风沙跃移运动发展过程及静电力影响的数值模拟

建立了描述风沙跃移运动发展过程以及风场一沙粒互馈机制的风沙跃移运动数值模型,模型中考虑了风场一沙粒之间酌耦合作用以及静电力的影响,同时风场是随时间变化的．模拟了风沙跃移运动从起始阶段至风沙流达到自平衡状态的整个发展过程所需的时间,起沙率与单宽输沙率随时间变化曲线,以及达到稳定后的单位面积输沙率沿高度分布以及贴地风速廓线的影响．计算结果表明,当沙粒平均带电量为60μC／kg时,计算所得的单宽输沙率以及输沙率沿高度分布与实验结果吻合得较好．     

风沙运动的沙粒带电机理及其影响的研究进展

土壤风蚀以及沙尘暴是人类面临的重大自然环境灾害之一,它直接关系着人类的生存环境和生活质量.许多国家和政府以及科学家们对此一直十分关注并开展了大量研究.由于大气和地表条件的多样性以及地表沙粒的运动与风场作用的相互耦合,导致风沙运动问题研究的复杂性.除此之外,伴随着对风沙运动机理的研究和对沙尘暴的观测,人们发现在风沙跃移运动和沙尘暴中的沙粒带有电荷并形成风沙电场.沙粒的运动不仅导致沙粒带电和风沙电场形成,而且也直接受到沙粒带电和风沙电场的影响.为了弄清风沙电的起因以及揭示其影响规律,研究人员对此进行了野外观测、实验室测量和理论推测等.本文将就这一问题重点介绍有关风沙运动中沙粒带电的机理、风沙电场分布规律、沙粒带电对风沙运动的微宏观物理量以及沙尘暴中沙粒带电对电磁波散射的影响等方面的实验和理论研究的基本概况和进展以及作者等人在此方面的研究工作.主要包含内容有:沙粒带电及其电场的基本实验测量,粒带电对风沙运动的影响,沙尘暴对电磁波衰减的影响研究以及有关风沙起电的机理研究等.同时,对这一研究领域中目前关注与存在的主要问题给予评述.图6参81      

Effects of g-jitter and radiation on three-dimensional double diffusion stagnation point nanofluid flow

The unsteady double diffusion of the boundary layer with the nanofluid flow near a three-dimensional(3 D) stagnation point body is studied under a microgravity environment. The effects of g-jitter and thermal radiation exist under the microgravity environment, where there is a gravitational field with fluctuations. The flow problem is mathematically formulated into a system of equations derived from the physical laws and principles under the no-slip boundary condition. With the semi-similar tran...     

The loss of stability of laminar flow in open channel and the mechanism of sand ripple formation

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Effect of ion‐slip current on the thermal instability of mixed connection in a boundary layer flow

Effect of ion‐slip current on the thermal instability in a boundary layer is studied. The criterion on the position marking the onset of longitudinal vortices is defined in the present paper. The results show that the onset position characterized by the Grashof number depends on the Prandtl number, the Reynolds number, the wave number, the Hall parameter, the ion‐slip parameter, and the Hartmann number. The flow becomes more stable as the magnetic field increases. However, the destabilizing effects are found on the flow when the Hall and ion‐slip currents are presented. The results of the present numerical prediction show reasonable agreement with the experimental data in the case of zero Hartmann number, ion‐slip parameter, and Hall parameter in the open literature. Copyright © 2011 John Wiley & Sons, Ltd.     

Carbon nanotubes on unsteady MHD non-Darcy flow over porous wedge in presence of thermal radiation energy

The thermal radiation energy is the clean energy with a much lower environmental impact than the conventional energy. The objective of the present work is to investigate theoretically the effect of copper nanoparticles and carbon nanotubes (CNTs) in the presence of base fluid (water) with the variable stream condition due to the thermal radiation energy. Single-walled carbon nanotubes (SWCNTs) in the presence of base fluid flow over a porous wedge play a significant role compared to those of copper nanoparticles on absorbing the incident solar radiation and transiting it to the working fluid by convection.     

Effect of particles on turbulent thermal field of channel flow with different Prandtl numbers

The direct numerical simulation(DNS) of heat transfer in a fully developed non-isothermal particle-laden turbulent channel flow is performed.The focus of this paper is on the modulation of the particles on turbulent thermal statistics in the particle-laden flow with three Prandtl numbers(P r = 0.71,1.5,and 3.0) and a shear Reynolds number(Reτ = 180).Some typical thermal statistics,including normalized mean temperature and their fluctuations,turbulent heat fluxes,Nusselt number and so on,are analyzed.The results show that the particles have less effects on turbulent thermal fields with the increase of Prandtl number.Two reasons can explain this.First,the correlation between fluid thermal field and velocity field decreases as the Prandtl number increases,and the modulation of turbulent velocity field induced by the particles has less influence on the turbulent thermal field.Second,the heat exchange between turbulence and particles decreases for the particle-laden flow with the larger Prandtl number,and the thermal feedback of the particles to turbulence becomes weak.     

