矩形斜板湿法除尘塔气液两相流数值模拟

以自主研制的矩形斜板湿法除尘塔为物理模型,采用CFD(计算流体力学)软件Fluent对塔内三维气液两相的流场进行了数值模拟.计算中气相采用标准k-ε湍流模型,液相采用拉格朗日离散相模型,液滴的壁面行为采用壁面液膜模型.结果表明:矩形斜板除尘塔能有效地增大气液接触面积,增强气液扰动,延长气体在塔内的停留时间;在塔体的进口区域会出现烟气冲壁和液滴冲壁的现象;在进气管一侧的塔体顶部会出现流动死区;喷淋液体对气场有一定的整流作用,在喷嘴处可以观察到气体卷吸的现象;增大进口烟速,可增大液滴在塔内的充满度,但同时会出现液滴夹带的现象.最后,在不同气速,不同的液气比下对塔内的压力损失进行了实验验证,实验值与模拟值吻合较好.

轴流压气机叶片表面盐雾颗粒沉积仿真

为研究轴流压气机在运行过程中盐雾颗粒在叶片表面的碰撞点和碰撞量分布,基于拉格朗日离散相(DPM)模型对不同旋转速度、不同盐雾粒径条件下压气机叶片表面盐雾颗粒碰撞状态进行了仿真,获取了压气机叶片表面盐雾颗粒碰撞分布规律;基于压气机轴对称结构开发了叶片表面盐雾碰撞位置及碰撞量的统计软件,对叶片表面盐雾颗粒碰撞情况进行了统计。结果表明:盐雾碰撞位置受压气机通道形状与盐雾颗粒受力大小影响,盐雾颗粒与叶片的碰撞主要发生在叶盆面,叶背面只有少量的盐雾颗粒能够到达;盐雾颗粒在叶片表面沉积的覆盖面积与盐雾颗粒直径呈正相关,在最大状态下且盐雾颗粒直径为5μm时,转子和静子叶盆表面盐雾颗粒沉积的覆盖面积分别为59.3%和55.3%;盐雾颗粒在叶片表面沉积的覆盖面积与压气机转速呈正相关,在慢车状态下且盐雾颗粒直径为5μm时,转子和静子叶盆表面盐雾颗粒沉积的覆盖面积分别为57%和42.9%。

豪华邮轮防疫区气流组织优化

新冠肺炎疫情爆发以来,对邮轮行业造成严重的影响。邮轮作为海上的人员密集场所,爆发疫情会更加严重,为了避免邮轮上出现在公共卫生、船舶防疫安全方面问题,文中对豪华邮轮防疫区的气流组织进行优化设计,通过CFD的方法对豪华邮轮防疫区的气流组织进行分析,运用数值模拟软件STAR CCM+对邮轮防疫区模型进行网格划分,采用拉格朗日多相流理论对病毒飞沫的运动情况进行模拟,设置初始条件和边界条件后进行模拟计算,根据病毒排除率对室内流场进行评价,为验证模型的准确性,将病毒飞沫运动模拟结果与实验数据进行对比,与实验结果保持一致,结果表明,送风角度和换气次数是影响病毒排出率的因素,改变送风角度和换气次数以提高邮轮防疫区的病毒排出率,找出邮轮防疫效果最优的通风设计方案,避免离岸疫情事件的发生。

LARGE-EDDY SIMULATION OF TWO-PHASE REACTING FLOW IN MODEL COMBUSTOR

The gas-droplet two-phase reacting flow in a model combustor with the V-gutter flame holder is studied by an Eulerian-Lagrangian large-eddy simulation (LES) approach. The k-equation subgrid-scale model is used to simulate the subgrid eddy viscosity, and the eddy-break-up (EBU) combustion subgrid-scale model is used to determine the chemical reaction rate. A two-step turbulent combustion subgrid-scale model is employed for calculating carbon monoxide CO concentration, and the NO subgrid-scale pollutant formation model for the evaluation of the rate of NO formation. The heat flux model is applied to the prediction of radiant heat transfer. The gas phase is solved with the SIMPLE algorithm and a hybrid scheme in the staggered grid system. The liquid phase equations are solved in a Lagrangian frame in reference of the particle-source-in-cell (PSIC) algorithm. From simulation results, the exchange of mass, moment and energy between gas and particle fields for the reacting flow in the afterburner with a V-gutter flame holder can be obtained. By the comparison of experimental and simulation results, profile temperature and pollutant of the outlet are quite in agreement with experimental data. Results show that the LES approach for predicting the two-phase instantaneous reacting flow and pollutant emissions in the afterburner is feasible.

