High-order targeted essentially non-oscillatory scheme for two-fluid plasma model

The weakly ionized plasma flows in aerospace are commonly simulated by the single-fluid model,which cannot describe certain nonequilibrium phenomena by finite collisions of particles,decreasing the fidelity of the solution.Based on an alternative formulation of the targeted essentially non-oscillatory(TENO)scheme,a novel high-order numerical scheme is proposed to simulate the two-fluid plasmas problems.The numerical flux is constructed by the TENO interpolation of the solution and its derivatives,instead of being reconstructed from the physical flux.The present scheme is used to solve the two sets of Euler equations coupled with Maxwell's equations.The numerical methods are verified by several classical plasma problems.The results show that compared with the original TENO scheme,the present scheme can suppress the non-physical oscillations and reduce the numerical dissipation.

Temperature and current sensitivity extraction of optical superconducting transition-edge sensors based on a two-fluid model

Optical superconducting transition-edge sensor(TES)has been widely used in quantum information,biological imaging,and fluorescence microscopy owing to its high quantum efficiency,low dark count,and photon number resolving capability.The temperature sensitivity(α_(I))and current sensitivity(β_(I))are important parameters for optical TESs,which are generally extracted from the complex impedance.Here we present a method to extractα_(I)andβ_(I)based on a two-fluid model and compare the calculated current-voltage curves,pulse response,and theoretical energy resolution with the measured ones.This method shows qualitative agreement that is suitable for further optimization of optical TESs.

Anisotropic Plane Symmetric Two-Fluid Cosmological Model with Time-Varying G and A

We investigate a two-fluid anisotropic plane symmetric cosmological model with variable gravitational constant G（t） and cosmological term A（t）. In the two-fluid model, one fluid is chosen to be that of the radiation field modeling the cosmic microwave background and the other one a perfect fluid modeling the material content of the universe. Exact solutions of the field equations are obtained by using a special form for the average scale factor which corresponds to a specific time-varying deceleration parameter. The model obtained presents a cosmological scenario which describes an early acceleration and late-time deceleration. The gravitation constant increases with the cosmic time whereas the cosmological term decreases and asymptotically tends to zero. The physical and kinematical behaviors of the associated fluid parameters are discussed.

REVIEW ON MATHEMATICAL ANALYSIS OF SOME TWO-PHASE FLOW MODELS

The two-phase flow models are commonly used in industrial applications, such as nuclear, power, chemical-process, oil-and-gas, cryogenics, bio-medical, micro-technology and so on. This is a survey paper on the study of compressible nonconservative two-fluid model, drift-flux model and viscous liquid-gas two-phase flow model. We give the research developments of these three two-phase flow models, respectively. In the last part, we give some open problems about the above models.

Experimental Determination and Modeling of Bubble Size Distributions in Bubble Columns

Using a five point conductivity technique local values of bubble size,bubble velocity and gas fractionhave been experimentally determined in a 288 mmID and 4.3 m high bubble column as a function of axial andradial position for the air/water and CO2/N2/aqueous MDEA systems.The experimental results are comparedwith predictions from a fundamental two-fluid model.The implementation of a non-steady lateral drag term inthe two-fluid model has been shown.In addition to improving the physical realism of the model,it is found togive slight improvements in the predictions of the distributions of local bubble size.Predictions of bubble size arefound in reasonable agreement with experimental values in the heterogeous flow regime,whereas they are stil1found to be unreliable at low gas velocities.Local void predictions are found in reasonable agreement with experi-mental values,but deviations occur in the homogeneous flow regime towards the wall.This is attributed to defi-ciencies in the simplified bubble size

A THREE-FLUID MODEL OF THE SAND-DRIVEN FLOW

The sand-driven flow is studied from the continuum viewpoint in this paper. The crux of this work is how to model the stresses of the particle phase properly. By analysing the two-fluid model which usually, works in solving gas-particle two-phase .flow,. we find that this model has many. deficiencies for studying the sand-driven flow,even for the simplest case- the steady, two-dimensional fully-developed flow.Considering this, we have proposed the three-fluid model in which the upward particles and the downward-particles ore regarded as two kinds of fluids respectively.It is shown that the three-fluid model is better than the two-fluid model in reflecting the internal structure of the flow, region and the influence of the boundary situations on the flow. and it is advantageous to find an approximate solution in that the main components of the particle-phase stresses can be explicitly expressed by those variables in the three-fluid model.In the end, the governing equations as well as the boundary. conditions for the three-fluid model are provided with a discussion.