Soliton-like thermal source forcing and singular response of atmosphere and oceans to it

IntroductionAsystemfrequentlyobservedingeophysicalfluidsthatislong_lived ,organized ,andalwaysofsteadylarge_amplitudeiscalledasolitonasaphenomenonwhichisseen ,forexample,asa“greatspot”intheJupiter’satmosphereandablockinghigh’ssituationintheatmosphereofourplanetary[1].Inthenonlinearforcing_dissipativesystemsoftheatmosphereandoceansthesolitonisbothaspecialandanessentialentity .Onadynamicbasis,itcanbeviewedapproximatelyasaproductwhenbalanceisreachedbetweenlineardispersionandnonlinearsteepness…     

Effects of thermal radiation on MHD viscous fluid flow and heat transfer over nonlinear shrinking porous sheet

This paper investigates the effects of thermal radiation on the magnetohy-drodynamic (MHD) flow and heat transfer over a nonlinear shrinking porous sheet. The surface velocity of the shrinking sheet and the transverse magnetic field are assumed to vary as a power function of the distance from the origin. The temperature dependent viscosity and the thermal conductivity are also assumed to vary as an inverse function and a linear function of the temperature, respectively. A generalized similarity transformarion is used to reduce the governing partial differential equations to their nonlinear coupled ordinary differential equations, and is solved numerically by using a finite difference scheme. The numerical results concern with the velocity and temperature profiles as well as the local skin-friction coefficient and the rate of the heat transfer at the porous sheet for different values of several physical parameters of interest.     

水流损失和热补偿共同作用对增强型地热系统(EGS)产能影响的研究

基于青海共和盆地-3705m地热田实测数据,结合流固耦合传热理论并运用Comsol软件,建立了离散型裂隙岩体流体传热模型。考虑水流损失和热补偿共同作用,模拟得到了开采过程中上、下岩层(盖层和垫层)为绝热不渗透、传热不渗透、渗透传热时,储层(上、下岩层和压裂层)温度场的变化特征,分析了产出流量、水流损失、产出温度、产热速率的变化规律。研究结果表明:采热过程中产出流量始终小于注入流量;产出流量增幅速率先增大后减小,最后趋于稳定,前3a产出流量增幅超过总增幅量的3/4;忽略水流损失,将高估产热速率,采热初期甚至达到考虑水流损失时产热速率的3倍以上;考虑水流损失,产热速率呈先快速上升再趋于稳定后逐渐下降的趋势,最优开采时间为3a^11a;研究上、下岩层对产出温度的影响,仅考虑传热,采热寿命延长5.43%,同时考虑渗流传热时,采热寿命延长2.71%;采热前9a,水流损失占主导作用,即流入上、下岩层水流损失对产热速率的影响高于热补偿效应,开采10a后,热补偿效应占主导作用;同时考虑水流损失和热补偿效应得到的产热速率变化规律与实际工程更为符合,建议选择低渗透能力的上、下岩层延长增强型地热系统(EGS)运行时间。     

大体积混凝土热学参数反分析新方法

基于线性传热理论 ,对大体积混凝土“气温变化 -表层温度响应”进行了研究。将单调变化的环境温度以较小的时间步长分段线性化 ,利用叠加原理 ,提出了混凝土热学参数反分析的新方法。利用 40 0 mm× 40 0 mm×2 2 0 mm混凝土块进行室外模型试验。在给定的临界扰动贡献率下 ,将实测资料区分为有效扰动与无效扰动 ,得到了混凝土的热学参数 ,验证了该方法的可行性。该方法具有测点数量少、测量时间短等优点 ,还可以同时得到导温系数与混凝土 -空气热交换系数 ,特别适合在反馈设计中应用     

Investigation of Coulomb force effects on ethylene glycol based nanofluid laminar flow in a porous enclosure

Forced convection heat transfer of ethylene glycol based nanofluid with Fe_3O_4 inside a porous medium is studied using the electric field. The control volume based finite element method(CVFEM) is selected for numerical simulation. The impact of the radiation parameter(R_d), the supplied voltage(?φ), the volume fraction of nanofluid(?), the Darcy number(Da), and the Reynolds number(Re) on nanofluid treatment is demonstrated. Results prove that thermal radiation increases the temperature gradient near the positive electrode. Distortion of isotherms increases with the enhance of the Darcy number and the Coulomb force.     

Effect of particle degradation on electrostatic sensor measurements and flow characteristics in dilute pneumatic conveying

Vigorous particle collisions and mechanical processes occurring during high-velocity pneumatic conveying often lead to particle degradation. The resulting particle size reduction and particle number increase will impact on the flow characteristics, and subsequently affect the electrostatic type of flow measurements. This study investigates this phenomenon using both experimental and numerical methods. Particle degradation was induced experimentally by recursively conveying the fillite material within a pneumatic pipeline. The associated particle size reduction was monitored. Three electrostatic sensors were embedded along the pipeline to monitor the flow. The results indicated a decreasing trend in the electrostatic sensor outputs with decreasing particle size, which suggested the attenuation of the flow velocity fluctuation. This trend was more apparent at higher conveying velocities, which suggested that more severe particle degradation occurred under these conditions. Coupled computational fluid dynamics and discrete element methods (CFD–DEM) analysis was used to qualitatively validate these experimental results. The numerical results suggested that smaller particles exhibited lower flow velocity fluctuations, which was consistent with the observed experimental results. These findings provide important information for the accurate application of electrostatic measurement devices in pneumatic conveyors.     

