Review:Recent Development of High⁃Order⁃Spectral Method Combined with Computational Fluid Dynamics Method for Wave⁃Structure Interactions

The present paper reviews the recent developments of a high⁃order⁃spectral method(HOS)and the combination with computational fluid dynamics(CFD)method for wave⁃structure interactions.As the numerical simulations of wave⁃structure interaction require efficiency and accuracy,as well as the ability in calculating in open sea states,the HOS method has its strength in both generating extreme waves in open seas and fast convergence in simulations,while computational fluid dynamics(CFD)method has its advantages in simulating violent wave⁃structure interactions.This paper provides the new thoughts for fast and accurate simulations,as well as the future work on innovations in fine fluid field of numerical simulations.

Analysis of Temperature Rise in High-Speed Permanent Magnet Synchronous Traction Motors by Coupling the Equivalent Thermal Circuit Method and Computational Fluid Dynamics

To solve the problem of temperature rise caused by the high power density of high-speed permanent magnet synchronous traction motors,the temperature rise of various components in the motor is analyzed by coupling the equivalent thermal circuit method and computational fluid dynamics.Also,a cooling strategy is proposed to solve the problem of temperature rise,which is expected to prolong the service life of these devices.First,the theoretical bases of the approaches used to study heat transfer and fluid mechanics are discussed,then the fluid flow for the considered motor is analyzed,and the equivalent thermal circuit method is introduced for the calculation of the temperature rise.Finally,the stator,rotor loss,motor temperature rise,and the proposed cooling method are also explored through experiments.According to the results,the stator temperature at 50,000 r/min and 60,000 r/min at no-load operation is 68℃ and 76℃,respectively.By monitoring the temperature of the air outlets inside and outside the motor at different speeds,it is also found that the motor reaches a stable temperature rise after 65 min of operation.Coupling of the thermal circuit method and computational fluid dynamics is a strategy that can provide the average temperature rise of each component and can also comprehensively calculate the temperature of each local point.We conclude that a hybrid cooling strategy based on axial air cooling of the inner air duct of the motor and water cooling of the stator can meet the design requirements for the ventilation and cooling of this type of motors.

Computational fluid dynamics-discrete element method simulation of stirred tank reactor for graphene production

Liquid phase exfoliation(LPE)process for graphene production is usually carried out in stirred tank reactor and the interactions between the solvent and the graphite particles are important as to improve the production efficiency.In this paper,these interactions were revealed by computational fluid dynamics–discrete element method(CFD-DEM)method.Based on simulation results,both liquid phase flow hydrodynamics and particle motion behavior have been analyzed,which gave the general information of the multiphase flow behavior inside the stirred tank reactor as to graphene production.By calculating the threshold at the beginning of graphite exfoliation process,the shear force from the slip velocity was determined as the active force.These results can support the optimization of the graphene production process.

Simulations of Compressible Two-Medium Flow by Runge-Kutta Discontinuous Galerkin Methods with the Ghost Fluid Method

The original ghost fluid method (GFM) developed in [13] and the modifiedGFM (MGFM) in [26] have provided a simple and yet flexible way to treat twomediumflow problems. The original GFM and MGFM make the material interface"invisible" during computations and the calculations are carried out as for a singlemedium such that its extension to multi-dimensions becomes fairly straightforward.The Runge-Kutta discontinuous Galerkin (RKDG) method for solving hyperbolic conservationlaws is a high order accurate finite element method employing the usefulfeatures from high resolution finite volume schemes, such as the exact or approximateRiemann solvers, TVD Runge-Kutta time discretizations, and limiters. In this paper,we investigate using RKDG finite element methods for two-medium flow simulationsin one and two dimensions in which the moving material interfaces is treated via nonconservativemethods based on the original GFM and MGFM. Numerical results forboth gas-gas and gas-water flows are provided to show the characteristic behaviors ofthese combinations.

Analysis of gas-solid flow and shaft-injected gas distribution in an oxygen blast furnace using a discrete element method and computational fluid dynamics coupled model

lronmaking using an oxygen blast furnace is an attractive approach for reducing energy consumption in the iron and steel industry. This paper presents a numerical study of gas-solid flow in an oxygen blast fur- nace by coupling the discrete element method with computational fluid dynamics. The model reliability was verified by previous experimental results. The influences of particle diameter, shaft tuyere size, and specific ratio （X） of shaft-injected gas （51G） flowrate to total gas flowrate on the SIC penetration behavior and pressure field in the furnace were investigated. The results showed that gas penetration capacity in the furnace gradually decreased as the particle diameter decreased from 100 to 40 mm. Decreasing particle diameter and increasing shaft tuyere size both slightly increased the SIG concentration near the furnace wall but decreased it at the furnace center. The value of X has a significant impact on the SIG distribution. According to the pressure fields obtained under different conditions, the key factor affecting SIG penetration depth is the pressure difference between the upper and lower levels of the shaft tuyere. If the pressure difference is small, the SIG can easily penetrate to the furnace center.

