Numerical simulation of micro-mixing in gas–liquid and solid–liquid stirred tanks with the coupled CFD-E-model

The coupled CFD-E-model for multiphase micro-mixing was developed,and used to predict the micro-mixing effects on the parallel competing chemical reactions in semi-batch gas–liquid and solid–liquid stirred tanks.Based on the multiphase macro-flow field,the key parameters of the micro-mixing E-model were obtained with solving the Reynolds-averaged transport equations of mixture fraction and its variance at low computational costs.Compared with experimental data,the multiphase numerical method shows the satisfactory predicting ability.For the gas–liquid system,the segregated reaction zone is mainly near the feed point,and shrinks to the exit of feed-pipe when the feed position is closer to the impeller.Besides,surface feed requires more time to completely exhaust the added H+solution than that of impeller region feed at the same operating condition.For the solid–liquid system,when the solid suspension cloud is formed at high solid holdups,the flow velocity in the clear liquid layer above the cloud is notably reduced and the reactions proceed slowly in this almost stagnant zone.Therefore,the segregation index in this case is larger than that in the dilute solid–liquid system.

猴子岩水库色玉滑坡涌浪灾害链CFD–DEM耦合数值模拟

滑坡涌浪是一种常见的地质灾害现象,由于滑坡体与水体之间存在复杂的流固耦合作用,使得传统的单一介质模型无法进行准确求解。为此,介绍一种基于计算流体力学方法(CFD)与离散单元法(DEM)的流固耦合模型CFD–DEM,采用计算流体力学方法(CFD)求解水体流动,采用离散单元法(DEM)模拟散粒体滑坡运动,充分利用不同计算模型的优势,对滑坡及涌浪演进过程进行数值模拟分析。首先,利用该耦合模型对Robbe–Saule开展的颗粒堆积体坍塌–涌浪试验进行了相同工况下的数值计算,从颗粒坍塌运动过程、涌浪高度演化过程等方面进行对比,结果表明模拟结果与试验结果吻合很好,验证了CFD–DEM流固耦合模型的有效性。然后,将该方法应用于四川省猴子岩水库色玉滑坡–涌浪灾害的演进过程分析,重现了该事件滑坡失稳运动、涌浪产生及传播、涌浪爬升、涌浪回流的全过程,计算结果显示:计算得到的电站进水口处涌浪高度与实测数据较为接近;色玉滑坡从失稳运动至静止堆积的持续时间约为20 s,颗粒平均速度最大达到16.12 m/s;滑坡引起的涌浪约在滑坡失稳10 s后传播到对岸,之后开始沿坡面向上爬升,最大爬升高度达到27.32 m。研究表明CFD–DEM流固耦合模型能够很好地应用于模拟山区河谷大规模滑坡涌浪灾害,可为库区防灾减灾提供高效的技术支持。

CFD study of non-premixed swirling burners: Effect of turbulence models

This research investigates a numerical simulation of swirling turbulent non-premixed combustion.The effects on the combustion characteristics are examined with three turbulence models:namely as the Reynolds stress model,spectral turbulence analysis and Re-Normalization Group.In addition,the P-1 and discrete ordinate(DO)models are used to simulate the radiative heat transfer in this model.The governing equations associated with the required boundary conditions are solved using the numerical model.The accuracy of this model is validated with the published experimental data and the comparison elucidates that there is a reasonable agreement between the obtained values from this model and the corresponding experimental quantities.Among different models proposed in this research,the Reynolds stress model with the Probability Density Function(PDF)approach is more accurate(nearly up to 50%)than other turbulent models for a swirling flow field.Regarding the effect of radiative heat transfer model,it is observed that the discrete ordinate model is more precise than the P-1 model in anticipating the experimental behavior.This model is able to simulate the subcritical nature of the isothermal flow as well as the size and shape of the internal recirculation induced by the swirl due to combustion.

Process Modeling of Ferrofluids Flow for Magnetic Targeting Drug Delivery

Among the proposed techniques for delivering drugs to specific sites within the human body, magnetic targeting drug delivery surpasses due to its non-invasive character and its high targeting efficiency. Although there have been some analyses theoretically for magnetic drug targeting, very few researchers have addressed the hydrodynamic models of magnetic fluids in the blood vessel of human body. This paper presents a mathematical model to describe the hydrodynamics of ferrofluids as drug carriers flowing in a blood vessel under the applied magnetic field. A 3D flow field of magnetic particles in a blood vessel model is numerically simulated in order to further understand clinical application of magnetic targeting drug delivery. Simulation results show that magnetic nanoparticles can be enriched in a target region depending on the applied magnetic field intensity. Magnetic resonance imaging confirms the enrichment of ferrofluids in a desired body tissue of Sprague-Dawley rats. The simulation results coincide with those animal experiments. Results of the analysis provide the important information and can suggest strategies for improving delivery in favor of the clinical application.

