A lattice Boltzmann flux solver(LBFS)is presented for simulation of fluid flows.Like the conventional computational fluid dynamics(CFD)solvers,the new solver also applies the finite volume method to discretize the gov...A lattice Boltzmann flux solver(LBFS)is presented for simulation of fluid flows.Like the conventional computational fluid dynamics(CFD)solvers,the new solver also applies the finite volume method to discretize the governing differential equations,but the numerical flux at the cell interface is not evaluated by the smooth function approximation or Riemann solvers.Instead,it is evaluated from local solution of lattice Boltzmann equation(LBE)at cell interface.Two versions of LBFS are presented in this paper.One is to locally apply one-dimensional compressible lattice Boltzmann(LB)model along the normal direction to the cell interface for simulation of compressible inviscid flows with shock waves.The other is to locally apply multi-dimensional LB model at cell interface for simulation of incompressible viscous and inviscid flows.The present solver removes the drawbacks of conventional lattice Boltzmann method(LBM)such as limitation to uniform mesh,tie-up of mesh spacing and time interval,limitation to viscous flows.Numerical examples show that the present solver can be well applied to simulate fluid flows with non-uniform mesh and curved boundary.展开更多
A reliable multiphase flow simulator is an important tool to improve wellbore integrity and production decision-making.To develop a multiphase flow model with high adaptability and high accuracy,we first build a multi...A reliable multiphase flow simulator is an important tool to improve wellbore integrity and production decision-making.To develop a multiphase flow model with high adaptability and high accuracy,we first build a multiphase flow database with 3561 groups of data and developed a drift closure relationship with stable continuity and high adaptability.Second,a high-order numerical scheme with strong fault capture ability is constructed by effectively combining MUSCL technology,van Albada slope limiter and AUSMV numerical scheme.Finally,the energy equation is coupled into the AUSMV numerical scheme of the drift flow model in the form of finite difference.A transient non-isothermal wellbore multiphase flow model with wide applicability is formed by integrating the three technologies,and the effects of various factors on the calculation accuracy are studied.The accuracy of the simulator is verified by comparing the measurement results with the blowout experiment of a full-scale experimental well.展开更多
研究舰艇附近水下爆炸问题对船体结构设计、爆炸冲击损害预测及人员安全保障至关重要。为此,提出改进扩散界面法中的六方程可压多相流模型以解决冲击波条件下热力学状态预测偏差,并为相关抗冲击机理研究与数值方法优化提供支撑。通过引...研究舰艇附近水下爆炸问题对船体结构设计、爆炸冲击损害预测及人员安全保障至关重要。为此,提出改进扩散界面法中的六方程可压多相流模型以解决冲击波条件下热力学状态预测偏差,并为相关抗冲击机理研究与数值方法优化提供支撑。通过引入混合能量校正方程及更精确的气体状态方程改进模型,在非结构网格系统构建数值算法程序,采用基于最小二乘重建和Barth-Jespersen限制器的二阶守恒定律的单调上游中心方案(Monotonic Upstream-centered Scheme for Conservation Laws,MUSCL)-Hancock格式、两相流带接触的Harten-Lax-van Leer(Harten-Lax-van Leer Contact,HLLC)黎曼求解器求解齐次双曲型方程,以Newton-Raphson迭代法求解瞬时压力松弛方程。研究结果表明:混合能量方程校正后,模型模拟流体冲击波速度和界面的结果与欧拉方程精确解高度吻合,解决界面附近数值振荡问题;相较于实验数据,改进型模型相对误差1.13%,准确度提升0.33%,且通过拟合冲击Hugoniot曲线获得更精确的刚性气体状态方程(Stiffened Gas Equation of State,SG-EOS)参数,同时可清晰呈现水下爆炸的冲击波传播、气泡胀缩及坍塌水射流现象,但在气泡界面清晰度、射流精细度上存在缺陷,主要受数值格式极端梯度下耗散特性限制。综上,改进型六方程可压多相流模型有效提升了舰艇附近水下爆炸模拟准确性,为深入研究舰艇抗冲击机理提供重要支撑,也为后续相关数值方法的优化奠定了坚实基础。展开更多
Finite volume schemes for the two-dimensional(2D) wave system are taken to demonstrate the role of the genuine dimensionality of Lax-Wendroff flow solvers for compressible fluid flows. When the finite volume schemes a...Finite volume schemes for the two-dimensional(2D) wave system are taken to demonstrate the role of the genuine dimensionality of Lax-Wendroff flow solvers for compressible fluid flows. When the finite volume schemes are applied, the transversal variation relative to the computational cell interfaces is neglected, and only the normal numerical flux is used, thanks to the Gauss-Green formula. In order to offset such defects, the Lax-Wendroff flow solvers or the generalized Riemann problem(GRP) solvers are adopted by substituting the time evolution of flows into the spatial variation. The numerical results show that even with the same convergence rate, the error by the GRP2D solver is almost one ninth of that by the multistage Runge-Kutta(RK) method.展开更多