Computational fluid dynamics simulations of respiratory airflow in human nasal cavity and its characteristic dimension study

To study the airflow distribution in human nasal cavity during respiration and the characteristic parameters of nasal structure, three-dimensional, anatomically accurate representations of 30 adult nasal cavity models were recons- tructed based on processed tomography images collected from normal people. The airflow fields in nasal cavities were simulated by fluid dynamics with finite element software ANSYS. The results showed that the difference of human nasal cavity structure led to different airflow distribution in the nasal cavities and variation of the main airstream passing through the common nasal meatus. The nasal resistance in the regions of nasal valve and nasal vestibule accounted for more than half of the overall resistance. The characteristic model of nasal cavity was extracted on the basis of characteristic points and dimensions deduced from the original models. It showed that either the geometric structure or the airflow field of the two kinds of models was similar. The characteristic dimensions were the characteristic parameters of nasal cavity that could properly represent the original model in model studies on nasal cavity.

Numerical Study on the Aerodynamic and Fluid−Structure Interaction of An NREL-5MW Wind Turbine

A 5-MW wind turbine has been modeled and analyzed for fluid-structure interaction and aerodynamic performance.In this study, a full-scale model of a 5-MW wind turbine is first developed based on a computational fluid dynamics(CFD) approach, in which the unsteady, noncompressible Reynolds Averaged Navier-Stokes(RANS) method is used. The main focus of the study is to analyze the tower shadow effect on the aerodynamic performance of the wind turbine under different inlet flow conditions. Subsequently, the finite element model is established by considering fluid/structure interactions to study the structural stress, displacement, strain distributions and flow field information of the structure under the uniform wind speed. Finally, the fluid-structure interaction model is established by considering turbulent wind and the tower shadow effect. The variation rules of the dynamic response of the one-way and two-way fluid-structure interaction(FSI) models under different wind speeds are analyzed, and the numerical calculation results are compared with those of the centralized mass model. The results show that the tower shadow effect and structural deformation are the main factors affecting the aerodynamic load fluctuation of the wind turbine, which in turn affects the aerodynamic performance and structural stability of the blades. The structural dynamic response of the coupled model shows significant similarity, while the structural displacement response of the former exhibits less fluctuation compared with the conventional centralized mass model. The one-way fluid-structure interaction(FSI)model shows a higher frequency of stress-strain and displacement oscillations on the blade compared with the two-way FSI model.

Computational Fluid Dynamics(CFD) Analysis and Optimization of Reconstructed Intake System of Cylinder Head Based on Slicing Reverse Method

To find out and improve the flow characteristics inside the intake system of cylinder head,the application of computational fluid dynamics(CFD)in the evaluation and optimization of the reconstructed intake system based on slicing reverse method was proposed.The flow characteristics were found out through CFD,and the velocity vector field,pressure field and turbulent kinetic energy field for different valve lifts were discussed,which were in good agreement with experimental data,and the quality of reconstruction was evaluated.In order to improve its flow characteristic,an optimization plan was proposed.The results show that the flow characteristics after optimization are obviously improved.The results can provide a reference for the design and optimization of the intake system of cylinder head.

Numerical Solutions of the Classical and Modified Buckley-Leverett Equations Applied to Two-Phase Fluid Flow

Climate change is a reality. The burning of fossil fuels from oil, natural gas and coal is responsible for much of the pollution and the increase in the planet’s average temperature, which has raised discussions on the subject, given the emergencies related to climate. An energy transition to clean and renewable sources is necessary and urgent, but it will not be quick. In this sense, increasing the efficiency of oil extraction from existing sources is crucial, to avoid waste and the drilling of new wells. The purpose of this work was to add diffusive and dispersive terms to the Buckley-Leverett equation in order to incorporate extra phenomena in the temporal evolution between the water-oil and oil-water transitions in the pipeline. For this, the modified Buckley-Leverett equation was discretized via essentially weighted non-oscillatory schemes, coupled with a three-stage Runge-Kutta and a fourth-order centered finite difference methods. Then, computational simulations were performed and the results showed that new features emerge in the transitions, when compared to classical simulations. For instance, the dispersive term inhibits the diffusive term, adding oscillations, which indicates that the absorption of the fluid by the porous medium occurs in a non-homogeneous manner. Therefore, based on research such as this, decisions can be made regarding the replacement of the porous medium or the insertion of new components to delay the replacement.

