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1.
INTRODUCTIONPlanewakeflowisonetypeoffreeshearflowandexistswidelyinnatureandmanyengi neeringsystems.Tounderstandthekineticchar acterofthelarge scalecoherentvortexstructuresandparticledispersioninplanewakeflowishelpfulforimprovingmanyprocessesinenergyengineering,chemicalengineeringandmaterialengineering .LargeeddysimulationinvolvesbothdirectsimulationandReynolds averagedapproaches.MethodshavebeendevelopedinrecentyearstosolvetheproblemofinstantaneousgasflowfieldandtosimulatehighReynoldsnumb… 相似文献
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INTRODUCTION Turbulent gas-particle flows are frequently found in natural phenomena and industrial processes.Cases of cylinders in cross flows with particles occur in heat exchange equipment,including the convective zone of a fluidized-bed combustor,and in the primary superheaters,reheaters,and economizers of coal-fired boilers.Coherent structures often occur in the above-mentioned gas-particle flow,and have great effect on such different systems,while some features of tur-bulent multiphas… 相似文献
3.
Gas-solid two-phase turbulent plane jet is applied to many natural situations and in engineering systems. To predict the particle
dispersion in the gas jet is of great importance in industrial applications and in the designing of engineering systems. A
large eddy simulation of the two-phase plane jet was conducted to investigate the particle dispersion patterns. The particles
with Stokes numbers equal to 0.0028, 0.3, 2.5, 28 (corresponding to particle diameter 1 μm, 10μm, 30μm, 100μm, respectively)
inRe=11 300 gas flow were studied. The simulation results of gas phase motion agreed well with previous experimental results.
And the simulation results of the solid particles motion showed that particles with different Stokes number have different
spatial dispersion; and that particles with intermediate Stokes number have the largest dispersion ratio.
Project (No. G19990222) supported by the Special Funds for Major State Basic Research of China 相似文献
4.
XIE Ming-liang LIN Jian-zhong XING Fu-tang 《浙江大学学报(A卷英文版)》2007,8(2):275-284
INTRODUCTION Turbulent particulate flows occur in many in-dustrial applications, such as in pneumatic transportof particulates, cyclone separators and chemical re-actors. The particles suspended in fluid play a role inthe turbulence modulation, which has been known forseveral years. The observation that adding dust to airflowing in turbulent motion through a pipe can ap-preciably reduce the resistance coefficient was re-ported by Sproull (1961). The observation can beexpressed as saying … 相似文献
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Laser Doppler Anemometer has been used to measure the flow field characteristics near the interface around a moving bubble in the presence of ultrafine particles. In order to model a moving bubble, the bubble was fixed into the counter-flow liquid by a metal mesh. Experimental materials are air and water, and the particles are complex oxidate powder. Experiments were carried out under the operating conditions: the liquid flow velocity u0 is 12.6 cm/s, the equivalent diameter de is 0.6 cm, the mass concentration of particle is 0.2%,the average particle diameter is about 10 nm and the density is 2 g/cm3. The velocity profiles of both frontal and tail-vortex areas were measured respectively. The experimental results show that the velocity fields are obviously changed in the existence of particles. In the frontal area of the bubble, both tangential and normal velocities decrease due to the presence of particles, but in tail vortex area, the tangential velocities increase remarkably, and normal velocities rise gradually from the center towards the fringe in the opposite tendency to that of no particles. The influences of flow field change in the presence of particles on gas-liquid mass transfer are analyzed and discussed. 相似文献
6.
