燃气单钝体绕流流场特性的数值模拟研究

应用基于有限体积法的FLUENT6.1计算软件对管道中单钝体的燃气绕流现象进行了仿真研究,即对实现管道燃气流量计量的DN200mm新型宽量程流量计的流场进行了数值模拟,就燃气计量管道中漩涡发生体的漩涡脱落频率与实测数据进行了比较。结果表明,数值计算结果与实测结果具有很好的一致性,从而提出了在新型燃气流量计的研制中可以应用数值模拟方法来优化流量计结构设计的结论。     

Numerical investigation of effects of particle shape on dispersion in an isotropic turbulent flow

To investigate the effects of particle shape on the dispersion in an isotropic turbulent flow, herein two direct numerical simulations are performed. The six degrees of freedom motion of spherical and spheroidal particles in a vertical uniform flow and a gas-particle two-way isotropic turbulent flow. The former, which is investigated using a numerical simulation with the Arbitrary Lagrangian-Euler (ALE) method, shows that a spheroidal particle travels with rotating and oscillating motions, which significantly affect the pressure and the friction force on the particle’s surface. The trend of the fluid force acting on the spheroidal particle’s surface also oscillates and differs from that on a spherical particle. The time variation of the fluid force on the spheroidal particle is modeled in the $C_D$ equation, which has a sine curve’s PDF relation with ${\mathit{Re}}_p$ and the particle’s maximum and minimum $C_D$ values. The latter simulation examines the effects of the particle shape on the dispersion with the motion model developed above. The particle’s dispersion behavior, which is analyzed by the statistical variable D and the Radial Distribution Function (RDF), shows that the dispersion motion is markedly affected by particle’s sphericity, especially for particles with a relatively small sphericity. The results suggest that this difference can influence ignitability, flammability, and the concentration of combustible gases released by particles, and requires further study.     

蒸发器流程布置的数值模拟研究与分析

基于湿球温度效率法,建立了蒸发器的稳态分布参数模型,分析了三种不同流路布置蒸发器的换热性能,并与前人的实验研究结果进行对比,计算所得的换热量与试验值的最大偏差为9．44％,说明该模型切实可行。运用该模型计算并分析了六种不同流路布置蒸发器的流动和换热特性,结果表明：逆流布置蒸发器换热最好,错流其次,顺流最差。各种流路布置方案管外迎风面风速不变时,随着管内冷媒流量的增大,管内压降、总换热景、显热换热量、潜热换热量均增大,但潜热所占比重增大。管内冷媒流量保持不变,蒸发器迎风面风速增大时,总换热量、显热换热量均增大,潜热换热量、压降、吸湿系数均减小;当风速增大到一定程度时,蒸发器换热量、压降的变化都趋于平缓。同时,在蒸发器流路布置中,重力的影响不可忽略。研究结论为蒸发器流程布置的优化设计提供了理论基础和指导方向。     

Numerical modeling on simultaneous removal of mercury and particulate matter within an electrostatic precipitator

A computational fluid dynamics (CFD) model coupled with gas-particle mass transfer, electrohydrodynamic (EHD) effect, electric field, particle motion and particle charging is established to advance the understanding of combined particulate matter precipitation and mercury capture within industrial electrostatic precipitators (ESPs). The comparisons between experimental data and numerical results demonstrate that this model can reasonably predict the mercury removal efficiency by powdered sorbent injection (PSI). The mechanism of simultaneous removal of mercury and particulate matter is then discussed in detail by considering the complex interactions among multi-physics. The influences of particle size, mercury concentration, particle injection rate and the EHD effect are investigated. The simulation results indicate that the mercury removal process is primarily controlled by the sorbent particle residence time, surface area and mass transfer rate. Accordingly, reducing the size of sorbent particles (activated carbon) can promote mercury removal efficiency while decreasing the particle collection efficiency. Increasing the initial mercury concentration and adsorbent mass loading also benefit mercury adsorption by influencing the mass transfer rate and the surface area. The EHD effect plays important roles in mercury removal and particle collection by means of altering the flow patterns and particle migration. The two mechanisms of in-flight and wall-bounded mercury adsorption affected by ionic wind are also evaluated and some interesting phenomena are observed.     