NUMERICAL SIMULATION OF UNSTEADY-STATE UNDEREXPANDED JET USING DISCONTINUOUS GALERKIN FINITE ELEMENT METHOD

A discontinuous Galerkin finite element method （DG-FEM） is developed for solving the axisymmetric Euler equations based on two-dimensional conservation laws. The method is used to simulate the unsteady-state underexpanded axisymmetric jet. Several flow property distributions along the jet axis, including density, pres- sure and Mach number are obtained and the qualitative flowfield structures of interest are well captured using the proposed method, including shock waves, slipstreams, traveling vortex ring and multiple Mach disks. Two Mach disk locations agree well with computational and experimental measurement results. It indicates that the method is robust and efficient for solving the unsteady-state underexpanded axisymmetric jet.

CVBEM and FVM Computational Model Comparison for Solving Ideal Fluid Flow in a 90-Degree Bend

While finite volume methodologies (FVM) have predominated in fluid flow computations, many flow problems, including groundwater models, would benefit from the use of boundary methods, such as the Complex Variable Boundary Element Method (CVBEM). However, to date, there has been no reporting of a comparison of computational results between the FVM and the CVBEM in the assessment of flow field characteristics. In this work, the CVBEM is used to develop a flow field vector outcome of ideal fluid flow in a 90-degree bend which is then compared to the computational results from a finite volume model of the same situation. The focus of the modelling comparison in the current work is flow field trajectory vectors of the fluid flow, with respect to vector magnitude and direction. Such a comparison is necessary to validate the development of flow field vectors from the CVBEM and is of interest to many engineering flow problems, specifically groundwater modelling. Comparison of the CVBEM and FVM flow field trajectory vectors for the target problem of ideal flow in a 90-degree bend shows good agreement between the considered methodologies.

汽车空调流体管路的气动噪声分析与优化

以汽车空调风道为研究对象,在Fluent中采用RNG模型和LES模型对管路进行稳态和瞬态计算,对风道出口风量进行试验验证,并采用声类比法计算风道出风口的噪声。根据仿真分析结果,采用响应面法,以出风口1管路的转角半径、出风口2管路左、右管壁的移动距离为设计变量,以出风口2的风量占比为优化目标对空调管路的结构进行优化。最后对优化前、后的管路进行了流场和声场对比分析。结果表明,与原模型相比,优化后风道出风口2的风量比例由20.75%提升到了25.25%,出风口的噪声下降最大值为5.15dB。

氦冷固态包层氚增殖球床气体和粉末流动特性的数值研究

基于计算流体力学和离散元耦合分析,研究了氦冷固态增殖包层球床中吹扫氦气的速度分布和破碎的正硅酸锂粉末速度随时间的变化及粉末数量随氦气入口流速变化。模拟结果表明,在吹扫氦气流动方向上,用入口流速归一化的氦气速度分布与入口流速无关,在靠近球床边缘速度变化较大,在球床中部速度变化较小;用入口流速归一化的粉末平均速度与入口流速关系不大,会随吹扫时间逐渐趋于稳定;对小粒径粉末,吹扫气体流速越大,越容易被吹出球床,对大粒径粉末,因其本身体积过大,易在球床中形成堵塞。

基于神威加速计算架构的LBM多级并行计算

格子玻尔兹曼方法(lattice Boltzmann method,LBM)是一种基于分子运动理论计算流体力学(computational fluid dynamics,CFD)的方法,提高LBM的并行计算能力是高性能计算领域的一项重要的研究内容.本文基于SW26010Pro处理器,通过区域分解、数据重构、双缓冲、向量化等优化方法,实现了LBM的多级并行.基于以上优化方案,测试了5600万网格规模,实现结果显示,相比于MPI进行级并行,碰撞过程的平均加速倍数达到61.737、迁移过程的平均加速倍数达到17.3,同时对方腔流案例做了强扩展测试,网格规模为1200×1200×1200,以6.2万计算核心为基准,百万核心的并行效率超过60.5%.

Navier-Stokes方程间断Galerkin有限元方法研究

通过引入全局提升算子和局部提升算子,发展了求解Navier-Stokes方程的间断Galerkin(discontinuousGalerkin,DG)有限元方法的一般框架,并在此框架下给出了几种典型黏性离散格式的具体表达形式.对局部提升算子的求解给出了详细的计算步骤.同时还给出了一种简单有效的计算方法来对物面边界进行高阶近似.为了能够对NS方程进行精度测试,采用对原始系统添加源项的方法构造精确解.二维Euler和NS系统的精度测试表明该方法达到了DG方法的理论精度.二维圆柱无黏绕流的计算结果表明关于物面边界的高阶近似方法能够保持DG方法原有的精度.卡门涡街数值模拟则进一步验证了该方法的正确性并且显示出DG方法较高的计算精度和分辨率.