A Harten-Lax-van Leer-contact （HLLC） approximate Riemann solver is built with elastic waves （HLLCE） for one-dimensional elastic-plastic flows with a hypo- elastic constitutive model and the von Mises＇ yielding cr...A Harten-Lax-van Leer-contact （HLLC） approximate Riemann solver is built with elastic waves （HLLCE） for one-dimensional elastic-plastic flows with a hypo- elastic constitutive model and the von Mises＇ yielding criterion. Based on the HLLCE, a third-order cell-centered Lagrangian scheme is built for one-dimensional elastic-plastic problems. A number of numerical experiments are carried out. The numerical results show that the proposed third-order scheme achieves the desired order of accuracy. The third-order scheme is used to the numerical solution of the problems with elastic shock waves and elastic rarefaction waves. The numerical results are compared with a reference solution and the results obtained by other authors. The comparison shows that the pre- sented high-order scheme is convergent, stable, and essentially non-oscillatory. Moreover, the HLLCE is more efficient than the two-rarefaction Riemann solver with elastic waves （TRRSE）展开更多
Environmental effects have an important influence on Offshore Wind Turbine (OWT) power generation efficiency and the structural stability of such turbines. In this study, we use an in-house Boundary Element (BEM)-panM...Environmental effects have an important influence on Offshore Wind Turbine (OWT) power generation efficiency and the structural stability of such turbines. In this study, we use an in-house Boundary Element (BEM)-panMARE code-to simulate the unsteady flow behavior of a full OWT with various combinations of aerodynamic and hydrodynamic loads in the time domain. This code is implemented to simulate potential flows for different applications and is based on a three-dimensional first-order panel method. Three different OWT configurations consisting of a generic 5 MW NREL rotor with three different types of foundations (Monopile, Tripod, and Jacket) are investigated. These three configurations are analyzed using the RANSE solver which is carried out using ANSYS CFX for validating the corresponding results. The simulations are performed under the same environmental atmospheric wind shear and rotor angular velocity, and the wave properties are wave height of 4 m and wave period of 7.16 s. In the present work, wave environmental effects were investigated firstly for the two solvers, and good agreement is achieved. Moreover, pressure distribution in each OWT case is presented, including detailed information about local flow fields. The time history of the forces at inflow direction and its moments around the mudline at each OWT part are presented in a dimensionless form with respect to the mean value of the last three loads and the moment amplitudes obtained from the BEM code, where the contribution of rotor force is lower in the tripod case and higher in the jacket case and the calculated hydrodynamic load that effect on jacket foundation type is lower than other two cases.展开更多
Flow transition from laminar to turbulent is prerequisite to decide whereabouts to apply surface flow control techniques. This appears missing in a number of works in which the control effects were merely investigated...Flow transition from laminar to turbulent is prerequisite to decide whereabouts to apply surface flow control techniques. This appears missing in a number of works in which the control effects were merely investigated without getting insight into alteration of transition position. The aim of this study is to capture the correct position of transition over NACA0012 aerofoil at different angles of attack. Firstly, an implicit, time marching, high resolution total variation diminishing （TVD） scheme was developed to solve the governing Navier-Stokes equations for compressible fluid flows around aerofoil sections to obtain velocity profiles around the aerofoil surfaces. Secondly, the linear instability solver based on the Orr-Sommerfeld equations and the eg methods were developed to calculate the onset of transition over the aerofoil surfaces. For the low subsonic Mach number of 0.16, the accuracy of the compressible solutions was assessed by some available experimental results of low speed incompressible flows. In all cases, transition positions were accurately predicted which shows applicability and superiority of the present work to be extended for higher Mach number compressible flows. Here, transition prediction methodology is described and the results of this analysis without active flow control or separation are presented.展开更多
