGF flow. The effects of inlet nanoparticles volume fraction and orifice radius on film pressure distribution and load-carrying capacity of the NLGF are calculated. The numerical calculation results show that both of the film land pressure and the maximum film pressure both increase when the nanoparticles are added into gas bearing, and the film pressures increase with the rising of the inlet nanoparticles volume fraction. The nanoparticles have an enhancement effect on load-carrying capacity of the studied bearing, and the enhancement effect becomes greater as the film thickness decrease. Therefore, nanoparticles can effectively improve the lubricating performance of gas bearing. The proposed research provides a theoretical basis for the design of new-type nanoparticles-laden gas film bearings.

Experimental Research on Dynamic Erosion of EPDM Insulation Subjected to Particle-Laden Flow

The instantaneous degradation of erosion surface of ethylene propylene diene monomer(EPDM)insulation subjected to the particle-laden flow in two operating conditions was measured by using a real-time X-ray radiography system.The images of its erosion state and dynamic ablation rate were obtained.And the charring-layer was analyzed by using SEM and energy spectrum.The experimental results indicate that the erosion rate of EPDM insulation layer impacted by low speed and low concentration particle flow is relatively small in the 1st second since the motor starting,but increases rapidly in 1 to 2.5 s,while the erosion rate of EPDM insulation layer impacted by high speed and high concentration particle flow increases rapidly in the 1st second;the ablation rate at the section eroded intensively by particle flow increases at first,then decreases,and goes to stabilization after 4.5 s;the higher speed and concentration particle flow are,the deeper particles get into charring layer,which lead to more thermal increment and thinner charring layer.

Effect of inertial particles with different specific heat capacities on heat transfer in particle-laden turbulent flow

The effect of inertial particles with different specific heat on heat transfer in particle-laden turbulent channel flows is studied using the direct numerical simulation（DNS） and the Lagrangian particle tracking method. The simulation uses a two-way coupling model to consider the momentum and thermal interactions between the particles and turbulence. The study shows that the temperature fields display differences between the particle-laden flow with different specific heat particles and the particle-free flow,indicating that the particle specific heat is an important factor that affects the heat transfer process in a particle-laden flow. It is found that the heat transfer capacity of the particle-laden flow gradually increases with the increase of the particle specific heat. This is due to the positive contribution of the particle increase to the heat transfer. In addition,the Nusselt number of a particle-laden flow is compared with that of a particle-free flow.It is found that particles with a large specific heat strengthen heat transfer of turbulent flow, while those with small specific heat weaken heat transfer of turbulent flow.

Effects of Rigid Vegetation on the Turbulence Characteristics in Sediment-Laden Flows

The effects of rigid vegetation on the turbulence characteristics were experimentally studied in the interior water flume. An ADV was used to determine the three dimensional turbulent velocities in clear water flow without vegetation, sediment-laden flow without vegetation, sediment-laden flow with submerged vegetation and sediment-laden flow with non-submerged vegetation. By experimental and theoretical analysis, the effects of rigid vegetation on the distribution of averaged velocities, turbulence intensities and Reynolds stress were summarized. In sediment-laden flow with submerged vegetation, the averaged stream wise velocities above the top of vegetation fit well with the log distribution low. The three-dimensional turbulence intensities increase from the bottom until they reach the maximum at the top of the vegetation. The method to calculate the shear velocity with the maximum of the Reynolds stress is recommended. In sediment-laden flow with non-submerged vegetation, the turbulence problems cannot be explained by theory of bed shear flow. The average velocities, turbulence intensities and Reynolds stress approximate uniformly distributed along vertical direction.