Multi-phase signal setting and capacity of signalized intersection

A capacity model of multi-phase signalized intersections is derived by a stopping-line method. It is simplified with two normal situations： one situation involves one straight lane and one left-turn lane; the other situation involves two straight lanes and one left-turn lane. The results show that the capacity is mainly relative to signal cycle length, phase length, intersection layout and following time. With regard to the vehicles arrival rates, the optimal model is derived based on each phase＇s remaining time balance, and it is solved by Lagrange multipliers. Therefore, the calculation models of the optimal signal cycle length and phase lengths are derived and simplified. Compared to the existing models, the proposed model is more convenient and practical. Finally, a practical intersection is chosen and its signal cycles and phase lengths are calculated by the proposed model.

气动喷射数值仿真分析

利用CFD软件Fluent建立数学物理模型,运用欧拉法和拉格朗日方法相结合的计算模型对离散相模型(DPM)进行三维数值模拟。研究当进口处空气速度为60m/s时,不同直径的固体颗粒在喷管外部流场的轨迹和横截面上的分布。仿真得到以下结论:在固体颗粒从喷管喷出后短距离内,固体颗粒大体上呈现圆锥状喷射,喷射的锥角随颗粒的减小而逐步减小;颗粒直径减小时,长轴半径接近短轴半径,逐步过渡为圆形。

3D Multiphase Piecewise Constant Level Set Method Based on Graph Cut Minimization

Segmentation of three-dimensional(3D) complicated structures is of great importance for many real applications.In this work we combine graph cut minimization method with a variant of the level set idea for 3D segmentation based on the Mumford-Shah model.Compared with the traditional approach for solving the Euler-Lagrange equation we do not need to solve any partial differential equations.Instead,the minimum cut on a special designed graph need to be computed.The method is tested on data with complicated structures.It is rather stable with respect to initial value and the algorithm is nearly parameter free.Experiments show that it can solve large problems much faster than traditional approaches.

Gravitational Gauge Interactions of Dirac Field

Gravitational interactions of Dirac field are studied in this paper. Based on gauge principle, quantum gauge theory of gravity, which is perturbatively renormalizable, is formulated in the Minkowski space-time. In quantum gauge theory of gravity, gravity is treated as a kind of fundamental interactions, which is transmitted by gravitational gauge field, and Dirac field couples to gravitational field through gravitational gauge covariant derivative. Based on this theory, we can easily explain gravitational phase effect, which has already been detected by COW experiment.

Dynamic Adaptive Finite Element Analysis of Acoustic Wave Propagation Due to Underwater Explosion for Fluid-structure Interaction Problems

In this paper, an investigation into the propagation of far field explosion waves in water and their effects on nearby structures are carried out. For the far field structure, the motion of the fluid surrounding the structure may be assumed small, allowing linearization of the governing fluid equations. A complete analysis of the problem must involve simultaneous solution of the dynamic response of the structure and the propagation of explosion wave in the surrounding fluid. In this study, a dynamic adaptive finite element procedure is proposed. Its application to the solution of a 2D fluid-structure interaction is investigated in the time domain. The research includes：a） calculation of the far-field scatter wave due to underwater explosion including solution of the time-depended acoustic wave equation, b） fluid-structure interaction analysis using coupled Euler-Lagrangian approach, and c） adaptive finite element procedures employing error estimates, and re-meshing. The temporal mesh adaptation is achieved by local regeneration of the grid using a time-dependent error indicator based on curvature of pressure function. As a result, the overall response is better predicted by a moving mesh than an equivalent uniform mesh. In addition, the cost of computation for large problems is reduced while the accuracy is improved.

Gradient Transformation of Momentum and Single-Valued Vector Potential in Nonrelativistic Dynamics

A vector potential of a magnetic field in Lagrangian is defined as the necessary partial solution of a inhomogeneous differential equation. The ＂gradient transformation＂ is an addition of arbitrary general solution of the corresponding homogeneous equation that does not change the Lagrange equations. When dynamics is described by momenta and coordinates, this transformation is not the vector potential modification, which does not change expressions for other physical quantities, but a canonical transformation of momentum, which changes expressions for all fimctions of momentum, not changing the Poisson brackets, and, hence, the integrals of motion. The generating function of this transformation must reverse sign under the time-charge reversal. In quantum mechanics the unitary transformation corresponds to this canonical transformation. It also does not change the commutation relations. The phase of this unitary operator also must reverse sign under the time-charge reversal. Examples of necessary vector potentials for some magnetic fields are presented.