A numerical method for two-phase flow with hydrodynamics behavior was considered. The nonconservative hyperbolic governing equations proposed by Saurel and Gallout were adopted. Dissipative effects were neglected but ...A numerical method for two-phase flow with hydrodynamics behavior was considered. The nonconservative hyperbolic governing equations proposed by Saurel and Gallout were adopted. Dissipative effects were neglected but they could be included in the model without major difficulties. Based on the opinion proposed by Abgrall that “a two phase system, uniform in velocity and pressure at t=0 will be uniform on the same variable during its temporal evolution", a simple accurate and fully Eulerian numerical method was presented for the simulation of multiphase compressible flows in hydrodynamic regime. The numerical method relies on Godunov-type scheme, with HLLC and Lax-Friedrichs type approximate Riemann solvers for the resolution of conservation equations, and nonconservative equation. Speed relaxation and pressure relaxation processes were introduced to account for the interaction between the phases. Test problem was presented in one space dimension which illustrated that our scheme is accurate, stable and oscillation free.展开更多
In this paper, a mathematical model that describes the flow of gas in a pipe is formulated. The model is simplified by making some assumptions. It is considered that the natural gas flowing in a long horizontal pipe, ...In this paper, a mathematical model that describes the flow of gas in a pipe is formulated. The model is simplified by making some assumptions. It is considered that the natural gas flowing in a long horizontal pipe, no heat source occurs inside the volume, transfer of heat due to heat conduction is dominated by heat exchange with the surrounding. The flow equations are coupled with equation of state. Different types of equations of state, ranging from the simple Ideal gas law to the more complex equation of state Benedict Webb Rubin Starling (BWRS), are considered. The flow equations are solved numerically using the Godunov scheme with Roe solver. Some numerical results are also presented.展开更多
基金Supported by the National Natural Science Foundation of China(11272153)
文摘A lattice Boltzmann flux solver(LBFS)is presented for simulation of fluid flows.Like the conventional computational fluid dynamics(CFD)solvers,the new solver also applies the finite volume method to discretize the governing differential equations,but the numerical flux at the cell interface is not evaluated by the smooth function approximation or Riemann solvers.Instead,it is evaluated from local solution of lattice Boltzmann equation(LBE)at cell interface.Two versions of LBFS are presented in this paper.One is to locally apply one-dimensional compressible lattice Boltzmann(LB)model along the normal direction to the cell interface for simulation of compressible inviscid flows with shock waves.The other is to locally apply multi-dimensional LB model at cell interface for simulation of incompressible viscous and inviscid flows.The present solver removes the drawbacks of conventional lattice Boltzmann method(LBM)such as limitation to uniform mesh,tie-up of mesh spacing and time interval,limitation to viscous flows.Numerical examples show that the present solver can be well applied to simulate fluid flows with non-uniform mesh and curved boundary.
基金The work was supported by the National Natural Science Foundation of China(No.51874045)National Natural Science Foundation-Youth Foundation(52104056)+2 种基金Department of Natural Resources of Guangdong Province(GDNRC[2021]56)Postdoctoral innovative talents support program in China(BX2021374)Scientific Research Program of Hubei Provincial Department of Education(T2021004).