An improved semi-empirical friction model for gas-liquid two-phase flow in horizontal and near horizontal pipes

Pressure drop and liquid hold-up are two very important fluid flow parameters in design and control of multiphase flow pipelines.Friction factors play an important role in the accurate calculation of pressure drop.Various empirical and semi-empirical closure relations exist in the literature to calculate the liquid-wall,gas-wall and interfacial friction in two-phase pipe flow.However most of them are empirical correlations found under special experimental conditions.In this paper by modification of a friction model available in the literature,an improved semiempirical model is proposed.The proposed model is incorporated in the two-fluid correlations under equilibrium conditions and solved.Pressure gradient and velocity profiles are validated against experimental data.Using the improved model,the pressure gradient deviation from experiments diminishes by about 3%;the no-slip condition at the interface is satisfied and the velocity profile is predicted in better agreement with the experimental data.

Prediction of pressure gradient and hold-up in horizontal liquid-liquid pipe flow

This paper aims to propose correlations to predict pressure gradient,friction factor and fluid phase hold-up in liquid-liquid horizontal pipe flow.To develop the correlations,experiments are conducted using high viscous oils(202 and 630 mPa⋅s)in a steel pipe of length 11.25 m and length-to-diameter ratio of 708.In addition,the experimental data from the literature comprising wide range of flow and fluid properties is analyzed.For the analysis,the liquid-liquid pipe flow data is categorized into two as:stratified and dispersed.The existing friction factor correlations are modified to incorporate the effects of viscosity of the oil phase,interfacial curvature(contact/wetting angle-in lieu of material of the pipe)and fluid phase fraction.In the two-fluid model of stratified flow,the wall stress and interfacial stress correlations are substituted with superficial velocities of fluids and superficial Reynolds numbers of fluid phases replacing fluid phase velocities and fluid Reynolds numbers.Similarly,for dispersed flow,an effective Reynolds number is described as the sum of superficial Reynolds number of oil and water phases.Substituting the generally employed mean or mixture Reynolds number with the effective Reynolds number into the existing single-phase turbulent flow friction factor correlation,an effective friction factor for oil-water flow is proposed.Employing the proposed correlations,the pressure gradient across the oil-water flow and hold-up volume fraction are predicted with significant reduction in error compared with that of conventionally employed correlations.The average error and standard deviation values of−7.06%,20.72%and 0.31%,18.79%are found for stratified flow and dispersed flow respectively.

Validation of an improved two-fluid model with particle rotation for gas-solid fluidized bed

Gas-solid fluidized beds are widely applied in chemical and process engineering.It is of significance to establish a reasonable and effective mathematical model to explore the hydrodynamics of gas-particle system for industrial applications.As a less computationally demanding alternative to the discrete descriptions,two-fluid model considering kinetic theory of granular flow is often adopted to describe the fluidized behaviors of particles,but it cannot characterize the rotation of particles and its influence on the fluidized behaviors.In this study,to address the rotation effect of the fluidized particles,a two-fluid model combining the classical fluid and micropolar fluid is established,namely CMTFM.In the CMTFM,classical fluid is used to describe the motion of gas phase,while micropolar fluid is adopted to describe the motion of particle phase,and the rotation of particles and its influence on the hydrodynamics of the gas-particle system are characterized by the degree of freedom of microrotation and the improved drag force based on micropolar viscosities.In the calculation of the gas-solid bubbling fluidized bed,we investigated the influence of the microstructure parameters,particle-particle collision restitution coefficient and inlet velocity,and the results are compared to those from TFM model and experiments.Through the analysis,it manifests that pressure drop and expansion height of the fluidized bed under the consideration of the microrotation effect are closer to the experiments,which demonstrates the feasibility and advantage of the classical-micropolar two-fluid model.