Numerical analysis of the general characteristics of stereological bias in surface liberation assessment of ore particles

In mineral processing, ground ore particles containing valuable minerals are commonly separated from the gangue by flotation. For efficient flotation, surface liberation, in which the particle surface is composed of one phase, is important. Surface liberation is commonly measured by two-dimensional (2D) measurement of particle sections of resin-mounted samples. Such 2D measurement is considered to result in a form of error called stereological bias; however, the stereological bias associated with surface liberation assessment has not been fully studied. A series of numerical simulations was here conducted, to investigate the influence of a particle’s texture (the 3D internal particle structure) and shape on such stereological bias. First, a total of 110 patterns of texture (10 patterns of grain size times 11 levels of grain content) were modeled, to determine the general characteristics of the stereological bias. Then, the influence on the stereological bias, of particle shape as represented by the aspect ratio (an index of global shape) and corrected sphericity (an index of surface roughness), was investigated. The results revealed that texture had the largest, aspect ratio the second largest, and corrected sphericity the smallest influence on the stereological bias in surface liberation measurement. Based on the results, it is suggested that a rough estimate of the stereological bias in the measurement of irregularly shaped real ore particles can be made from much simpler numerical models of spherical particles.     

突扩膨胀射流冲击换热与流动的数值模拟

采用大涡模拟模型对突扩膨胀射流冲击平板的传热特性及喷嘴内部流场进行数值模拟,得到不同进口Re数,不同膨胀比情况下喷嘴内部流场和射流冲击平板时的换热效果,分析了不同进口Re数、膨胀比E、冲击高度H/d对换热和流动的影响.研究表明,与直喷嘴进行对比,由于膨胀喷嘴射流与周围介质的掺混、渗透作用使射流的流速大大降低,最大速度偏离几何中心,使得换热效果减弱,对加热平板的冷却具有不对称性,但使得整个换热板的平均冷却效果更加均匀.     

Numerical simulations of blast loads and structural deformation from near-field explosions in air

Numerical simulations of air blast loading in the near-field acting on deformable steel plates have been performed and compared to experiments. Two types of air blast setups have been used, cylindrical explosive placed either in free air or in a steel pot. A numerical finite element convergence study of the discretisation sensitivity for the gas dynamics has been performed, with use of mapping results from 2D to 3D in an Eulerian reference frame. The result from the convergence study served as a foundation for development of the simulation models. Considering both air blast setups, the numerical results under predicted the measured plate deformations with 9.4-11.1%. Regarding the impulse transfer, the corresponding under prediction was only 1.0-1.6%. An influence of the friction can be shown, both in experiments and the simulations, although other uncertainties are involved as well. A simplified blast model based on empirical blast loading data representing spherical and hemispherical explosive shapes has been tested as an alternative to the Eulerian model. The result for the simplified blast model deviates largely compared to the experiments and the Eulerian model. The CPU time for the simplified blast model is however considerably shorter, and may still be useful in time consuming concept studies.All together, reasonable numerical results using reasonable model sizes can be achieved from near-field explosions in air.     

某过滤净化装置内部流场优化

使用CFD技术对某过滤净化装置内的流场均匀性进行优化研究,计算并分析不同工况下装置内部空气的流速,并利用正交试验方法设计模拟方案,研究不同导流板对装置内部流场的影响,确定最合理的导流板布置形式。采用正交试验对模拟结果进行分析,发现各因素影响水平从大到小分别为导流板数、导流板长度和送风量。在送风量一定的条件下,设置9块导流板,导流板长度为100 mm时装置内部的流场均匀性最好。     

Numerical simulation and design optimisation of an integrally-heated tool for composite manufacturing