基于GA-BPNN代理模型的混合式黏滞阻尼器构造优化

采取CFD(computational fluid dynamics)数值模拟和基于代理模型的优化方法,研究混合式黏滞阻尼器在多参数设计空间内的构造参数优化问题。首先,分析黏滞阻尼器参数对力学性能的影响规律,基于正交试验理论选取间隙宽度、缸体内径、活塞厚度、阻尼孔直径为关键参数,利用优化拉丁超立方设计和CFD数值模拟获得初始样本点耗能性能指标;然后,使用遗传算法(genetic algorithm,GA)和反向传播神经网络(backpropagation neural network,BPNN)的方法构建代理模型,其能够准确反映构造参数耗能性能指标和构造参数之间的繁复关系。进一步地,循环更新GA-BPNN代理模型并结合非支配排序遗传算法(non-dominated sorting genetic algorithm-II,NSGA-II),以最佳耗能能力为目标,实现在全设计空间内的寻优,确定在典型阻尼介质黏度下双出杆混合式黏滞阻尼器的最优构造参数。最后,探讨了构造参数对黏滞阻尼器流动性能的影响机理。研究结果表明,优化双出杆混合式黏滞阻尼器构造参数在选用基于GA-BPNN代理模型的优化方法时,可有效提高计算效率且具有较高预测精度。从性能指标提升角度,全黏度下最优构造参数阻尼孔直径、活塞厚度、缸体内径和间隙宽度分别为1.31 mm、120.78 mm、199.87 mm、0.5 mm,相较于基准构造,最大阻尼力和能量耗材比分别提升33.8%和64.8%。该方法可为黏滞阻尼器构造参数优化及相关研究提供参考。

独头巷道射流通风流场CFD模拟研究

独头巷道压入式通风是有限空间的受限贴附射流。独头巷道通风风流流场是通风理论和通风设计的基础。笔者根据流体动力学和射流理论 ,建立了独头巷道压入式受限贴附射流通风的紊流k -ε数学模型 ,分析了计算边界条件 ,并应用计算流体动力学 (CFD)的方法模拟了独头巷道射流通风流场 ,从理论上得出了独头巷道有限空间受限贴附射流通风的规律 ,为研究独头巷道合理并有效通风提供了新的理论依据。

重气泄漏扩散实验的计算流体力学(CFD)模拟验证

运用CFD软件Fluent中的标准双方程湍流模型,对重气瞬时和连续泄漏的扩散进行了模拟以预测重气扩散过程中参数的变化,结果表明重气在垂直高度上的浓度随高度增加而减小,对于重气到达一点处的时间而言,瞬时泄漏的预测时间小于实际到达时间,而且浓度减小到零的时间也要先于实际的时间,连续泄漏的情形则相反,模拟过程假设风速和风向不变导致模拟结果没有实际的波动大。通过将模拟的最大摩尔浓度进行误差统计计算表明:Fluent对于连续泄漏源的扩散模拟结果最为准确。CFD模型能准确预测重气扩散过程中气体浓度的变化,可以应用于实际的风险分析和安全评价中。

CFD软件在对旋式轴流风机数值模拟中的应用

综合分析介绍了CFD软件在叶轮机械数值模拟中的两个关键问题,即数值算法和湍流模型及其最近的一些研究进展,并以对旋式轴流风机的数值模拟为例对其应用进行了举例说明,最后对CFD在叶轮机械数值模拟中的应用及发展趋势进行了展望。

基于CFD的高炉气场建模与仿真研究

高炉内部的变化过程较为复杂,高炉内固、液、气三相之间的动量、能量和质量传输存在着不可约束的关系,造成气场的随机性变化,传统的计算流体动力学的高炉建模是利用数学方程和计算机数值计算来仿真高炉气场的实际运行过程,没有充分考虑上述复杂变化造成的影响,造成气场测量结果不准。在充分研究传统方法基础上,采用列偏微分方程描述高炉内固、液、气三相之间的动量、能盘和质量,充分考虑高炉内的物理化学反应并做了适当的简化。用有限体积法对高炉模型进行求解,采用求解压力耦合方程的半隐式方法进行流场的计算。仿真结果表明,建立的模型能够准确反映高炉气场变化过程,提高了测量结果的准确性。