陶瓷干法造粒过程坯料颗粒成形与雾化液含量的影响

为研究陶瓷干法造粒制粉过程坯料颗粒成形与雾化液含量的关系,基于欧拉-欧拉双流体模型模拟干法造粒制粉过程坯料颗粒与雾化液混合过程,同时对坯料颗粒流动性、颗粒级配及粗糙度进行实验分析,验证数值模拟结果正确性。仿真结果表明:当雾化液含量分别为100 m L、200 m L、300 m L时,坯料颗粒在造粒室内的分散性无明显差异,团聚现象不明显;当雾化液含量分别为400 m L、500 m L时,坯料颗粒在造粒室内的分散性有明显变化,团聚现象显著。实验结果表明:当雾化液含量分别为100 m L、200 m L、300 m L、400 m L、500 m L时,坯料颗粒的流动性指数依次为63.5%、83.0%、90.0%、77.0%、61.0%,有效坯料颗粒百分比依次为72%、83%、90%、82%、65%,粗糙度系数平均值依次为1.38、1.43、1.26、1.49、1.57。综合分析说明:数值仿真与实验结果基本相吻合,造粒过程中雾化液含量为300 m L时,干法造粒制粉过程造粒室内坯料颗粒的分散性较好,且基本无团聚现象;坯料颗粒的流动性最佳、颗粒级配最均匀、粗糙度整体最优,即造粒效果最好。

基于CFD的建筑陶瓷干法制粉造粒室倾斜率的分析

针对造粒室倾斜率对干法制粉造粒效果的影响。基于欧拉-欧拉双流体模型建立干法造粒数学模型,简化干法造粒装置建立物理模型,模拟不同造粒室倾斜率对造粒室内坯料颗粒的分布情况,优化造粒室倾斜率,结合实验分析坯料颗粒的流动性指数验证数值仿真的正确性。数值分析表明:当造粒室倾斜角分别为5°、15°、25°、35°、45°时,坯料颗粒在造粒室内的体积分布依次为1/3、2/5、1/2、1/2、1/2,造粒室内坯料颗粒的最大堆积度依次为0.6、0.45、0.42、0.42、0.6,且造粒室倾斜角为25°时坯料颗粒在造粒室内分布均匀性最好。实验分析表明:当造粒室倾斜角分别为5°、15°、25°、35°、45°时,坯料颗粒的流动性指数分别为61.11、78.45、93.06、88.23、72.11,造粒室倾斜角为25°时坯料颗粒的流动性最佳。综上分析可知:造粒室最佳倾斜角为25°,此时造粒室内坯料颗粒的体积分布最大,堆积密度最小,分布均匀性最好,且坯料颗粒的流动性最佳。

运动罐体内液体晃动的双向流固耦合数值分析

针对部分充液运动罐体内液体晃动对罐车运输安全的问题,以带有单个防波板的运动罐体模型为基础,采用双向流固耦合方法,对运动罐车在刹车过程中罐体内液体的晃动现象进行了数值分析,研究了不同材料防波板在载液罐体内的受力情况,以及在刹车制动过程中罐体内气液两相分布状态,从而获得了采用单向耦合方法不能获得的罐体结构应力随时间的变化历程.研究结果表明:罐体端面受力随着充液比的增加而增大,当充液比为0.8时,罐体的总体受力最大;对于不同材料的防波板,当防波板变形较小时,其对罐体端面和罐体整体受力的影响相对较小,防波板的最大剪切应力随着材料剪切模量的增大而非线性减小.