六流T型中间包夹杂物去除行为的数值模拟

以41 t圆坯连铸中间包为研究对象,运用ANSYS软件,结合流动模型、拉格朗日离散相模型模拟钢液流动和夹杂物行为。通过用户自定义函数为中间包钢渣界面的边界条件设置了一种新的判定标准,即根据夹杂物的受力情况判定夹杂物上浮去除或进入钢液。通过数值模拟计算中间包出口处夹杂物数密度,并与工业试验结果对比,发现新的判定标准较传统的捕捉(trap)边界条件具有更高的计算精度。基于上述模型计算了稳态浇铸过程中间包内不同粒径氧化铝夹杂物的上浮时间、上浮位置及去除率。上述结果为更好地研究中间包内夹杂物行为提供了支撑。

Inflation in Non-de Sitter Background with Coherent States

We use the excited coherent states built over the initial non-de Sitter modes,to study the modification of spectra of primordial scalar fluctuation.Non-de Sitter modes are actually the asymptotic solution of the inflaton field equation[J.High Energy Phys.09（2014） 020].We build excited coherent states over the non-de Sitter modes and despite the Jack of interactions in the Lagrangian,we find a non-zero one-point function.It is shown that the primordial non-Gaussianity resulting from excited-de Sitter modes depend both of time and background space-time.It is very tiny of order（≤10^-24）,at the Planck initial fixed time that confirmed by resent observations for single field inflation but it grows in the present epoch.Moreover,our results at the leading order are similar to what obtained with general initial states and in the dS limit leads to standard results[J.Cosmol.Astropart.Phys.1202（2012） 005].We will show that the non-dS modes and its resulting spectrum are more usable for far past time limit.

Lagrangian coherent structures analysis of gas-liquid flow in a bubble column

The objective of this paper is to apply a new identifying method to investigating the gas-liquid two-phase flow behaviors in a bubble column with air injected into water. In the numerical simulations, the standard k-c turbulence model is employed to de- scribe the turbulence phenomenon occurring in the continuous fluid. The Finite-Time Lyapunov Exponent （FTLE） and Lagrangian Coherent Structures （LCS） are applied to analyze the vortex structures in multiphase flow. Reasonable agreements are obtained between the numerical and experimental data. The numerical results show that the evolution of gas-liquid in the column includes initial and periodical developing stages. During the initial stage, the bubble hose is forming and extending along the vertical direction with the vortex structures formed symmetrically. During the periodical developing stage, the bub- ble hose starts to oscillate periodically, and the vortexes move along the bubble hose to the bottom of column alternately. Compared to the Euler-system-based identification criterion of a vortex, the FTLE field presents the boundary of a vortex without any threshold defined and the LCS represents the divergence extent of infinite neighboring particles. During the initial stage, the interfaces between the forward and backward flows are highlighted by the LCS. As for the periodical developing stage, the LCS curls near the vortex centers, providing a method of analyzing a flow field from a dynamical system perspec- tive.

Similarity between the Spiral Arms of Galaxy M51 Image and the Interface Curve of Yin-Yang Balance in the Ancient Tai-Chi Diagram

The particle paths of the Lagrangian flow field between two cylinders simulate well the spiral arms of Galaxy M51 image [1] and the interface curve of the Yin-Yang balance in the ancient Tai-Cbi diagram [2]. The particle paths of the Lagrangian flow field involve four parameters. The normalization of the system of equations significantly simplifies the formulation of the flow process and reduces the original four parameters to only one parameter. Furthermore it provides the similarity between the formulation of the spiral arms of Galaxy M51 and that of the interface curve of the Yin-Yang balance in the ancient Tai-Chi diagram.

The Role of α1(1260) in π^-p→α1^-(1260)p and π^-p → π^-ρ^0p Reactions Near Threshold

We report on a theoretical study of the π^-→α1（1260）p and π^-→π^-~0p reactions near threshold within an effective Lagrangian approach.The production process is described by t-channel ρ^0 meson exchange.For the π^-→π^-ρ~0p reaction,the final π^-p^0 results from the decay of the α1（1260） resonance,which is assumed as a dynamically generated state from the K＊ K and ρπ coupled channel interactions.We calculate the total cross section of the π^-→α1（1260）p reaction.It is shown that,with the coupling constant of the α1（1260） to ρπ channel obtained from the chiral unitary theory and a cut off parameter Δρ～1.5 GeV in the form factors,the experimental measurement can be reproduced.Furthermore,the total and differential cross sections of π^p→α1（1260）p→π^ρ^0p reaction are evaluated,and it is expected that our model calculations can be tested by future experiments.These reactions are important for the study of the α1（1260） resonance and would provide further constraints on the properties of the α1（1260） state.