Tooling design is crucial for the production of cost-effective and durable composite products. As part of the current search for cost reduction, integrally-heated tooling is one of the technologies available for ‘out-of-autoclave’ processing of advanced thermoset polymer composites. Despite their advantages, integrally-heated tools can suffer from uneven distribution of temperature, variability in heat flow rate and inconsistency in heating/cooling time. This research, therefore, investigates a number of design variables such as shape and layout of heating channels in order to improve the thermal performance of an integrally-heated tool. Design of Experiments (DoE) has been carried out using Taguchi’s Orthogonal Array (OA) method to set several combinations of design parameters. Each of these design combinations has been evaluated through numerical simulation to investigate heating time and mould surface temperature variation. The simulation results suggest that the layout of the channels and their separation play a vital role in the thermal performance. Signal-to-Noise (S/N) ratio and analysis of variance (ANOVA) have been applied to the results obtained to identify the optimal design combination of the integrally-heated tool. Statistical analysis reveals that the heating performance of an integrally-heated tool can be significantly improved when the channels’ layout is parallel. The shape of the channels has negligible effect and the distance between the channels should be determined based on the production requirement.     

Simulation analysis and engineering application of distribution characteristics about multi-stage atomization field for cutting dust in fully mechanized mining face

To improve the dust suppression efficiency of the external spray systems of shearers, a dust reduction method consisting of shearer external multi-stage atomization and dust removal fan was proposed. Computational fluid dynamics-based numerical simulation was combined with atomization experiments to analyze the migration and distribution of the cutting dust and multi-stage atomization field under airflow at the 2307 fully mechanized mining face of the Tangkou mine. The results show that with adding dust removal fan and multi-stage atomization points, the peak area of wind speed appeared on both sides of the shearer, and the wind speed was greater than 2.7 m/s, the dust concentration on the downside side of the shearer decreased, the spray coverage area increased significantly, and the droplet concentration at the shearer drum was the largest, exceeding 0.05 kg/m³. According to the research results, the multi-stage atomization arrangement of single-fluid water nozzles of shearer was put forward, and the field application was carried out. Compared with the engineering application results of the single-stage atomization dust suppression system, the total dust reduction rate of the synergistic effect of multi-stage atomization external spray with dust removal fan for the shearer is 87.12%, which is 38.59% higher than that of the conventional single-stage atomization dust suppression system.     

Numerical analysis of flow field and particle motion in a dynamic cyclonic selector

Computational Fluid Dynamics is employed to investigate the flow field and the fate of particles in a dynamic cyclonic classifier which is used to separate fine particles of dried sludge, produced as waste by pulp and paper-making processes. The cyclonic classifier is equipped with a rotating impeller, which improves the tangential flow, and a circular baffle, which distributes the inlet stream of gas and particles. Unsteady Reynolds-averaged Navier-Stokes equations are solved for the continuous phase, addressing the impeller motion though the Sliding Mesh approach, whereas Lagrangian tracking is employed for the particles. Surprisingly, the removal efficiency is found to be non monotonic with particle size, instead presenting a fish-hook shape. This is partly imputed to the presence of the circular baffle that promotes, in the bottom region of the cyclone, the formation of a nearly toroidal recirculation zone which entrains small particles, subsequently separated at the bottom. Moreover, too high inlet velocities were found to hamper the action of impeller rotation with a resulting detrimental effect on removal efficiency.     

Numerical investigation of influence of treatment of the coke component on hydrodynamic and catalytic cracking reactions in an industrial riser

A three dimensional gas-solid reactive flow model based on the Eulerian-Eulerian approach was used to simulate the hydrodynamic, heat transfer and catalytic cracking reaction within in a conventional Fluid Catalytic cracking (FCC) riser. A 12-lump kinetic model was used to represent the catalytic cracking reaction network. It was proposed a catalyst deactivation model as a function of the weight percentage of coke amount on the catalyst to replace the deactivation model dependent of the residence time. It was compared the effects of novel treatment for coke component (coke produced in the solid phase) with common treatment (coke produced in the gas phase) on the fluid dynamic and catalytic cracking. The results showed that the treatment for coke component affects radial distribution of coke mass flow. It also showed that the treatment for coke plays an important role in simulation with catalyst deactivation as a function of coke amount on catalyst.     