Lattice Boltzmann method was used to numerically investigate the motion and orientation distribution of cylindrical and cubic particles in pipe flow with high concentration and high particle to pipe size ratio. The transient impulse model of 3D collisions between particles and between particle and wall is proposed. The numerical results are qualitatively in agreement with and quantitatively comparable to the experiment data. The results show that the increases of both the cylindrical particle to pipe size ratio and the particle aspect ratio decrease the rotation about all axes. All rotations of cubic particles decrease with increasing the particle concentration. The cubic particles, rotating more drastically in the flow with large Reynolds number, rotate faster than the cylindrical particles with the same size. The cylindrical particles align with the flow direction more obviously with decreasing Reynolds numbers. However, the orientations of cubic particles are spread all over the range with no significant difference in magnitude, and the Reynolds numbers have no obvious effect on the orientations of cubic particles. 相似文献
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INTRODUCTION A number of problems involve flows of gases orliquids over bluff bodies such as air flowing over carsand airplanes and wind blowing over bridges andbuildings. Many experiments or simulations havefocused on the above problems. In those phenomena,flows will not follow the solid bodies completely, butseparate from them and create wakes. The generationand shedding of large coherent vortex structures dueto flow separation make the bluff body flows complexand very difficult … 相似文献
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A numerical investigation was performed on the reduction of the fluid forces acting on the square cylinder in the laminar flow regime with a perforated plate. The effects of geometric parameters such as the distance between the square cylinder and the perforated plate on the wake of the square cylinder were discussed. Furthermore, the flow characteristics such as the drag coefficient, lift coefficient, Strouhal number and flow pattern were obtained. It can be concluded that the drag force of the square cylinder reduces to some extent due to the addition of the perforated plate. The flow structure varies when the perforated plate is located behind the square cylinder. Moreover, the recirculation zone augments with the increase of L/D, and the vortex trace on the upper and lower surface of the square cylinder moves gradually backwards until a stable recirculation zone formed between the square cylinder and the perforated plate. 相似文献
9.
对水处理中矿物胶体颗粒表面附着有机物分子的状态下的混凝过程进行了实验研究。结果表明,胶体颗粒表面附着有机物分子形态结构具有复杂性和多变特性,吸附在胶体颗粒表面的有机物分子的各种结构型式会引起胶体颗粒表面性质的改变,以及这些分子形态结构会对混凝过程形成影响,包括颗粒物的作用半径,胶体稳定性,颗粒物之间的絮凝机理及絮体结构变化。这对于理解有机物分子存在条件下的胶体混凝过程的复杂性具有重要的理论意义和指导实践作用。 相似文献
10.
Fu-you Tian Lian-feng Huang Li-wu Fan Hong-liang Qian Jia-xi Gu Zi-tao Yu Ya-cai Hu Jian Ge Ke-fa Cen 《浙江大学学报(A卷英文版)》2016,17(2):89-100
The pressure drop over a packed bed with sintered ore particles was studied experimentally. The sintered ore particles were characterized to determine their equivalent particle diameter, bed voidage, and sphericity. The pressure drop experiments were performed on unsorted and sieved particles with various size distributions for a superficial velocity up to 2.4 m/s, covering flow regimes from laminar to turbulent. It was shown that the Ergun equation underestimates the pressure drop for such highly irregular-shaped particles by about 40%. The measured modified friction factor was well correlated to a scaled Ergun equation, which was verified to be valid for the modified particle Reynolds number up to 12 000 toward design and optimization of vertically arranged sinter coolers for waste heat recovery. 相似文献
11.