Two-phase micro-and macro-time scales in particle-laden turbulent channel flows

The micro- and macro-time scales in two-phase turbulent channel flows are investigated using the direct nu- merical simulation and the Lagrangian particle trajectory methods for the fluid- and the particle-phases, respectively. Lagrangian and Eulerian time scales of both phases are cal- culated using velocity correlation functions. Due to flow anisotropy, micro-time scales are not the same with the theo- retical estimations in large Reynolds number （isotropic） tur- bulence. Lagrangian macro-time scales of particle-phase and of fluid-phase seen by particles are both dependent on particle Stokes number. The fluid-phase Lagrangian inte- gral time scales increase with distance from the wall, longer than those time scales seen by particles. The Eulerian inte- gral macro-time scales increase in near-wall regions but de- crease in out-layer regions. The moving Eulerian time scales are also investigated and compared with Lagrangian integral time scales, and in good agreement with previous measure- ments and numerical predictions. For the fluid particles the micro Eulerian time scales are longer than the Lagrangian ones in the near wall regions, while away from the walls the micro Lagrangian time scales are longer. The Lagrangian integral time scales are longer than the Eulerian ones. The results are useful for further understanding two-phase flow physics and especially for constructing accurate prediction models of inertial particle dispersion.

Too Early to Celebrate bin Laden’s Death

More than being a victory of good against evil,media commentator Cheng Yi says the killing of Osama bin Laden has opened the way for retaliatory attacks from the terror group Al Qaeda who wilt no doubt use their leader’s death as a renewed call to arms.He argues that the irresponsible and unilateral way in which the United States went about the operation has stirred up further chaos and instabil-

Large-eddy Simulation of Near-field Dynamics in a Particle-laden Round Turbulent Jet

This article investigates the near-field dynamics in a particle-laden round turbulent jet in a large-eddy simulation （LES）. A point-force two-way coupling model is adopted in the simulation to reveal the particle modulation of turbulence. The particles mainly excite the initial instability of the jet and bring about the earlier breakup of vortex rings in the near-field. The flow fluc- tuating intensity either in the axial or in the radial directions is hence increased by particles. The article also describes the mean velocity modulated by particles. The changing statistical velocity induced by particle modulation implies the effects of modulation of the local flow structures. This study is expected to be useful to the control of two-phase turbulent jets.

HYDRODYNAMICS STABILITY OF BICKLEY JET WITH PARTICLE LADEN FLOW

The stability of Bickley jet with particle laden flow is investigated numerically. The stability characteristics are calculated for various Stokes numbers and particle concentrations. The results confirm the author＇s early calculations, which also shows that the numerical program is reliable. It is further shown that there is a critical value for the effect of Stokes number, which is about 2. The most damped mode occurs when Stokes number is of order of 10 for different particle concentrations and depends weakly on the wave number. The difference in the eigenfunctions and its derivatives between the particle-laden flow and the clean gas flow is insignificant for fine particles, while the difference for coarse particles is significant.

Water demand for ecosystem protection in rivers with hyper-concentrated sediment-laden flow

Sediment transport is one of the main concerns in a river system with hyper-concentrated flows. Therefore, the water use for sediment transport must be considered in study on the water demand for river ecosystem. The conventional methods for calculating the Minimum Water Demand for River Ecosystem (MWDRE) are not appropriate for rivers with high sediment concentration. This paper studied the MWDRE in wet season, dry season and the whole year under different water-and-sediment conditions in the Lower Yellow River, which is regarded as a typical river with sediment-laden flows. The characteristics of MWDRE in the river are analyzed. Firstly, the water demand for sediment transport (WDST) is much larger than the demands for other riverine functions, the WDST accounts for the absolute majority of the MWDRE. Secondly, in wet season when the WDST is satisfied, not only most of the annual incoming sediment can be transported downstream, but also the water demands for other river functions can be satisfied automatically, so that the MWDRE in wet season is identical to the WDST. Thirdly, in dry season, when the WDST is satisfied, the water demands for other river functions can also be satisfied, but the low sediment transport efficiency results in significant waste of water resources. According to these characteristics and aiming at decreasing sediment deposition in the riverbed and improving the utilization efficiency of water resources, hydrological engineering works can be used to regulate or control flow and sediment so that the sediment incoming in dry season can be accumulated and be transported downstream intensively and thus efficiently in wet season.

