共查询到20条相似文献,搜索用时 140 毫秒
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基于Smagorinsky涡黏模型以及颗粒动理学理论,建立了气固两相流双大涡模拟模型。考虑大涡模拟中过滤尺度的影响,给出颗粒相亚格子压力和热传导系数计算模型。考虑颗粒聚团对两相作用的影响,给出了考虑颗粒聚团作用的气固两相多尺度曳力系数模型。数值模拟了提升管内气固两相流动特性,合理地预测出了提升管内气固两相环-核流动结构。模拟结果与Knowlton等实测结果相吻合。 相似文献
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We extend the mimetic finite difference (MFD) method to the numerical treatment of magnetostatic fields problems in mixed div–curl form for the divergence-free magnetic vector potential. To accomplish this task, we introduce three sets of degrees of freedom that are attached to the vertices, the edges, and the faces of the mesh, and two discrete operators mimicking the curl and the gradient operator of the differential setting. Then, we present the construction of two suitable quadrature rules for the numerical discretization of the domain integrals of the div–curl variational formulation of the magnetostatic equations. This construction is based on an algebraic consistency condition that generalizes the usual construction of the inner products of the MFD method. We also discuss the linear algebraic form of the resulting MFD scheme, its practical implementation, and discuss existence and uniqueness of the numerical solution by generalizing the concept of logically rectangular or cubic meshes by Hyman and Shashkov to the case of unstructured polyhedral meshes. The accuracy of the method is illustrated by solving numerically a set of academic problems and a realistic engineering problem. 相似文献
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使用混合网格计算非达西渗流 总被引:1,自引:0,他引:1
针对垂直裂缝井的特殊流动模式,从非达西定律出发,建立二维平面的非达西渗流方程.通过建立一组无量纲量,最终得到无量纲的渗流方程及其定解条件.假定外边界为圆形,用PEBI网格及混合网格对求解区域进行网格划分,用有限差分法对无量纲的方程进行离散,最终得到垂直裂缝井的井底压力数值解.根据此数值解并考虑井筒存储和表皮因子的影响,得到真实垂直裂缝井的井底压力.对计算结果的分析表明,使用混合网格求解非达西渗流井底压力相当准确,该方法也适用于水平井等更复杂井型及复杂边界的问题求解. 相似文献
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三维高超声速无粘定常绕流的数值模拟 总被引:13,自引:0,他引:13
本文采用一种简单有效的通量分裂结合一种二阶TVD格式的数值通量的方法,提出一种隐式的迎风有限体积格式,并利用这种格式,从气体动力学非定常Euler方程组出发,数值模拟了三维不对称物体的高超声速无粘定常绕流。数值结果表明此格式具有分辨率较高和收敛速度较快的优点。 相似文献
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An Immersed Boundary Method with Formal Second-Order Accuracy and Reduced Numerical Viscosity 总被引:1,自引:0,他引:1
A formally second-order accurate immersed boundary method is presented and tested in this paper. We apply this new scheme to simulate the flow past a circular cylinder and study the effect of numerical viscosity on the accuracy of the computation by comparing the numerical results with those of a first-order method. The numerical evidence shows that the new scheme has less numerical viscosity and is therefore a better choice for the simulation of high Reynolds number flows with immersed boundaries. 相似文献
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The maximum principle is one of the most important properties of solutions of partial differential equations. Its numerical analog, the discrete maximum principle (DMP), is one of the most difficult properties to achieve in numerical methods, especially when the computational mesh is distorted to adapt and conform to the physical domain or the problem coefficients are highly heterogeneous and anisotropic. Violation of the DMP may lead to numerical instabilities such as oscillations and to unphysical solutions such as heat flow from a cold material to a hot one. In this work, we investigate sufficient conditions to ensure the monotonicity of the mimetic finite difference (MFD) method on two- and three-dimensional meshes. These conditions result in a set of general inequalities for the elements of the mass matrix of every mesh element. Efficient solutions are devised for meshes consisting of simplexes, parallelograms and parallelepipeds, and orthogonal locally refined elements as those used in the AMR methodology. On simplicial meshes, it turns out that the MFD method coincides with the mixed-hybrid finite element methods based on the low-order Raviart–Thomas vector space. Thus, in this case we recover the well-established conventional angle conditions of such approximations. Instead, in the other cases a suitable design of the MFD method allows us to formulate a monotone discretization for which the existence of a DMP can be theoretically proved. Moreover, on meshes of parallelograms we establish a connection with a similar monotonicity condition proposed for the Multi-Point Flux Approximation (MPFA) methods. Numerical experiments confirm the effectiveness of the considered monotonicity conditions. 相似文献
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分形油藏非牛顿幂律流体低速非达西不稳定渗流的组合数学模型 总被引:9,自引:1,他引:8
结合分形理论与渗流理论,对分形油藏非牛顿幂律流体低速非达西不稳定渗流的试井分析问题的数学模型进行了推导.该分形油藏模型由内域为非牛顿幂律流体低速非达西渗流,外域为非牛顿幂律流体达西渗流的同心圆域组成.在考虑井筒储存、表皮效应影响下,建立了该油藏的不稳定渗流有效井径组合数学模型,在3种外边界条件下求出了两个区域内压力在Laplace空间的解析解,应用Stehfest数值反演方法求得井底的无因次压力,分析了井底压力动态特征和参数影响.非牛顿幂律流体的幂律指数、分形参数均对典型曲线产生较大的影响,呈现出与牛顿流体和均质油藏明显不同的特征.这对非均质油藏非牛顿流体的不稳定试井分析及研究其非线性渗流特征均十分重要. 相似文献
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We present an improved numerical scheme for numerical simulations of low Mach number turbulent reacting flows with detailed chemistry and transport. The method is based on a semi-implicit operator-splitting scheme with a stiff solver for integration of the chemical kinetic rates, developed by Knio et al. [O.M. Knio, H.N. Najm, P.S. Wyckoff, A semi-implicit numerical scheme for reacting flow II. Stiff, operator-split formulation, Journal of Computational Physics 154 (2) (1999) 428–467]. Using the material derivative form of continuity equation, we enhance the scheme to allow for large density ratio in the flow field. The scheme is developed for direct numerical simulation of turbulent reacting flow by employing high-order discretization for the spatial terms. The accuracy of the scheme in space and time is verified by examining the grid/time-step dependency on one-dimensional benchmark cases: a freely propagating premixed flame in an open environment and in an enclosure related to spark-ignition engines. The scheme is then examined in simulations of a two-dimensional laminar flame/vortex-pair interaction. Furthermore, we apply the scheme to direct numerical simulation of a homogeneous charge compression ignition (HCCI) process in an enclosure studied previously in the literature. Satisfactory agreement is found in terms of the overall ignition behavior, local reaction zone structures and statistical quantities. Finally, the scheme is used to study the development of intrinsic flame instabilities in a lean H2/air premixed flame, where it is shown that the spatial and temporary accuracies of numerical schemes can have great impact on the prediction of the sensitive nonlinear evolution process of flame instability. 相似文献
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针对圆柱坐标系下原始变量Navier Stokes方程,在有限控制容积法和压力修正的基础上,引入多重交错网格算法及非线性方程的FAS全近似格式,并对封闭圆柱空腔内的旋转流动进行数值模拟. 相似文献