基于CFD降尺度的复杂地形风场数值模拟研究

在计算机流体力学(Computational Fluid Dynamics,CFD)模式Fluent的基础之上修改传统的RANS湍流参数化方案,选用大涡模拟(Large Eddy Simulation,LES)的湍流方案,并引入温度层结的浮力模型,得到修改后的Fluent模式。使用中尺度预报模式WRF和WRF耦合修改前后的Fluent模式模拟江西鄱阳湖地区内吉山测风站处2010年12月至2011年3月4个月的风速、风向和2011年3月6日吉山站附近地形流场以及气温场的变化过程。结合观测资料的对比发现,WRF模式在耦合Fluent后,对吉山单站点风速风向的模拟效果得到改善。WRF耦合Fluent的模拟方法在Fluent修改后(算例2),相比修改前(算例1)可以更精确地模拟吉山站各高度处的风速风向。4个月70 m高度平均风速WRF、算例1和算例2的平均误差分别为3. 963,2. 727和2. 224 m·s^-1。算例2与观测的70 m高度风向玫瑰图匹配程度总体上比算例1更高。算例2还可以模拟出白天不稳定状态下的热浮力效应和空间分布不均匀且较大的湍动能,能模拟出夜间大气边界层的逆温现象,而算例1则不能。以上结果均表明在对Fluent模式修改后,WRF耦合Fluent的模拟方法对吉山站附近风场的模拟效果得到改善。

Assessment of Turbulence Models on Bridge-Pier Scour Using Flow-3D

The main purpose of this paper is to analyze the influence of different turbulence flow models on scouring pit of bridge-pier. Flow-3D software is applied in line with the purpose. The key motivation for this study is to contribute to the Flow-3D software by means of some modification and adjustment in the sediment scour model and shallow water model. An assessment of turbulence model adopted with the parameters of the Melville experiment to estimate the maximum scour-depth was performed. In the simulation results, the alternate eddy formation and shedding were repeated while the Karman vortex street formed behind the pier for the large eddy simulation LES turbulence model is more realistic in the flow phenomenon. The results of the scour development of large eddy simulation (LES) turbulence model were found to be more satisfied than the Renormalized group (RNG) turbulence model and close to the prior experiment results. The simulated scour results were significantly different with the observed data collected from previous literature in the reason of some unsuitability of meshing method in Flow-3D software.

Modeling and simulation of chemically reacting flows in gas-solid catalytic and non-catalytic processes

This paper gives an overview of the recent development of modeling and simulation of chemically react- ing flows in gas-solid catalytic and non-catalytic processes. General methodology has been focused on the Eulerian-Lagrangian description of particulate flows, where the particles behave as the catalysts or the reactant materials. For the strong interaction between the transport phenomena （i.e., momentum, heat and mass transfer） and the chemical reactions at the particle scale, a cross-scale modeling approach, i.e., CFD-DEM or CFD-DPM, is established for describing a wide variety of complex reacting flows in multiphase reactors, Representative processes, including fluid catalytic cracking （FCC）, catalytic conversion of syngas to methane, and coal pyrolysis to acetylene in thermal plasma, are chosen as case studies to demonstrate the unique advantages of the theoretical scheme based on the integrated particle-scale information with clear physical meanings, This type of modeling approach provides a solid basis for understanding the multiphase reacting flow problems in general.

基于大涡模拟的NACA0012翼型流动分离研究

本文针对翼型流动分离问题,利用求解RANS方程和大涡模拟数值计算方法,通过常用的三种湍流模型的对比:k-epsilon、SST k-omega和BSL Reynolds Stress,最终选取SST k-omega湍流模型对NACA0012翼型进行定常流动和非定常流动数值计算,得到翼型的升力系数特性曲线和翼型上下翼面的速度和压力云图。研究结果表明,大涡模拟能够捕捉流动分离区域中主要涡结构,在一个周期的不同时间步能够观测到分离涡从附着、发展、脱落到再附着的完整演化过程,对翼型流动控制的研究具有一定的参考,为飞行器的增升减阻设计提供了理论支持。

跨介巡航器水下运动数学建模

跨介巡航器由于其巨大的应用潜力受到了广泛关注。对于几何结构复杂的跨介巡航器,目前还没有被广泛接受的建模方法。本研究提出了一种多手段结合的建模方法,建立了“同济飞鱼”水空两栖巡航器的完整数学模型。建模过程包含动力学和运动学的机理模型推导,以及模型参数的确定。在参数确定过程中,综合运用了基于计算流体力学的水动力仿真手段以及针对机械结构的实验辨识方法,从而获得了完整的数学模型。