SIMULATION OF LOW-CONCENTRATION SEDIMENT-LADEN FLOW BASED ON TWO-PHASE FLOW THEORY

Low concentration sediment-laden flow is usually involved in water conservancy, environmental protection, navigation and so on. In this article, a mathematical model for low-concentration sediment-laden flow was suggested based on the two-phase flow theory, and a solving scheme for the mathematical model in curvilinear grids was worked out. The observed data in the Zhang River in China was used for the ver/fication of the model, and the calculated results of the water level, velocity and river bed deformation are in agreement with the observed ones.

REVIEW OF SOME RESEARCHES ON NANO-AND SUBMICRON BROWNIAN PARTICLE-LADEN TURBULENT FLOW

The study of nano- and submicron Brownian particle-laden turbulent flow has wide industrial applicability and hence has received much attention. The purpose of the present paper is to provide and review some researches in this field. The topics are related to the universality, particularity, complexity and importance of nano- and submicron Brownian particle-laden turbulent flow, the models of particle general dynamical equation, the collision behavior of particles. Finally, several open research issues are identified.

Firm Sells Bin Laden Toilet Paper

当今美国人对本·拉登的的仇恨不言而喻。于是,有一个美国商人跑出来幽它一默:在卫生纸上印上了本·拉登的漫画。作者称此类幽默为dark humor。文章末尾的一句话,又让我们对这为商人肃然起敬,假如,他真的能兑现的话。文中出现了crack一词,其含义费思量。美国传统词典对它的释义之一是:to tell(a joke),especially on impulse or in an effective manner/开玩笑尤指机智并有效地说(笑话)

Police Mistake Bearded Man for Bin Laden

文章首段,很有“噱头”,让人一惊:美国911事件的幕后策划者本·拉登被捕获了?第二段才揭开谜底:The man, who had a beard, was later released(释放)。本文的幽默一笔是:a crowd had gathered outside the police station Tuesday for a glimpse(一瞥)of the bin Laden look-alike.

高藻水处理过程中的加氯方式优化及藻源嗅味物质控制

针对高藻期水库水,研究了不同预氯化-消毒组合方式对常规工艺处理高藻水过程中污染物去除及藻源嗅味物质转化和去除的影响,以及预氯化-消毒组合方式对粉末活性炭吸附控制藻源嗅味物质效果的影响。结果表明,高藻水预氯化会使水中以非溶解态存在的2-甲基异莰醇(2-MIB)、土臭素(GSM)等藻源嗅味物质快速转化为溶解态。常规工艺能有效去除高藻水中的非溶解态嗅味物质,但对溶解态嗅味物质的去除效果十分有限;预氯化对常规工艺去除高藻水中2-MIB和GSM存在较大不利影响。粉末活性炭吸附能有效提升对2-MIB和GSM的去除效果,但预氯化会显著降低粉末活性炭吸附+常规工艺对2-MIB和GSM的总体去除效果。因此,对存在藻源嗅味物质的高藻水,不建议进行预氯化处理。

高焓流动中的可压缩颗粒两相流并行求解器:数值方法及其验证

在极端力学环境下可压缩点力颗粒两相流理论方程的基础上,提出一种基于动态链表数组的并行颗粒求解器,使其与可压缩流体求解器耦合。与基于欧拉坐标系的携带流体相不同,基于拉格朗日坐标系的求解器采用动态链表数组对弥散颗粒相进行内存分配,可以解决因使用全局数组解决拉格朗日/欧拉坐标系转换带来的弥散颗粒群内存利用率低和计算效率低下问题。最后对多物理效应的可压缩颗粒两相流求解器进行验证,并在马赫数渐进趋于零的情况下,对两个不可压缩槽道颗粒湍流标模进行验证。