In this paper, to study the characteristics of the flow in a laminar regime, an immersed boundary-lattice Boltzmann flux solver (IB-LBFS) is applied to numerically simulate the unsteady viscous flows around two fixed and rotating circular cylinders in side-by-side arrangement. This method applies finite volume discretization to solve the macroscopic governing equations with the flow variables defined at cell centers. At the cell interface, numerical fluxes are physically evaluated by a local lattice Boltzmann solution. In addition, the no-slip boundary condition is accurately imposed by using the implicit boundary condition-enforced immersed boundary method. Due to the simplicity and high efficiency of IB-LBFS on non-uniform grids, it is suitable for simulating fluid flows with complex geometries and moving boundaries. Firstly, numerical simulations of laminar flow past two side-by-side cylinder are performed with different gap spacings at Reynolds numbers of 100 and 200. The simulation results show that a small gap spacing induces a biased flow and forms an irregular big wake behind two cylinders at a low Reynolds number. As the gap spacing increases, an in-phase or anti-phase flow is observed. Then, the effects of the main important parameters on flow characteristics are analyzed for flow past two side-by-side rotating cylinders, including the rotational speed, Reynolds number, and gap spacing. As the rotational speed is increased, the numerical results illustrate that unsteady wakes are suppressed and the flow becomes steady. As the gap spacing is increased, two separate vortex streets behind each cylinder are formed with a definite phase relationship and single shedding frequency. 相似文献
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刘娟 《湖北广播电视大学学报》2011,31(11):159-160
实验测试了氨基磺酸系高效减水剂AH溶液的表面张力、AH在水泥颗粒表面的吸附量及ξ电位,结果表明：AH能够减小溶液表面张力,使分散体系的自由能降低;它在水泥颗粒表面呈环圈及尾状吸附,产生较大的立体空间位阻;掺AH的水泥粒子表面ξ电位绝对值较大,水泥颗粒间存在着较强静电斥力。这些均使得AH具有良好分散作用。此外,AH分子结构中存在的极性基团与水分子间的氢键缔合,在水泥粒子表面形成的溶剂化水膜的润滑,也对AH分散起到一定的加强作用。 相似文献
13.
以丙烯酸-2-羟丙酯(HPA)为接枝剂,采用种子乳液原位聚合法合成了聚氨酯接枝聚丙烯酸酯(W PUA)复合分散体.通过傅立叶红外光谱(FT IR)、凝胶渗透色谱(GPC)和粒径测定及透射电镜观察(TEM)对W PUA复合分散体的结构、分散体的粒子大小及形态进行了研究.结果表明,以HPA为接枝剂,通过种子乳液原位聚合可以实现PA在W PU上的接枝,接枝率约为70%;分散体平均粒径约为103 nm;TEM显示分散体粒子具有反相核壳结构. 相似文献
14.
A cold-model vertical multi-tube circulating fluidized bed evaporator was designed and built to conduct a visualization study on the pressure drop of a liquid-solid two-phase flow and the corresponding particle distribution.Water and polyformaldehyde particle (POM) were used as the liquid and solid phases,respectively.The effects of operating parameters such as the amount of added particles,circulating flow rate,and particle size were systematically investigated.The results showed that the addition of the particles increased the pressure drop in the vertical tube bundle.The maximum pressure drop ratios were18.65%,21.15%,18.00%,and 21.15%within the experimental range of the amount of added particles for POM1,POM2,POM3,and POM4,respectively.The pressure drop ratio basically decreased with the increase in the circulating flow rate but fluctuated with the increase in the amount of added particles and particle size.The difference in pressure drop ratio decreased with the increase in the circulating flow rate.As the amount of added particles increased,the difference in pressure drop ratio fluctuated at low circulating flow rate but basically decreased at high circulating flow rate.The pressure drop in the vertical tube bundle accounted for about 70%of the overall pressure drop in the up-flow heating chamber and was the main component of the overall pressure within the experimental range.Three-dimensional phase diagrams were established to display the variation ranges of the pressure drop and pressure drop ratio in the vertical tube bundle corresponding to the operating parameters.The research results can provide some reference for the application of the fluidized bed heat transfer technology in the industry. 相似文献
15.
SAENGHAENGTHAM Nida KANONGCHAIYOS Pizzanu 《浙江大学学报(A卷英文版)》2006,7(7):1225-1232
INTRODUCTION Collision detection is an important task in many fields such as robotics, computer games, computa- tional geometry (Gottschalk et al., 1996), computer simulation, virtual reality, etc. Most collision detec- tion algorithms work efficiently only with solid and rigid objects, so collision detection between de- formable objects is a challenge. A number of re- searches on non-rigid objects are proposed such as cloth simulation (Bridson et al., 2003; Teschner et al., 2004) and bi… 相似文献
16.