文摘A reliable multiphase flow simulator is an important tool to improve wellbore integrity and production decision-making.To develop a multiphase flow model with high adaptability and high accuracy,we first build a multiphase flow database with 3561 groups of data and developed a drift closure relationship with stable continuity and high adaptability.Second,a high-order numerical scheme with strong fault capture ability is constructed by effectively combining MUSCL technology,van Albada slope limiter and AUSMV numerical scheme.Finally,the energy equation is coupled into the AUSMV numerical scheme of the drift flow model in the form of finite difference.A transient non-isothermal wellbore multiphase flow model with wide applicability is formed by integrating the three technologies,and the effects of various factors on the calculation accuracy are studied.The accuracy of the simulator is verified by comparing the measurement results with the blowout experiment of a full-scale experimental well.
文摘研究舰艇附近水下爆炸问题对船体结构设计、爆炸冲击损害预测及人员安全保障至关重要。为此,提出改进扩散界面法中的六方程可压多相流模型以解决冲击波条件下热力学状态预测偏差,并为相关抗冲击机理研究与数值方法优化提供支撑。通过引入混合能量校正方程及更精确的气体状态方程改进模型,在非结构网格系统构建数值算法程序,采用基于最小二乘重建和Barth-Jespersen限制器的二阶守恒定律的单调上游中心方案(Monotonic Upstream-centered Scheme for Conservation Laws,MUSCL)-Hancock格式、两相流带接触的Harten-Lax-van Leer(Harten-Lax-van Leer Contact,HLLC)黎曼求解器求解齐次双曲型方程,以Newton-Raphson迭代法求解瞬时压力松弛方程。研究结果表明:混合能量方程校正后,模型模拟流体冲击波速度和界面的结果与欧拉方程精确解高度吻合,解决界面附近数值振荡问题;相较于实验数据,改进型模型相对误差1.13%,准确度提升0.33%,且通过拟合冲击Hugoniot曲线获得更精确的刚性气体状态方程(Stiffened Gas Equation of State,SG-EOS)参数,同时可清晰呈现水下爆炸的冲击波传播、气泡胀缩及坍塌水射流现象,但在气泡界面清晰度、射流精细度上存在缺陷,主要受数值格式极端梯度下耗散特性限制。综上,改进型六方程可压多相流模型有效提升了舰艇附近水下爆炸模拟准确性,为深入研究舰艇抗冲击机理提供重要支撑,也为后续相关数值方法的优化奠定了坚实基础。
基金Project supported by the National Natural Science Foundation of China(Nos.11771054 and 91852207)
文摘Finite volume schemes for the two-dimensional(2D) wave system are taken to demonstrate the role of the genuine dimensionality of Lax-Wendroff flow solvers for compressible fluid flows. When the finite volume schemes are applied, the transversal variation relative to the computational cell interfaces is neglected, and only the normal numerical flux is used, thanks to the Gauss-Green formula. In order to offset such defects, the Lax-Wendroff flow solvers or the generalized Riemann problem(GRP) solvers are adopted by substituting the time evolution of flows into the spatial variation. The numerical results show that even with the same convergence rate, the error by the GRP2D solver is almost one ninth of that by the multistage Runge-Kutta(RK) method.