卧式搅拌釜气液两相流场的参数化研究

基于Fluent软件,采用SST k−ω湍流模型、欧拉−欧拉两相流模型和多重参考系法对卧式搅拌釜气液两相流场进行数值模拟,并采用示踪剂法研究釜内混合过程。结果表明:增大转速或气体流量有利于气相分布更均匀并加快液相的混合。当搅拌转速超过93 r/min时,相对功率消耗基本不变。上叶轮倾斜角的变化对气相分布的影响很小。当倾角为50°时,相对功率消耗最大。适当提高桨叶离底高度可以提高气含率并改善气相分布,但会增加液相混匀时间。

陶瓷墙地砖干法造粒过程坯料粉体成形与造粒室转速的影响

为分析陶瓷墙地砖干法造粒过程坯料粉体成形与造粒室转速的关系。基于欧拉-欧拉双流体模型模拟陶瓷干法造粒混料过程数理模型,同时对坯料粉体粗糙度、粉体级配及粉体流动性指数进行实验分析,验证数值模拟的正确性。当造粒室转速分别为120 RPM、140 RPM、160 RPM时,坯料粉体体积分布大小基本保持不变,坯料粉体均匀性和分散性逐渐变好,团聚现象逐渐消失;当造粒室转速分别为180 RPM、200 RPM时,坯料粉体体积分布大小仍基本保持不变,坯料粉体均匀性和分散性逐渐变差,团聚现象逐渐明显。实验结果表明:当造粒室转速分别为120 RPM、140 RPM、160 RPM、180 RPM、200 RPM时,坯料粉体粗糙度系数平均值依次为1.79、1.77、1.68、1.74、1.78;粉体级配百分比依次为73%、77%、89%、80%、72%;流动性指数依次为63.54、66.95、69.75、68.32、67.21。综合分析说明:造粒室转速为160 RPM时,坯料粉体均匀性和分散性良好,且无明显团聚现象,此时坯料粉体粗糙度系数平均值最小、粉体级配百分比最高、流动性指数最大,即造粒效果最好。

Two-fluid modeling of Geldart A particles in gas-fluidized beds

We have investigated the effect of cohesion and drag models on the bed hydrodynamics of Geldart A particles based on the two-fluid （TF） model. For a high gas velocity U0 = 0.03 m/s, we found a transition from the homogeneous fluidization to bubbling fluidization with an increase of the coefficient C1, which is used to account for the contribution of cohesion to the excess compressibility. Thus cohesion can play a role in the bed expansion of Geldart A particles. Apart from cohesion, we have also investigated the influence of the drag models. When using the Wen and Yu drag correlation with an exponent n = 4.65, we find an under-prediction of the bed expansion at low gas velocities （U0 = 0.009 m/s）. When using a larger exponent （n = 9.6）, as reported in experimental studies of gas-fluidization, a much better agreement with the experimental bed expansion is obtained. These findings suggest that at low gas velocity, a scale-down of the commonly used drag model is required. On the other hand, a scale-up of the commonly used drag model is necessary at high gas velocity （U0 = 0.2 and 0.06 m/s）. We therefore conclude that scaling the drag force represent only an ad hoc way of repairing the deficiencies of the TF model, and that a far more detailed study is required into the origin of the failure of the TF model for simulating fluidized beds of fine powders.

Two-fluid modeling of Geldart A particles in gas-solid micro-fluidized beds

The fiuidization behavior of Geldart A particles in a gas-solid micro-fluidized bed was investigated by Eulerian-Eulerian numerical simulation. The commonly used Gidaspow drag model was tested first. The simulation showed that the predicted minimum bubbling velocities were significantly lower than the experimental data even when an extremely fine grid size （of approximately one particle diameter） was used. The modified Gibilaro drag model was therefore tested next. The predicted minimum bubbling velocity and bed voidage were in reasonable agreement with the experimental data available in literature. The experimentally observed regime transition phenomena from bubbling to slugging were also reproduced successfully in the simulations. Parametric studies indicated that the solid-wall boundary conditions had a significant impact on the predicted gas and solid flow behavior.