离心泵蜗壳效应数值模拟与分析

利用FLUENT软件结合有限元体积法和Navier—Stokes方程,通过数值模拟方法研究离心泵蜗壳内的二维流场情况。根据分析结果表明离心泵的蜗壳壁面随着与叶轮距离的增大,受到的冲击越小。蜗壳出口处的壁面位置会存在低压区,对离心泵的内部流场造成能量损耗。利用数值模拟的方法,对离心泵蜗壳的设计优化提供了理论依据。     

干冰升华气顶喷式冷冻室温度场的数值模拟与实验

对用干冰升华气体将长方体冷冻室内的温度控制在-18％下进行了数值模拟和实验。实验结果表明：当冷冻室内部温度场稳定后,除了冷冻室内四周的温度与设定值稍有偏差外（最大偏差为26．73％）,其它大部分都在设定的温度范围内,而数值模拟结果又和实验结果较好的吻合（偏差均小于20％）。以上结果表明,采用干冰升华气作为冷冻室的冷源基本上上可行的。此种型式的冷冻装置能够满足食品冷冻、冷藏的要求,也为干冰冷藏箱进一步的优化设计和大型化试验及应用提供了基础。     

分解炉内煤粉燃烧和CaCO3分解流场的数值模拟

针对国内某大型水泥高性能分解炉，基于Fluent软件，采用有限速率／涡耗散模型模拟了炉内煤粉燃烧和生料分解的湍动多相流场，给出了炉内速度矢量、温度、压力和组分分布，结果显示。炉内流动趋势合理，可为分解炉的研究提供参考。     

电磁流量计矩形与鞍状线圈磁场的数值仿真

讨论了电磁流量计矩形和鞍状线圈所产生磁感应强度的分布情况。运用毕奥-萨伐尔定律和叠加原理,通过数值仿真得到励磁线圈在测量管道内电极横截面上的磁场分布情况。提出磁感应强度的方向平行程度和大小均匀程度2个指标,并用其来判别感应磁场分布的均匀程度。依据以上2个指标,分别对不同尺寸的矩形和鞍状励磁线圈所产生的感应磁场进行计算分析和优化。     

某地铁站厅不同送回风方式的气流组织数值模拟和分析

地铁站厅公共区现今的空调设计,送回风方式主要有单送单回和两侧送中间回两种。根据不同的土建结构采用不同的方式。但由于空间比较大,送回风方式不合适可能会导致气流组织不良。本文以某地铁站厅为例,利用CFD方法,模拟和对比同一站厅不同送回风方式,并从各方面评价两种方式的效果,为地铁站气流组织的进一步研究和工程设计提供参考。     

A coupled numerical analysis of shield temperatures, heat losses and residual gas pressures in an evacuated super-insulation using thermal and fluid networks: Part I: Stationary conditions

This paper describes numerical simulations, using thermal networks, of shield temperatures and radiative and conductive heat losses of a super-insulated cryogenic storage tank operating at 77 K. Interactions between radiation and conductive heat transfer modes in the shields are investigated, by calculation of local shield temperatures. As a new method, fluid networks are introduced for calculation of stationary residual gas pressure distribution in the evacuated multilayer super-insulation. Output from the fluid network is coupled to the iterative thermal network calculations. Parameter tests concern thickness and emissivity of shields, degree of perforation, residual gas sources like desorption from radiation shields, spacers and container walls, and permeation from the inner container to the evacuated insulation space. Variations of either a conductive (thickness of Al-film on Mylar) or a radiative parameter (thermal emissivity) exert crosswise influences on the radiative or conductive heat losses of the tank, respectively.     

Effect of rotor cage's outer and inner radii on the inner flow field of the turbo air classifier

The effects of rotor cage's outer and inner radii on flow field of the turbo air classifier are comparatively analyzed by numerical simulation using ANSYS-FLUENT. The results of quantitative analysis show when the rotor cage's outer and inner radii are increased, the tangential velocity, radial velocity and upward axial velocity decrease in the annular region and near the entrance of the rotor cage. However, when the rotor cage's outer and inner radii are too large or too small, the tangential velocity and radial velocity will be fluctuated greatly. Moreover, the rotor cage's outer and inner radii directly influence the radial velocity distribution in the rotor cage channel. The rotor cage's outer and inner radii should not be too large or too small. Therefore, in the seven contrast rotor cage models, model 100–70 and 90–60 are selected to carry out the calcium carbonate classification experiments due to their small tangential velocity and radial velocity fluctuations and well-distribution in the rotor cage channel. The experimental results reflect the characteristics of the numerically simulated flow field in the classifier.