基金Project supported by the National Natural Science Foundation of China(Nos.11172050 and11672047)the Science and Technology Foundation of China Academy of Engineering Physics(No.2013A0202011)
文摘A Harten-Lax-van Leer-contact （HLLC） approximate Riemann solver is built with elastic waves （HLLCE） for one-dimensional elastic-plastic flows with a hypo- elastic constitutive model and the von Mises＇ yielding criterion. Based on the HLLCE, a third-order cell-centered Lagrangian scheme is built for one-dimensional elastic-plastic problems. A number of numerical experiments are carried out. The numerical results show that the proposed third-order scheme achieves the desired order of accuracy. The third-order scheme is used to the numerical solution of the problems with elastic shock waves and elastic rarefaction waves. The numerical results are compared with a reference solution and the results obtained by other authors. The comparison shows that the pre- sented high-order scheme is convergent, stable, and essentially non-oscillatory. Moreover, the HLLCE is more efficient than the two-rarefaction Riemann solver with elastic waves （TRRSE）
文摘Environmental effects have an important influence on Offshore Wind Turbine (OWT) power generation efficiency and the structural stability of such turbines. In this study, we use an in-house Boundary Element (BEM)-panMARE code-to simulate the unsteady flow behavior of a full OWT with various combinations of aerodynamic and hydrodynamic loads in the time domain. This code is implemented to simulate potential flows for different applications and is based on a three-dimensional first-order panel method. Three different OWT configurations consisting of a generic 5 MW NREL rotor with three different types of foundations (Monopile, Tripod, and Jacket) are investigated. These three configurations are analyzed using the RANSE solver which is carried out using ANSYS CFX for validating the corresponding results. The simulations are performed under the same environmental atmospheric wind shear and rotor angular velocity, and the wave properties are wave height of 4 m and wave period of 7.16 s. In the present work, wave environmental effects were investigated firstly for the two solvers, and good agreement is achieved. Moreover, pressure distribution in each OWT case is presented, including detailed information about local flow fields. The time history of the forces at inflow direction and its moments around the mudline at each OWT part are presented in a dimensionless form with respect to the mean value of the last three loads and the moment amplitudes obtained from the BEM code, where the contribution of rotor force is lower in the tripod case and higher in the jacket case and the calculated hydrodynamic load that effect on jacket foundation type is lower than other two cases.
文摘Flow transition from laminar to turbulent is prerequisite to decide whereabouts to apply surface flow control techniques. This appears missing in a number of works in which the control effects were merely investigated without getting insight into alteration of transition position. The aim of this study is to capture the correct position of transition over NACA0012 aerofoil at different angles of attack. Firstly, an implicit, time marching, high resolution total variation diminishing （TVD） scheme was developed to solve the governing Navier-Stokes equations for compressible fluid flows around aerofoil sections to obtain velocity profiles around the aerofoil surfaces. Secondly, the linear instability solver based on the Orr-Sommerfeld equations and the eg methods were developed to calculate the onset of transition over the aerofoil surfaces. For the low subsonic Mach number of 0.16, the accuracy of the compressible solutions was assessed by some available experimental results of low speed incompressible flows. In all cases, transition positions were accurately predicted which shows applicability and superiority of the present work to be extended for higher Mach number compressible flows. Here, transition prediction methodology is described and the results of this analysis without active flow control or separation are presented.
文摘A numerical method for two-phase flow with hydrodynamics behavior was considered. The nonconservative hyperbolic governing equations proposed by Saurel and Gallout were adopted. Dissipative effects were neglected but they could be included in the model without major difficulties. Based on the opinion proposed by Abgrall that “a two phase system, uniform in velocity and pressure at t=0 will be uniform on the same variable during its temporal evolution", a simple accurate and fully Eulerian numerical method was presented for the simulation of multiphase compressible flows in hydrodynamic regime. The numerical method relies on Godunov-type scheme, with HLLC and Lax-Friedrichs type approximate Riemann solvers for the resolution of conservation equations, and nonconservative equation. Speed relaxation and pressure relaxation processes were introduced to account for the interaction between the phases. Test problem was presented in one space dimension which illustrated that our scheme is accurate, stable and oscillation free.
文摘In this paper, a mathematical model that describes the flow of gas in a pipe is formulated. The model is simplified by making some assumptions. It is considered that the natural gas flowing in a long horizontal pipe, no heat source occurs inside the volume, transfer of heat due to heat conduction is dominated by heat exchange with the surrounding. The flow equations are coupled with equation of state. Different types of equations of state, ranging from the simple Ideal gas law to the more complex equation of state Benedict Webb Rubin Starling (BWRS), are considered. The flow equations are solved numerically using the Godunov scheme with Roe solver. Some numerical results are also presented.