液体火箭爆炸地面有害气体生成与扩散分析

建立了自燃液体推进剂运载火箭爆炸时地面残余推进剂蒸发模型和产生的有害气体在大气中的扩散模型,给出了N2O4/UDMH液体推进剂爆炸产生的地面推进剂残留量、推进剂污染区直径、大气环境中地面残余N2O4和UDMH推进剂蒸发速率等参数的实验结果。利用该理论模型对大型运载火箭发生意外爆炸事故产生的地面残余推进剂蒸发时间和形成的有害气体危害范围进行了估算。该理论模型可为航天发射场制定安全防护措施提供有用的评估方法。     

Thermophoresis and Brownian motion effects on boundary layer flow of nanofluid in presence of thermal stratification due to solar energy

The problem of laminar fluid flow,which results from the stretching of a vertical surface with variable stream conditions in a nanofluid due to solar energy,is investigated numerically.The model used for the nanofluid incorporates the effects of the Brownian motion and thermophoresis in the presence of thermal stratification.The symmetry groups admitted by the corresponding boundary value problem are obtained by using a special form of Lie group transformations,namely,the scaling group of transformations.An exact solution is obtained for the translation symmetrys,and the numerical solutions are obtained for the scaling symmetry.This solution depends on the Lewis number,the Brownian motion parameter,the thermal stratification parameter,and the thermophoretic parameter.The conclusion is drawn that the flow field,the temperature,and the nanoparticle volume fraction profiles are significantly influenced by these parameters.Nanofluids have been shown to increase the thermal conductivity and convective heat transfer performance of base liquids.Nanoparticles in the base fluids also offer the potential in improving the radiative properties of the liquids,leading to an increase in the efficiency of direct absorption solar collectors.     

Effect of the magnetic field on the pulsatile flow through a rigid tube

I.IntroductionThefunctionofanaPbliedmagneticfield\onhumanbodieshasbeenknownandservedasakindofthemedicaltreatmentforalongtime.ThemagneticstoneusedasamedicineisrdeordedinShennongMaterlbMedica,'which.isthefirstChinesemedicinebookandwaswrittenin200A.D..ItwasalsorecordedtyancientGreecethatholdingmagneticstQnesinhandsandfeetcouldrelievethepainandspasml'l.However,beinglimitedbythelevelQfproductionandmedicaltreatmentsatthattime,themagnetictreatmentwasmainlyusedforlocallydephlogisticating,relievin…     

Approximate solutions for the problem of liquid film flow over an unsteady stretching sheet with thermal radiation and magnetic field

The proposed method is based on replacement of the unknown function by a truncated series of the shifted Legendre polynomial expansion. An approximate formula of the integer derivative is introduced. Special attention is given to study the convergence analysis and derive an upper bound of the error for the presented approximate formula. The introduced method converts the proposed equation by means of collocation points to a system of algebraic equations with shifted Legendre coefficients. Thus, after solving this system of equations, the shifted Legendre coefficients are obtained. This efficient numerical method is used to solve the system of ordinary differential equations which describe the thin film flow and heat transfer with the effects of the thermal radiation, magnetic field, and slip velocity.     

Mathematical Analysis of the Effect of Sedimentation and Compaction on Steady Transport Profiles in Sediments

Based on fundamental principles transport equations are derived for components in sediment layers. These differ from the usual formulation by the fact that compaction of sediments is explicitly considered. Compaction without doubt plays a significant role in the processes of early diagenesis. As an effect of compaction changing porosity can be observed in sediment profiles. In the paper analytical solutions are derived for cases in which porosity logs show an exponential shape. Comparison with those solutions, which are obtained for the constant porosity (i.e., no compaction) situation, show the relevance of the theoretically rigorous formulation, which is therefore recommended for implementation in computational models.     

非爆炸且不可还原农用硝酸铵热分解反应动力学的研究

利用加速度量热仪分别对普通硝酸铵和非爆炸且不可还原农用硝酸铵的绝热分解过程进行分析,分析结果通过动力学模型编程在微机控制系统上进行数据分析处理,得到了绝热分解温度与压力随时间的变化曲线、自加热速率随温度的变化曲线、准速率常数随温度的变化曲线、最大温升速率所需时间随温度的变化曲线,计算了分解动力学参数表观活化能、指前因子、不可逆温度和自加速分解反应温度。所有实验结果都表明,非爆炸且不可还原农用硝酸铵具有良好的热稳定性、安全性。