气固流化床化学反应数值模拟中颗粒尺度模型研究进展

气固流化床由于其优良的气固接触效率和传热传质效率,已经被广泛应用于能源、矿冶、化工、制药等工业领域。本文针对颗粒流态化-反应系统数值模拟研究进行了综述,阐述了数值模拟的三个尺度:化学反应工程模型、双流体模型以及颗粒尺度模型。然后聚焦于基于CFD-DEM方法的变粒径颗粒流态化-化学反应过程模拟,梳理分析了6种颗粒反应模型,即均匀转化模型、缩粒反应模型、缩核反应模型、联合收缩模型、细颗粒反应模型和随机孔隙模型,并从颗粒性质变化、化学反应模型、不同尺度耦合三个角度探讨了不同的颗粒反应模型的优点和应用中的局限性,分析了跨尺度颗粒系统模拟方法的发展近况,最后讨论了CFD-DEM方法在气固流化床化学反应过程模拟的应用上未来可能的发展方向,包括颗粒尺度大规模高效计算算法、颗粒反应模型的精确化以及颗粒-气体信息传递的精细化描述方面。有助于气固流化床化学反应模拟领域的梳理和发展,尤其是可供颗粒尺度模拟领域的研究人员参考和借鉴。

不同运动状态下慢性阻塞性肺疾病患者下呼吸道内的气流特性

目的运用计算流体动力学方法探究不同运动状态下慢性阻塞性肺疾病(chronic obstructive pulmonary disease,COPD)患者下呼吸道内气流特性。方法收集稳定期COPD患者肺部CT扫描数据与肺功能数据,重建下呼吸道三维模型,通过施加个体化边界条件进行数值模拟,分析患者下呼吸道壁面压力、壁面剪切应力(wall shear stress,WSS)、气流速度以及压降等参数。结果随着运动强度增加,COPD患者下呼吸道壁面压力、WSS、流速及压降呈逐渐上升趋势。静息状态与低强度运动状态各参数相差较小,高强度运动状态各参数显著增加。其中,WSS是一个较敏感的力学指标,3种运动状态下WSS>1.0 Pa所占面积分别为272.35、438.24、4369.48 mm^(2)。结论运动状态下,COPD患者气道壁面压力、WSS、流速以及压降显著增加,增大患者气道黏膜损伤以及炎症的可能性。研究结果从力学角度解释COPD患者发生支气管炎症机制以及患者无法长时间运动的原因。

Ship maneuvering prediction based on virtual captive model test and system dynamics approaches

The maneuvering simulation is carried out through the continuous captive model test and the system dynamics approach.The mathematical maneuvering group(MMG)model is implemented in the virtual captive model tests by using the computational fluid dynamics(CFD)techniques.The oblique towing test(OTT),the circular motion test(CMT),the rudder force test and the open water test are performed to obtain the hydrodynamic derivatives of the hull,the rudder and the propeller,and the results are validated by experimental data.By designing the tests,the number of cases is reduced to a low level,to allow us to evaluate the maneuverability with a low cost and in a short time.Using these obtained coefficients,the system-based maneuvering simulations are conducted to calculate the position and the attitude of the ship,with results in agreement with the free running test results.This procedure can also be used for other hull forms,with reduced workload and with convenience for maneuvering simulation tasks.

混流式水轮机三维空化湍流场混合数值模拟

基于欧拉–欧拉方法中均匀多相流假设的混合两相流体无滑移模型,加入考虑气穴影响的Schnerr and Sauer空化模型,采用标准k-ε湍流模型和压力速度耦合的SIMPLEC算法,转动区域应用多重参考系模型,对某混流式水轮机全流道进行了三维定常空化湍流数值模拟。利用ANSYSFLUENT,获得了该水轮机在偏工况下转轮叶道和尾水管内空泡相的主要流动特征,分析了水轮机流道内空化发生的部位与程度。计算结果表明与单相流体模型相比该方法能有效地预测水轮机内的三维空化湍流场,可以较好地模拟水轮机内真实的有空化发生的多相流动情况。

汽车空调出风管道气动噪声分析与控制

通过耦合CFD(Computational Fluid Dynamics)与专业声学代码SYSNOISE求解汽车空调管道气动噪声,即利用LES(Large Eddy Simulation)湍流模型对空调管道的瞬态流场进行求解获得噪声源项,然后将噪声源项作为边界条件导入SYSNOISE来计算噪声的传播.根据流场分析与声场分析结果对空调管道的结构提出了两种改型方案,并对改型前后的空调系统噪声进行了测试.测试结果表明相比原始空调系统,两种方案都能有效降低噪声且方案二效果更好,驾驶员附近的噪声最大降幅达4.5 dB.