Runout prediction and dynamic characteristic analysis of a potential submarine landslide in Liwan 3-1 gas field

A large number of submarine landslides with different scales have been identified in the canyon area of the submarine pipeline route of Liwan 3-1 gas field. There is still much chance that submarine slope failures would happen, and the following mass movement would present great risk to the submarine pipeline. In view of this, a numerical prediction method based on Eulerian-Eulerian two-phase flow model is introduced to simulate the mass movement of potential submarine landslides. The sliding soil and ambient water are respectively simulated by Herschel-Bulkley rheology model and Newtonian fluid model. The turbulence is simulated using the k-e model. Compared with both the experiment data and Bing result, the two-phase flow model shows a good accuracy, and its result is more close to the actual situation; the dynamic coupling between soil and ambient water can be effectively simulated and the phenomena of hydroplaning and head detachment can be obtained. Finally, the soil movement of a potential submarine landslide is simulated as an example, according to the seismic profile in the canyon area. The result shows that the hydroplaning occurs during the movement process. The runout distance calculated by the two-phase flow model is 877 m, which is 27.1% larger than the Bing result. However, the peak front velocity of soil is relative small, with a maximum value of 8.32 m/s. The Bing program with a simple and rapid process can be used for a preliminary evaluation, while the two-phase flow model is more appropriate for an accurate assessment.

Fluid Flow Behavior of Liquid in Cylindrical Vessels Stirred by One or Two Air Jets

Based on the two-phase model (Eulerian-Eulerian model), the three dimensional fluid flow in water and that liquid steel systems stirred by one or two multiple gas jets are simulated. In the Eulerian-Eulerian two-phase model, the gas and the liquid phase are considered to be two different continuous fluids interacting with each other through the finite inter-phase areas. The exchange between the phases is represented by source terms in conversation equations. Turbulence is assumed to be a property of the liquid phase. A new turbulence modification - model is introduced to consider the bubbles movement contribution to and . The dispersion of phases due to turbulence is represented by introducing a diffusion term in mass conservation equation. The mathematical simulation agrees well with the experiment results. The study results indicate that the distance of two nozzles has big effect on fluid flow behavior in the vessel. Using two gas injection nozzles at the half radii of one diameter of the bottom generates a much better mixing than with one nozzle under the condition of the same total gas flow rate.

Influence of core box vents distribution on flow dynamics of core shooting process based on experiment and numerical simulation

Core shooting process plays a decisive role in the quality of sand cores, and core box vents distribution is one of the most important factor determining the effectiveness of core shooting process. In this paper, the influence of core box vents distribution on the flow dynamics of core shooting process was investigated based on in situ experimental observations with transparent core box, high-speed camera and pressure measuring system. Attention was focused on the variation of both the flow behavior of sand and pressure curves due to different vents distribution. Taking both kinetic and frictional stress into account, a kinetic-frictional constitutive model was established to describe the internal momentum transfer in the solid phase. Two-fluid model(TFM) simulation was then performed and good agreement was achieved between the experimental and simulated results on both the flow behavior of sand and the pressure curves. It was found that vents distribution has direct effect on the pressure difference of different locations in the core box, which determines the buoyancy force exerting on the sand particles and significantly influences the filling process of core sand.

Numerical simulations of gas-particle flow behavior created by low-level rotary-winged aircraft flight over particle bed

The aerodynamics of gas-particle suspensions is simulated as an Euler-Euler two-fluid model in a revolving rotor over a particle bed. The interactions of collisions between the blade and particles and particle-particle interactions are modeled using the kinetic theory of granular flow(KTGF). The gas turbulence induced by the rotation of the rotor is modeled using the kg-εg model. The flow field of a revolving rotor is simulated using the multiple reference frame(MRF) method. The distributions of velocities, volume fractions, and gas pressure are predicted while the aircraft hovers at different altitudes.The gas pressure decreases from the hub to the tip of the blade, and it is higher at the pressure side than that at the suction side of the rotor. The turbulent kinetic energy of the gas increases toward the blade tip. The volume fraction of particles decreases as the hovering altitude increases. The simulated pressure coefficient is compared with that in experimental measurements.