中文阅读中的情绪词类型效应不受效价的调节:来自眼动的证据

本研究利用眼动追踪技术,将不同类型情绪词嵌入到同一句子框架,考察中文自然阅读中的情绪词类型效应及其与效价的关系。结果发现,情绪标签词注视时间显著长于情绪负载词,且这种注视差异不受情绪效价的调节。此外,对积极词的注视显著短于消极词,验证了积极效价的语义加工优势,支持了密度假说。结果表明,中文阅读中同样存在情绪词类型效应,且不论情绪效价如何,情绪标签词上情绪信息作用更为显著,更吸引读者注意且难以解离,表现出注意偏向优势。

满载运煤敞车超常低周疲劳刚柔耦合评估新方法

备用传力路径变化不确定性使准静态应变能成为决定平面心盘旁承接口耦合程度的最重要影响因素之一,既有方法丧失了小位移线弹假设的应用前提。根据这一相关性发现,提出了刚柔耦合疲劳损伤评估新方法。为了攻克散料运输铁路货车刚柔耦合仿真难题,采用了实体单元及边界共节点处理技术。在正常AAR5级谱和局部扭曲叠加谱激励输入下满载运煤敞车刚柔耦合仿真分析表明:上旁承运行荷载增大迫使车体结构扭曲产生不高于2 Hz的低频敏感响应。钩缓冲击座附近焊缝疲劳损伤评估结果与现场塑性破坏完全吻合。由于局部刚度不足,短竖梁补强设计也很难奏效。借鉴通用敞车耳板铆接的设计经验,合理制定了具有针对性的结构补强方案,使满载运煤敞车不会再发生上述塑性破坏。

磷素对含沙水流流体变异特性影响

[目的]为探明磷素对含沙水流流体变异特性的影响。[方法]采用自制双竖管流变仪,研究了磷素对不同浓度含沙水流流体类型、流变参数及流体发生变异的临界阈值的影响。[结果](1)磷素浓度、泥沙浓度及泥沙理化性质是影响含沙水流发生流体变异的主要因素。在25℃下,过磷酸钙浓度每增加0.1 g/cm^(3),黏滞系数和宾汉极限剪切力分别增加0.48~1.47 mPa·s和3.49~6.84 N/m^(2)。(2)随着磷素和泥沙含量的增大,含磷素的含沙水流由牛顿流体变异为宾汉流体。构建并验证了磷-泥沙水流黏滞系数和宾汉极限剪切力等流变参数的计算模型。(3)给出了磷-泥沙水流流体变异的临界浓度阈值。当磷素浓度从0增加至0.45 g/cm^(3)时,含沙水流的流体变异临界浓度阈值降低49%,说明磷素的存在加速了含沙水流的流体变异。[结论]磷素的增加使得侵蚀水流更容易由牛顿流体变异为宾汉流体,从而影响侵蚀流内部的能量耗散过程,研究结果为深入认识侵蚀污染水流的输移机制提供了新的科学基础。

生物炭对SBR法处理含盐生活污水的强化效果研究

为解决序批式活性污泥法(SBR)对含盐生活污水处理效率低的问题,考察了油菜秸秆生物炭(RSB_(650))投加对污染物去除效率和污泥性能的影响,探讨了应用于强化含盐生活污水处理效果的可行性和机制。结果表明,投加1.5~2.0 g/L RSB_(650)至受中低盐度(0.5%~1.0%)冲击的SBR系统,经11 d~50 d运行后COD、NH_(4)^(+)-N、TP去除率可恢复至90%以上,TN去除率可恢复至80%以上;而投加2.0 g/L RSB_(650)至受较高盐度(1.5%)冲击的SBR系统,上述污染物去除率仅能恢复至50%~80%左右。RSB_(650)优良的结构特性为SBR系统抵御盐度冲击提供了有利条件,用于强化中低含盐度生活污水处理效果具有良好的可行性。