Particle image velocimetry （PIV） experimental results of wake flow structure of a NACA0012 airfoil with small attack angle mounted above water surface are introduced.The experiment was carried out in a small-scale wind-wave tunnel.The diameter of wind-wave tunnel test section is 1.7 m （long） × 0.4 m （width） × 0.4 m （height）.The flow fields around the airfoil were measured under four diffierent conditions by varying the distance between the airfoil and the water surface.The attack angle of the airfoil was kept 10- during the experiment.For each experimental condition,the time series of particle images was captured to calculate continuous evolution of the velocity fields.The velocity fields were ensemble averaged to get the statistic parameters such as mean velocity and vorticity.Typical instantaneous velocity fields for each case are introduced to show the basic flow structure of wind surface flow separation.The aerodynamic loads acting on the airfoil are analyzed qualitatively according to the mean vorticity distribution in the flow field based on the theory of vorticity aerodynamics.The results indicate that the flow structures and drag/lift force of the airfoil alter remarkably with the changing distance between the airfoil and water surface. 相似文献
17.
Impact of inert metal particles flow on aluminium plate 总被引：1，自引：0，他引：1
Inert metal explosive,a new kind of explosive,is a mixture of high explosive and inert metal particle.When this kind of explosive is detonated,an inert metal particle flow will be formed by the ex-plosive product driving.To determine the characteristics of the movement of the metal particle flow,a series of aluminium plates were designed to be the targets on which the metal particle flow impacted.The test result was presented and a numerical model was set up to analyze the impact of the high speed inert metal particles on aluminium plate.Based on the numerical analysis,the relationship between the characteristic of the mark on the target plate and the initial condition of the inert metal particles was pro-posed.From the analysis of the impact on target plates,more information about the movement of the metal particles could be reconstructed. 相似文献
18.
在25℃下,以0．5 g/min的加料速度,用一种Ludox硅溶胶作为种子,在氨、水和乙醇的混合溶液中通过水解正硅酸乙酯（TEOS ）生长出单分散的SiO2颗粒,研究了滴加TEOS时间对颗粒生长的影响,以及滴加结束后时间对颗粒生长的影响。通过透射电镜（TEM ）分别对样品的结构及形貌尺寸进行了表征和分析。结果显示,此方法制得的样品粒径分布范围窄、分散性好。 相似文献
19.
基于有限体积方法,对嵌入式行星螺杆挤出机内流场进行了三维等温数值模拟。通过简化的物理模型来模拟螺杆的几何结构,使用用户自定义程序设定了行星螺杆运动的边界条件。分析了挤出机螺槽内压力和速度的分布;使用粒子追踪技术观察了螺杆内流体运动轨迹和粒子分布规律;对粒子在螺杆内的停留时间分布进行了统计。结果表明行星螺杆对流体运动产生了周期性扰动。初始位置在一起的两个粒子,终点位置却相距很远。示踪粒子的具有对初始敏感的混沌特性,粒子的运动轨迹具有无序性,说明流体存在着混沌效应。 相似文献
20.
A method was presented to implement the detecting and tracking of moving targets through omnidirectional vision.The method combined optical flow with particle filter arithmetic.in which optical flow field was used to detect and locate moving targets and particle filter was used to track the detected moving objects.According to the circular image character of omnidirectionaI vision.the calculation equation of optical flow field and the tracking arithmetic of particle filter were improved based on the polar coordinates at the omnidirectional center.The edge of a randomly moving object could be detected by optical flow field and was surrounded by a reference region in the particle filter.A dynamic motion model was established to predict particle state.Histograms were used as the features in the reference region and candidate regions.The mutual information(MI)and Gaussian function were combined to calculate particle weights.Finally,the state of tracked object was computed by the total particle states with weights.Experiment results show that the proposed method could detect and track moving objects with better realtime performance and accuracy. 相似文献