恶劣海况下船舶砰击颤振响应特性数值计算与试验研究

[目的]针对恶劣海况下船舶所受砰击颤振响应现象,探究船舶非线性波浪载荷与瞬态高幅值砰击载荷的耦合作用。[方法]采用计算流体动力学与有限元方法(CFD-FEM)相结合的双向流固耦合方法对S175集装箱船进行数值仿真计算,并与试验结果及切片理论计算结果进行对比验证;采用分段变截面弹性龙骨梁模型开展船舶的砰击颤振特性模型试验,基于CFD-FEM双向流固耦合方法开展船艏砰击载荷及高频非线性砰击颤振响应特性分析,并与模型试验结果进行对比验证。[结果]结果显示,波浪砰击载荷对船艏颤振响应的影响不可忽视,6级海况下由砰击颤振诱发的二阶高频成分分量占低频波浪弯矩的59.86%。[结论]采用基于CFD-FEM的双向流固耦合方法可准确计算船首砰击颤振响应;在高海况下船舶所受非线性波浪载荷及结构动态响应易受船首瞬态砰击载荷的影响,在船舶结构设计与安全评估中需考虑高频砰击颤振的情况。

基于雅可比矩阵精确计算的GMRES隐式方法在间断Galerkin有限元中的应用

为改善高阶间断Galerkin有限元方法(DG)时间推进效率,在三维非结构网格下针对该方法建立了并行广义最小残差(Generalized Minimal Residual,GMRES)隐式时间迭代方法,GMRES方法基于科学计算工具包PETSc中的Krylov子空间求解器实现。为进一步提高GMRES的计算效率,发展了方程组右端项残值雅可比精确计算方法,针对无黏通量Roe格式和黏性通量BR2(Bassi Rebay 2)黏性计算方法,分别解析给出其对守恒变量多项式自由度的雅可比矩阵。基于建立的方法首先采用NACA0012翼型研究了GMRES的重启次数及收敛参数对方法收敛性影响,然后采用无黏及黏性算例对比研究了基于雅可比矩阵不同计算方法的GMRES计算效率,同时对比研究了雅可比矩阵完全近似求解下GMRES和LU-SGS(Lower Upper-Symmetric Gauss-Seidel)的计算效率。结果表明,建立的基于右端项残值雅可比矩阵精确求解的GMRES方法能够大幅提高不同精度DG方法的CFL(CourantFriedrichs-Lewy)数,相比前面提到的其它方法具有更高的计算效率,其收敛速度实现量级以上的提高。

一种适用于非结构网格的间断Galerkin有限元LU-SGS隐式方法

具有TVD性质的显式Runge-Kutta间断Galerkin(RKDG)格式在CFD领域得到广泛应用,但是显式计算稳定性差、计算效率低。为改善时间推进效率,基于高阶间断Galerkin有限元方法,采用欧拉一阶后差(BDF1),发展了一套高效的隐式LU-SGS(lower upper-symmetric Gauss-Seidel)求解方法,方法基于MPI并行实现,适合于不同计算精度。针对非线性系统左端项矩阵,对比了简化前后LU-SGS的计算效率。建立的间断Galerkin有限元方法基于非结构网格,采用Taylor基函数,计算精度最高达到四阶精度。通过NACA0012翼型以及M6机翼算例对发展的LU-SGS方法进行了考察,与显式算法相比,隐式格式的迭代步数和CPU时间均较大程度减小,效率能够提高1个量级以上。最后将隐式算法用于复杂外形翼身组合体F4的流场计算,结果表明所发展的隐式方法具有较好的鲁棒性,能够用于复杂外形计算。

嫦娥五号发动机降落羽流扬尘特性研究

在月球探测器着陆过程中,发动机羽流与月面相互作用后溅起的月尘是月面环境危害的主要来源。本文以嫦娥五号任务测试数据作为仿真入口条件,采用计算流体动力学(CFD)两阶段法建立了嫦娥五号任务中使用的喷管1∶1模型和真空羽流扩散侵蚀模型,研究了喷管在不同降落高度下的侵蚀速率,并计算了发动机距离月面高度为0.5~2.0 m范围时月尘颗粒的运动轨迹、扬尘角和速度特性。结果表明,基于剪切应力得到的最大侵蚀速率为8.83 kg/m^(2)s,随着高度增加,侵蚀速率降低,与嫦娥五号降落相机相同高度下的分析结果一致。粒径为1、70ìm的月尘颗粒最大扬尘高度分别为0.72、0.36 m,最大速度分别为2520、1010 m/s。不同粒径月尘的扬尘角范围为1.44°~2.27°,计算的扬尘角与Apollo探月任务中的结果相近。